Publications
Ebrahimi S, Ostry DJ (2024) The human somatosensory cortex
contributes to the encoding of newly learned movements. PNAS
121: e2316294121.
Abstract
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PDF
Recent
studies have indicated somatosensory cortex involvement in
motor learning and retention. However, the nature of its
contribution is unknown. One possibility is that the
somatosensory cortex is transiently engaged during
movement. Alternatively, there may be durable
learning-related changes which would indicate sensory
participation in the encoding of learned movements. These
possibilities are dissociated by disrupting the
somatosensory cortex following learning, thus targeting
learning-related changes which may have occurred. If
changes to the somatosensory cortex contribute to
retention, which, in effect, means aspects of newly
learned movements are encoded there, disruption of this
area once learning is complete should lead to an
impairment. Participants were trained to make movements
while receiving rotated visual feedback. The primary motor
cortex (M1) and the primary somatosensory cortex (S1) were
targeted for continuous theta-burst stimulation, while
stimulation over the occipital cortex served as a control.
Retention was assessed using active movement reproduction,
or recognition testing, which involved passive movements
produced by a robot. Disruption of the somatosensory
cortex resulted in impaired motor memory in both tests.
Suppression of the motor cortex had no impact on retention
as indicated by comparable retention levels in control and
motor cortex conditions. The effects were learning
specific. When stimulation was applied to S1 following
training with unrotated feedback, movement direction, the
main dependent variable, was unaltered. Thus, the
somatosensory cortex is part of a circuit that contributes
to retention, consistent with the idea that aspects of
newly learned movements, possibly learning-updated sensory
states (new sensory targets) which serve to guide
movement, may be encoded there.
Darainy M, Manning TF (2023) Disruption of somatosensory
cortex impairs motor learning and retention. J Neurophysiol
130: 1521-1528.
Abstract
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PDF
This
study tests for a function of the somatosensory cortex,
that, in addition to its role in processing somatic
afferent information, somatosensory cortex contributes
both to motor learning and the stabilization of motor
memory. Continuous theta-burst magnetic stimulation (cTBS)
was applied, before force-field training to disrupt
activity in either the primary somatosensory cortex,
primary motor cortex, or a control zone over the occipital
lobe. Tests for retention and relearning were conducted
after a 24 h delay. Analysis of movement kinematic
measures and force-channel trials found that cTBS to
somatosensory cortex disrupted both learning and
subsequent retention, whereas cTBS to motor cortex had
little effect on learning but possibly impaired retention.
Basic movement variables are unaffected by cTBS suggesting
that the stimulation does not interfere with movement but
instead disrupts changes in the cortex that are necessary
for learning. In all experimental conditions, relearning
in an abruptly introduced force field, which followed
retention testing, showed extensive savings, which is
consistent with previous work suggesting that more
cognitive aspects of learning and retention are not
dependent on either of the cortical zones under test.
Taken together, the findings are consistent with the idea
that motor learning is dependent on learning-related
activity in the somatosensory cortex. NEW & NOTEWORTHY
This study uses noninvasive transcranial magnetic
stimulation to test the contribution of somatosensory and
motor cortex to human motor learning and retention.
Continuous theta-burst stimulation is applied before
learning; participants return 24 h later to assess
retention. Disruption of the somatosensory cortex is found
to impair both learning and retention, whereas disruption
of the motor cortex has no effect on learning. The
findings are consistent with the idea that motor learning
is dependent upon learning-related plasticity in
somatosensory cortex.
Franken M, Liu B, Ostry DJ (2022) Towards a somatosensory
theory of speech perception. J Neurophysiol 128: 1683-1695.
Abstract
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PDF
Towards a somatosensory theory of speech perception
Speech
perception is known to be a multimodal process, relying
not only on auditory input but also on the visual system
and possibly on the motor system as well. To date there
has been little work on the potential involvement of the
somatosensory sys- tem in speech perception. In the
present review, we identify the somatosensory system as
another contributor to speech per- ception. First, we
argue that evidence in favor of a motor contribution to
speech perception can just as easily be interpreted as
showing somatosensory involvement. Second, physiological
and neuroanatomical evidence for auditory-somatosensory
interac- tions across the auditory hierarchy indicates
the availability of a neural infrastructure that
supports somatosensory involvement in auditory
processing in general. Third, there is accumulating
evidence for somatosensory involvement in the context of
speech specifically. In particular, tactile stimulation
modifies speech perception, and speech auditory input
elicits activity in somatosen- sory cortical areas.
Moreover, speech sounds can be decoded from activity in
somatosensory cortex; lesions to this region affect
perception, and vowels can be identified based on
somatic input alone. We suggest that the somatosensory
involvement in speech perception derives from the
somatosensory-auditory pairing that occurs during speech
production and learning. By bringing together findings
from a set of studies that have not been previously
linked, the present article identifies the somato-
sensory system as a presently unrecognized contributor
to speech perception.
Ebrahimi S, Ostry DJ (2022) Persistence of adaptation
following visuomotor training. J Neurophysiol
128:1312-1323.
Abstract |
PDF
Retention tests
conducted after sensorimotor adaptation frequently
exhibit a rapid return to baseline performance once the
altered sensory feedback is removed. This so-called
washout of learning stands in contrast with other
demonstrations of retention, such as savings on
re-learning and anterograde interference effects of
initial learning on new learning. In the present study,
we tested the hypothesis that washout occurs when there
is a detectable discrepancy in retention tests between
visual information on the target position and
somatosensory information on the position of the limb.
Participants were tested following adaptation to
gradually rotated visual feedback (15 degree or 30
degree). Two different types of targets were used for
retention testing, a point target in which a perceptual
mismatch is possible, and an arc-target that eliminated
the mismatch. It was found that, except when point
targets were used, retention test movements were stable
throughout aftereffect trials, indicating little loss of
information. Substantial washout was only observed in
tests with a single point target, following adaptation
to a large amplitude 30 degree rotation. In control
studies designed to minimize the use of explicit
strategies during learning, we observed similar patterns
of decay when participants moved to point targets that
suggests that the effects observed here relate primarily
to implicit learning. The results suggest that washout
in aftereffect trials following visuomotor adaptation is
due to a detectable mismatch between vision and
somatosensation. When the mismatch is removed
experimentally, there is little evidence of loss of
information.NEW & NOTEWORTHY Aftereffects following
sensorimotor adaptation are important because they bear
on the understanding of the mechanisms that subserve
forgetting. We present evidence that information loss
previously reported during retention testing occurs only
when there is a detectable discrepancy between vision
and somatosensation and, if this mismatch is removed,
the persistence of adaptation is observed. This suggests
that washout during aftereffect trials is a consequence
of the experimental design rather than a property of the
memory system itself.
Kumar N, Sidarta A, Smith C, Ostry DJ (2022) Ventrolateral
prefrontal cortex contributes to human motor learning.
eNeuro
Abstract |
PDF
This study
assesses the involvement in human motor learning, of the
ventrolateral prefrontal cortex (BA 9/46v), a somatic
region in the middle frontal gyrus. The potential
involvement of this cortical area in motor learning is
suggested by studies in nonhuman primates which have
found anatomic connections between this area and
sensorimotor regions in frontal and parietal cortex, and
also with basal ganglia output zones. It is likewise
sug- gested by electrophysiological studies which have
shown that activity in this region is implicated in
somatic sensory memory and is also influenced by reward.
We directly tested the hypothesis that area 9/46v is in-
volved in reinforcement-based motor learning in humans.
Participants performed reaching movements to a hidden
target and received positive feedback when successful.
Before the learning task, we applied continu- ous theta
burst stimulation (cTBS) to disrupt activity in 9/46v in
the left or right hemisphere. A control group received
sham cTBS. The data showed that cTBS to left 9/46v
almost entirely eliminated motor learning, whereas
learning was not different from sham stimulation when
cTBS was applied to the same zone in the right
hemisphere. Additional analyses showed that the basic
reward-history-dependent pattern of movements was
preserved but more variable following left hemisphere
stimulation, which suggests an overall deficit in so-
matic memory for target location or target directed
movement rather than reward processing per se. The re-
sults indicate that area 9/46v is part of the human
motor learning circuit.
Sidarta A, Komar J, Ostry DJ (2022) Clustering analysis of
movement kinematics in reinforcement learning. J
Neurophysiol 127:341-353.
Abstract |
PDF
Reinforcement
learning has been used as an experimental model of motor
skill acquisition, where at times movements are suc-
cessful and thus reinforced. One fundamental problem is
to understand how humans select exploration over
exploitation during learning. The decision could be
influenced by factors such as task demands and reward
availability. In this study, we applied a clustering
algorithm to examine how a change in the accuracy
requirements of a task affected the choice of
exploration over ex- ploitation. Participants made
reaching movements to an unseen target using a planar
robot arm and received reward after each successful
movement. For one group of participants, the width of
the hidden target decreased after every other training
block. For a second group, it remained constant. The
clustering algorithm was applied to the kinematic data
to characterize motor learning on a trial-to-trial basis
as a sequence of movements, each belonging to one of the
identified clusters. By the end of learning, movement
trajectories across all participants converged primarily
to a single cluster with the greatest number of suc-
cessful trials. Within this analysis framework, we
defined exploration and exploitation as types of
behavior in which two succes- sive trajectories belong
to different or similar clusters, respectively. The
frequency of each mode of behavior was evaluated over
the course of learning. It was found that by reducing
the target width, participants used a greater variety of
different clusters and displayed more exploration than
exploitation. Excessive exploration relative to
exploitation was found to be detrimental to subsequent
motor learning. NEW & NOTEWORTHY The choice of
exploration versus exploitation is a fundamental problem
in learning new motor skills through reinforcement. In
this study, we employed a data-driven approach to
characterize movements on a trial-by-trial basis with an
unsupervised clustering algorithm. Using this technique,
we found that changes in task demands and, in
particular, in the required accuracy of movements,
influenced the ratio of exploration to exploitation.
This analysis framework provides an attractive tool to
investigate mechanisms of explorative and exploitative
behavior while studying motor learning.
Sedda G, Ostry DJ (2021) Self-operated stimuli improve
subsequent visual motion integration. J Vision 21:13,1-15.
Abstract |
PDF
Evidences of
perceptual changes that accompany motor activity have
been limited primarily to audition and somatosensation.
Here we asked whether motor learning results in changes
to visual motion perception. We designed a reaching task
in which participants were trained to make movements
along several directions, while the visual feedback was
provided by an intrinsically ambiguous moving stimulus
directly tied to hand motion. We find that training
improves coherent motion perception and that changes in
movement are correlated with perceptual changes. No
perceptual changes are observed in passive training even
when observers were provided with an explicit strategy
to facilitate single motion perception. A Bayesian model
suggests that movement training promotes the fine-tuning
of the internal representation of stimulus geometry.
These results emphasize the role of sensorimotor
interaction in determining the persistent properties in
space and time that define a percept.
Ohashi H, Ostry DJ (2021) Neural development of speech
sensorimotor learning. J Neurosci 41:4023-4035.
Abstract |
PDF
The development
of the human brain continues through to early adulthood.
It has been suggested that cortical plasticity during
this protracted period of development shapes circuits in
associative transmodal regions of the brain. Here we
considered how cortical plasticity during development
might contribute to the coordinated brain activity
required for speech motor learning. Specifically, we
examined patterns of brain functional connectivity whose
strength covaried with the capacity for speech
audio-motor adaptation in children ages 5-12 and in
young adults of both sexes. Children and adults showed
distinct patterns of the encoding of learning in the
brain. Adult performance was associated with
connectivity in transmodal regions that integrate
auditory and somatosensory information, whereas children
rely on basic somatosensory and motor circuits. A
progressive reliance on transmodal regions is consistent
with human cortical development and suggests that human
speech motor adaptation abilities are built on cortical
remodeling that is observable in late childhood and is
stabilized in adults.
Kumar N, van Vugt FT, Ostry DJ (2021) Recognition memory for
human motor learning. Curr Biol 31:1678-1686.
Abstract |
PDF
Motor skill
retention is typically measured by asking participants
to reproduce previously learned movements from memory.
The analog of this retention test (recall memory) in
human verbal memory is known to under-estimate how much
learning is actually retained. Here we asked whether
information about previously learned movements, which
can no longer be reproduced, is also retained. Following
visuomotor adaptation,we used tests of recall that
involved reproduction of previously learned movements
and tests of recognition in which participants were
asked whether a candidate limb displacement, produced by
a robot arm held by the subject, corresponded to a
movement direction that was experienced during active
training. The main finding was that 24 h after training,
estimates of recognition memory were about twice as
accurate as those of recall memory. Thus, there is
information about previously learned movements that is
not retrieved using recall testing but can be accessed
in tests of recognition. We conducted additional tests
to assess whether,24 h after learning, recall for
previously learned movements could be improved by
presenting passive movements as retrieval cues. These
tests were conducted immediately prior to recall testing
and involved the passive playback of a small number of
movements, which were spread across the workspace and
included both adapted and baseline movements, without
being marked as such. This technique restored recall
memory for movements to levels close to those of
recognition memory performance. Thus, somatic
information may enable retrieval of otherwise
inaccessible motor memories.
van Vugt FT, Near J, Hennessy T, Doyon J, Ostry DJ (2020)
Early stages of sensorimotor map acquisition: neurochemical
signature in primary motor cortex and its relation to
functional connectivity. J Neurophysiol 122: 1708-1720.
Abstract |
PDF
One of the
puzzles of learning to talk or play a musical instrument
is how we learn which movement produces a particular
sound: an audiomotor map. The initial stages of map
acquisition can be studied by having participants learn
arm movements to auditory targets. The key question is
what mechanism drives this early learning. Three
learning processes from previous literature were tested:
map learning may rely on active motor outflow (target),
on error correction, and on the correspondence between
sensory and motor distances (i.e., that similar
movements map to similar sounds). Alternatively, we
hypothesized that map learning can proceed without
these. Participants made movements that were mapped to
sounds in a number of different conditions that each
precluded one of the potential learning processes.We
tested whether map learning relies on assumptions about
topological continuity by exposing participants to a
permuted map that did not preserve distances in auditory
and motor space. Further groups were tested who
passively experienced the targets, kinematic
trajectories produced by a robot arm, and auditory
feedback as a yoked active participant (hence without
active motor outflow). Another group made movements
without receiving targets (thus without experiencing
errors). In each case we observed substantial
learning,therefore none of the three hypothesized
processes is required for learning. Instead early map
acquisition can occur with free exploration without
target error correction, is based on sensory-to-sensory
correspondences, and possible even for discontinuous
maps. The findings are consistent with the idea that
early sensorimotor map formation can involve
instance-specific learning. NEW & NOTEWORTHY: This
study tested learning of novel sensorimotor maps in a
variety of unusual circumstances, including learning a
mapping that was permuted in such as way that it
fragmented the sensorimotor workspace into discontinuous
parts, thus no preserving sensory and motor topology.
Participants could learn this mapping, and they could
learn without motor outflow or targets. These results
point to a robust learning mechanism building on
individual instances, inspired from machine learning
literature.
Ito T, Bai J, Ostry DJ (2020) Contribution of sensory memory
to speech motor learning. J Neurophysiol 124:1103-1109.
Abstract |
PDF
Speech learning requires precise
motor control, but it likewise requires transient
storage of information to enable the adjustment of
upcoming movements based on the success or failure of
previous attempts.The contribution of somatic sensory
memory for limb position has been documented in work on
arm movement; however, in speech,the sensory support for
speech production comes from both somatosensory and
auditory inputs, and accordingly sensory memory for
either or both of sounds and somatic inputs might
contribute to learning. In the present study, adaptation
to altered auditory feed-back was used as an
experimental model of speech motor learning.Participants
also underwent tests of both auditory and somatic
sensory memory. We found that although auditory memory
for speech sounds is better than somatic memory for
speech-like facial skin deformations, somatic sensory
memory predicts adaptation, where as auditory sensory
memory does not. Thus even though speech relies
substantially on auditory inputs and in the present
manipulation adaptation requires the minimization of
auditory error, it is somatic inputs that provide the
memory support for learning. NEW & NOTEWORTHY: In
speech production, almost everyone achieves an
exceptionally high level of proficiency. This is
remark-able because speech involves some of the smallest
and most care-fully timed movements of which we are
capable. The present paper demonstrates that sensory
memory contributes to speech motor learning. Moreover,
we report the surprising result that somatic sensory
memory predicts speech motor learning, whereas auditory
memory does not.
Patri JF, Ostry DJ, Diard J, Schwartz JL, Trudeau-Fisette P,
Savariaux C, Perrier P (2020) Speakers are able to
categorize vowels based on tongue somatosensation. Proc Natl
Acad Sci U S A. 117:6255-6263.
Abstract |
PDF
Auditory speech
perception enables listeners to access phonological
categories from speech sounds. During speech production
and speech motor learning, speakers' experience matched
auditory and somatosensory input. Accordingly, access to
phonetic units might also be provided by somatosensory
information.The present study assessed whether humans
can identify vowels using somatosensory feedback,
without auditory feedback.A tongue-positioning task was
used in which participants were required to achieve
different tongue postures within the /e,?, a/
articulatory range, in a procedure that was totally
non-speech like, involving distorted visual feedback of
tongue shape.Tongue postures were measured using
electromagnetic articulography. At the end of each
tongue-positioning trial, subjects were required to
whisper the corresponding vocal tract configuration with
masked auditory feedback and to identify the vowel
associated with the reached tongue posture. Masked
auditory feedback ensured that vowel categorization was
based on somatosensory feedback rather than auditory
feedback. A separate group of subjects was required to
auditorily classify the whispered sounds.In addition, we
modeled the link between vowel categories and tongue
postures in normal speech production with a Bayesian
classifier based on the tongue postures recorded from
the same speakers for several repetitions of the /e,?,
a/ vowels during a separate speech production task.
Overall, our results indicate that vowel categorization
is possible with somatosensory feed-back alone, with an
accuracy that is similar to the accuracy of the auditory
perception of whispered sounds, and in congruence with
normal speech articulation, as accounted for by the
Bayesian classifier.
Darainy M, Vahdat S, Ostry DJ (2019) Neural basis of
sensorimotor learning in speech motor adaptation. Cereb
Cortex 29:2876-2889.
Abstract |
PDF
Motor learning
is associated with plasticity in both motor and
somatosensory cortex. It is known from animal studies
that tetanic stimulation to each of these areas
individually induces long-term potentiation in its
counterpart. In this context it is possible that changes
in motor cortex contribute to somatosensory change and
that changes in somatosensory cortex are involved in
changes in motor areas of the brain. It is also possible
that learning-related plasticity occurs in these areas
independently. Tobetter understand the relative
contribution to human motor learning ofmotor cortical
and somatosensory plasticity, we assessed the time
course of changes in primary somatosensory and motor
cortex excitability during motor skill learning.
Learning was assessed using aforce production task in
which a target force profile varied from one trial to
the next. The excitability of primary somatosensory
cortex was measured using somatosensory evoked
potentials in response to median nerve stimulation. The
excitability of primary motor cortex was measured using
motor evoked potentials elicited by single-pulse
transcranial magnetic stimulation. These two measures
were inter-leaved with blocks of motor learning trials.
We found that the earliest changes in cortical
excitability during learning occurred in somatosensory
cortical responses, and these changes preceded changes
inmotor cortical excitability. Changes in somatosensory
evoked potentials were correlated with behavioral
measures of learning. Changes in motor evoked potentials
were not. These findings indicate that plasticity in
somatosensory cortex occurs as a part of the earliest
stages of motor learning, before changes in motor cortex
are observed.NEW & NOTEWORTHY: We tracked
somatosensory and motorcortical excitability during
motor skill acquisition. Changes in both motor cortical
and somatosensory excitability were observed during
learning; however, the earliest changes were in
somatosensory cortex,not motor cortex. Moreover, the
earliest changes in somatosensory cortical excitability
predict the extent of subsequent learning; those in
motor cortex do not. This is consistent with the idea
that plasticity insomatosensory cortex coincides with
the earliest stages of human motor learning.
Ohashi H, Valle-Mena R, Gribble P, Ostry DJ (2019) Movements
following force-field adaptation are aligned with altered
sense of limb position. Exp Brain Res 237:1303-1313.
Abstract |
PDF
Previous work
has shown that motor learning is associated with changes
to both movements and to the somatosensory perception of
limb position. In an earlier study that motivates the
current work, it appeared that following washout trials,
movements did not return to baseline but rather were
aligned with associated changes to sensed limb position.
Here, we provide a systematic test of this relationship,
examining the idea that adaptation-related changes to
sensed limb position and to the path of the limb are
linked, not only after washout trials but at all stages
of the adaptation process. We used a force-field
adaptation paradigm followed by washout trials in which
subjects performed movements without visual feedback of
the limb. Tests of sensed limb position were conducted
at each phase of adaptation, specifically before and
after baseline movements in a null field, after
force-field adaptation, and following washout trials in
a null field. As in previous work, sensed limb position
changed in association with force-field adaptation. At
each stage of adaptation, we observed a correlation
between the sensed limb position and associated path of
the limb. At a group level, there were differences
between the clockwise and counter-clockwise conditions.
However, whenever there were changes in sensed limb
position, movements following washout did not return to
baseline. This suggests that adaptation in sensory and
motor systems is not independent processes but rather
sensorimotor adaptation is linked to sensory change.
Sensory change and limb movement remain in alignment
throughout adaptation such that the path of the limb is
aligned with the altered sense of limb position.
van Vugt FT, Ostry DJ (2019) Early stages of sensorimotor
map acquisition: learning with free exploration, without
active movement or global structure. J Neurophysiol
122:1708-1720.
Abstract |
PDF
Early stages of
sensorimotor map acquisition: learning with free
exploration, without active movement or global
structure. J Neurophysiol 122: 1708-1720, 2019. First
published August 21, 2019; doi:10.1152/jn.00429.2019.
One of the puzzles of learning to talk or play a musical
instrument is how we learn which movement produces a
particular sound: an audiomotor map. The initial stages
of map acquisition can be studied by having participants
learn arm movements to auditory targets. The key
question is what mechanism drives this early learning.
Three learning processes from previous literature were
tested: map learning may rely on active motor outflow
(target), on error correction, and on the correspondence
between sensory and motor distances (i.e., that similar
movements map to similar sounds). Alternatively, we
hypothesized that map learning can proceed without
these. Participants made movements that were mapped to
sounds in a number of different conditions that each
precluded one of the potential learning processes. We
tested whether map learning relies on assumptions about
topological continuity by exposing participants to a
permuted map that did not preserve distances in auditory
and motor space. Further groups were tested who
passively experienced the targets, kinematic
trajectories produced by a robot arm, and auditory
feedback as a yoked active participant (hence without
active motor outflow). Another group made movements
without receiving targets (thus without experiencing
errors). In each case we observed substantial learning,
therefore none of the three hypothesized processes is
required for learning. Instead early map acquisition can
occur with free exploration without target error
correction, is based on sensory-to-sensory
correspondences, and possible even for discontinuous
maps. The findings are consistent with the idea that
early sensorimotor map formation can involve
instance-specific learning. NEW & NOTEWORTHY This
study tested learning of novel sensorimotor maps in a
variety of unusual circumstances, including learning a
mapping that was permuted in such as way that it
fragmented the sensorimotor workspace into discontinuous
parts, thus not preserving sensory and motor topology.
Participants could learn this mapping, and they could
learn without motor outflow or targets. These results
point to a robust learning mechanism building on
individual instances, inspired from machine learning
literature.
Kumar N, Manning TF, Ostry DJ (2019) Somatosensory cortex
participates in the consolidation of human motor memory.
PLoS Biol 17:e3000469.
Abstract |
PDF
Newly learned
motor skills are initially labile and then consolidated
to permit retention. The circuits that enable the
consolidation of motor memories remain uncertain. Most
work to date has focused on primary motor cortex, and
although there is ample evidence of learning-related
plasticity in motor cortex, direct evidence for its
involvement in memory consolidation is limited.
Learning-related plasticity is also observed in
somatosensory cortex, and accordingly, it may also be
involved in memory consolidation. Here, by using
transcranial magnetic stimulation (TMS) to block
consolidation, we report the first direct evidence that
plasticity in somatosensory cortex participates in the
consolidation of motor memory. Participants made
movements to targets while a robot applied forces to the
hand to alter somatosensory feedback. Immediately
following adaptation, continuous theta-burst
transcranial magnetic stimulation (cTBS) was delivered
to block retention; then, following a 24-hour delay,
which would normally permit consolidation, we assessed
whether there was an impairment. It was found that when
mechanical loads were introduced gradually to engage
implicit learning processes, suppression of
somatosensory cortex following training almost entirely
eliminated retention. In contrast, cTBS to motor cortex
following learning had little effect on retention at
all; retention following cTBS to motor cortex was not
different than following sham TMS stimulation. We
confirmed that cTBS to somatosensory cortex interfered
with normal sensory function and that it blocked motor
memory consolidation and not the ability to retrieve a
consolidated motor memory. In conclusion, the findings
are consistent with the hypothesis that in adaptation
learning, somatosensory cortex rather than motor cortex
is involved in the consolidation of motor memory.
Ohashi H, Gribble PL, Ostry DJ (2019) Somatosensory cortical
excitability changes precede those in motor cortex during
human motor learning. J Neurophysiol 122:1397-1405.
Abstract |
PDF
Motor learning
is associated with plasticity in both motor and
somatosensory cortex. It is known from animal studies
that tetanic stimulation to each of these areas
individually induces long-term potentiation in its
counterpart. In this context it is possible that changes
in motor cortex contribute to somatosensory change and
that changes in somatosensory cortex are involved in
changes in motor areas of the brain. It is also possible
that learning related plasticity occurs in these areas
independently. To better understand the relative
contribution to human motor learning of motor cortical
and somatosensory plasticity, we assessed the time
course of changes in primary somatosensory and motor
cortex excitability during motor skill learning.
Learning was assessed using a force production task in
which a target force profile varied from one trial to
the next. The excitability of primary somatosensory
cortex was measured using somatosensory evoked
potentials in response to median nerve stimulation. The
excitability of primary motor cortex was measured using
motor evoked potentials elicited by single-pulse
transcranial magnetic stimulation. These two measures
were interleaved with blocks of motor learning trials.
We found that the earliest changes in cortical
excitability during learning occurred in somatosensory
cortical responses and these changes preceded changes in
motor cortical excitability. Changes in somatosensory
evoked potentials were correlated with behavioral
measures of learning. Changes in motor evoked potentials
were not. These findings indicate that plasticity in
somatosensory cortex occurs as a part of the earliest
stages of motor learning, before changes in motor cortex
are observed.
Vahdat S, Darainy M, Thiel A, Ostry DJ (2018) A single
session of robot-controlled proprioceptive training
modulates functional connectivity of sensory motor networks
and improves reaching accuracy in chronic stroke
.Neurorehabil Neural Repair 33:70-81.
Abstract |
PDF
The relationship
between neural activation during movement training and
the plastic changes that survive beyond movement
execution is not well understood. Here we ask whether
the changes in resting-state functional connectivity
observed following motor learning overlap with the brain
networks that track movement error during training.
Human participants learned to trace an arched trajectory
using a computer mouse in an MRI scanner. Motor
performance was quantified on each trial as the maximum
distance from the prescribed arc. During learning, two
brain networks were observed, one showing increased
activations for larger movement error, comprising the
cerebellum, parietal, visual, somatosensory, and
cortical motor areas, and the other being more activated
for movements with lower error, comprising the ventral
putamen and the OFC. After learning, changes in brain
connectivity at rest were found predominantly in areas
that had shown increased activation for larger error
during task, specifically the cerebellum and its
connections with motor, visual, and somatosensory
cortex. The findings indicate that, although both errors
and accurate movements are important during the active
stage of motor learning, the changes in brain activity
observed at rest primarily reflect networks that process
errors. This suggests that error-related networks are
represented in the initial stages of motor memory
formation.
Sidarta A, van Vugt FT, Ostry DJ (2018) Somatosensory
working memory in human reinforcement-based motor learning.
J Neurophysiol 120:3275-3286.
Abstract |
PDF
Recent studies
using visuomotor adaptation and sequence learning tasks
have assessed the involvement of working memory in the
visuospatial domain. The capacity to maintain previously
performed movements in working memory is perhaps even
more important in reinforcement-based learning to repeat
accurate movements and avoid mistakes. Using this kind
of task in the present work, we tested the relationship
between somatosensory working memory and motor learning.
The first experiment involved separate memory and motor
learning tasks. In the memory task, the participant's
arm was displaced in different directions by a robotic
arm, and the participant was asked to judge whether a
subsequent test direction was one of the previously
presented directions. In the motor learning task,
participants made reaching movements to a hidden visual
target and were provided with positive feedback as
reinforcement when the movement ended in the target
zone. It was found that participants that had better
somatosensory working memory showed greater motor
learning. In a second experiment, we designed a new task
in which learning and working memory trials were
interleaved, allowing us to study participants memory
for movements they performed as part of learning. As in
the first experiment, we found that participants with
better somatosensory working memory also learned more.
Moreover, memory performance for successful movements
was better than for movements that failed to reach the
target. These results suggest that somatosensory working
memory is involved in reinforcement motor learning and
that this memory preferentially keeps track of
reinforced movements. NEW & NOTEWORTHY The present
work examined somatosensory working memory in
reinforcement-based motor learning. Working memory
performance was reliably correlated with the extent of
learning. With the use of a paradigm in which learning
and memory trials were interleaved, memory was assessed
for movements performed during learning. Movements that
received positive feedback were better remembered than
movements that did not. Thus working memory does not
track all movements equally but is biased to retain
movements that were rewarded.
Bernardi NF, Van Vugt FT, Valle-Mena R, Vahdat S, Ostry DJ
(2018) Error-related persistence of motor activity in
resting-state networks. J Cogn Neurosci 20:1-19.
Abstract |
PDF
Background.
Passive robot-generated arm movements in conjunction
with proprioceptive decision making and feedback
modulate functional connectivity (FC) in sensory motor
networks and improve sensorimotor adaptation in normal
individuals. This proof-of-principle study investigates
whether these effects can be observed in stroke
patients. Methods. A total of 10 chronic stroke patients
with a range of stable motor and sensory deficits
(Fugl-Meyer Arm score [FMA] 0-65, Nottingham Sensory
Assessment [NSA] 10-40) underwent resting-state
functional magnetic resonance imaging before and after a
single session of robot-controlled proprioceptive
training with feedback. Changes in FC were identified in
each patient using independent component analysis as
well as a seed region-based approach. FC changes were
related to impairment and changes in task performance
were assessed. Results. A single training session
improved average arm reaching accuracy in 6 and
proprioception in 8 patients. Two networks showing
training-associated FC change were identified. Network
C1 was present in all patients and network C2 only in
patients with FM scores >7. Relatively larger C1
volume in the ipsilesional hemisphere was associated
with less impairment (r = 0.83 for NSA, r = 0.73 for
FMA). This association was driven by specific regions in
the contralesional hemisphere and their functional
connections (supramarginal gyrus with FM scores r =
0.82, S1 with NSA scores r = 0.70, and cerebellum with
NSA score r = ?0.82). Conclusion. A single session of
robot-controlled proprioceptive training with feedback
improved movement accuracy and induced FC changes in
sensory motor networks of chronic stroke patients. FC
changes are related to functional impairment and
comprise bilateral sensory and motor network nodes.
Milner TE, Firouzimehr Z, Babadi S, Ostry DJ (2018)
Different adaptation rates to abrupt and gradual changes in
environmental dynamics. Exp Brain Res 236:2923-2933.
Abstract |
PDF
Adaptation to an
abrupt change in the dynamics of the interaction between
the arm and the physical environment has been reported
as occurring more rapidly but with less retention than
adaptation to a gradual change in interaction dynamics.
Faster adaptation to an abrupt change in interaction
dynamics appears inconsistent with kinematic error
sensitivity which has been shown to be greater for small
errors than large errors. However, the comparison of
adaptation rates was based on incomplete adaptation.
Furthermore, the metric which was used as a proxy of the
changing internal state, namely the linear regression
between the force disturbance and the compensatory force
(the adaptation index), does not distinguish between
internal state inaccuracy resulting from amplitude or
temporal errors. To resolve the apparent inconsistency,
we compared the evolution of the internal state during
complete adaptation to an abrupt and gradual change in
interaction dynamics. We found no difference in the rate
at which the adaptation index increased during
adaptation to a gradual compared to an abrupt change in
interaction dynamics. In addition, we separately
examined amplitude and temporal errors using different
metrics, and found that amplitude error was reduced more
rapidly under the gradual than the abrupt condition,
whereas temporal error (quantified by smoothness) was
reduced more rapidly under the abrupt condition. We did
not find any significant change in phase lag during
adaptation under either condition. Our results also
demonstrate that even after adaptation is complete,
online feedback correction still plays a significant
role in the control of reaching.
Van Vugt FT and Ostry DJ (2018) The structure and
acquisition of sensorimotor maps. J Cogn Neurosci 30:
290-306.
Abstract |
PDF
One of the
puzzles of learning to talk or play a musical instrument
is how we learn which movement produces a particular
sound: an audiomotor map. Existing research has used
mappings that are already well learned such as
controlling a cursor using a computer mouse. By
contrast, the acquisition of novel sensorimotor maps was
studied by having participants learn arm movements to
auditory targets. These sounds did not come from
different directions but, like speech, were only
distinguished by their frequencies. It is shown that
learning involves forming not one but two maps: a point
map connecting sensory targets with motor commands and
an error map linking sensory errors to motor
corrections. Learning a point map is possible even when
targets never repeat. Thus, although participants make
errors, there is no opportunity to correct them because
the target is different on every trial, and therefore
learning cannot be driven by error correction.
Furthermore, when the opportunity for error correction
is provided, it is seen that acquiring error correction
is itself a learning process that changes over time and
results in an error map. In principle, the error map
could be derived from the point map, but instead, these
two maps are independently acquired and jointly enable
sensorimotor control and learning. A computational model
shows that this dual encoding is optimal and simulations
based on this architecture predict that learning the two
maps results in performance improvements comparable with
those observed empirically.
Sidarta A, Vahdat S, Bernardi NF, Ostry DJ (2016) Somatic
and reinforcement-based plasticity in the initial stages of
human motor learning. J Neurosci 36:11682-11692.
Abstract |
PDF
As one learns to
dance or play tennis, the desired somatosensory state is
typically unknown. Trial and error is important as motor
behavior is shaped by successful and unsuccessful
movements. As an experimental model, we designed a task
in which human participants make reaching movements to a
hidden target and receive positive reinforcement when
successful. We identified somatic and
reinforcement-based sources of plasticity on the basis
of changes in functional connectivity using
resting-state fMRI before and after learning. The
neuroimaging data revealed reinforcement-related changes
in both motor and somatosensory brain areas in which a
strengthening of connectivity was related to the amount
of positive reinforcement during learning. Areas of
prefrontal cortex were similarly altered in relation to
reinforcement, with connectivity between sensorimotor
areas of putamen and the reward-related ventromedial
prefrontal cortex strengthened in relation to the amount
of successful feedback received. In other analyses, we
assessed connectivity related to changes in movement
direction between trials, a type of variability that
presumably reflects exploratory strategies during
learning. We found that connectivity in a network
linking motor and somatosensory cortices increased with
trial-to-trial changes in direction. Connectivity varied
as well with the change in movement direction following
incorrect movements. Here the changes were observed in a
somatic memory and decision making network involving
ventrolateral prefrontal cortex and second somatosensory
cortex. Our results point to the idea that the initial
stages of motor learning are not wholly motor but rather
involve plasticity in somatic and prefrontal networks
related both to reward and exploration.
Ito T, Coppola JH, Ostry DJ (2016) Speech motor learning
changes the neural response to both auditory and
somatosensory signals. Sci Rep 6:25926
Abstract |
PDF
In the present
paper, we present evidence for the idea that speech
motor learning is accompanied by changes to the neural
coding of both auditory and somatosensory stimuli.
Participants in our experiments undergo adaptation to
altered auditory feedback, an experimental model of
speech motor learning which like visuo-motor adaptation
in limb movement, requires that participants change
their speech movements and associated somatosensory
inputs to correct for systematic real-time changes to
auditory feedback. We measure the sensory effects of
adaptation by examining changes to auditory and
somatosensory event-related responses. We find that
adaptation results in progressive changes to speech
acoustical outputs that serve to correct for the
perturbation. We also observe changes in both auditory
and somatosensory event-related responses that are
correlated with the magnitude of adaptation. These
results indicate that sensory change occurs in
conjunction with the processes involved in speech motor
adaptation.
Ostry DJ, Gribble PL (2016) Sensory plasticity in human
motor learning. Trends Neurosci 39:114-123
Abstract
|
PDF
There is
accumulating evidence from behavioral,
neurophysiological, and neuroimaging studies that the
acquisition of motor skills involves both perceptual and
motor learning. Perceptual learning alters movements,
motor learning, and motor networks of the brain. Motor
learning changes perceptual function and the sensory
circuits of the brain. Here, we review studies of both
human limb movement and speech that indicate that
plasticity in sensory and motor systems is reciprocally
linked. Taken together, this points to an approach to
motor learning in which perceptual learning and sensory
plasticity have a fundamental role. Trends Sensorimotor
adaptation results in changes to sensory systems and
sensory networks in the brain. Perceptual learning
modifies sensory systems and directly alters the motor
networks of the brain. Perceptual changes associated
with sensorimotor adaptation are durable and occur in
parallel with motor learning.
Ito T, Ostry DJ, Gracco VL (2015) Somatosensory
event-related potentials from orofacial skin stretch
stimulation. J Vis Exp e53621-e53621
Abstract
|
PDF
Cortical
processing associated with orofacial somatosensory
function in speech has received limited experimental
attention due to the difficulty of providing precise and
controlled stimulation. This article introduces a
technique for recording somatosensory event-related
potentials (ERP) that uses a novel mechanical
stimulation method involving skin deformation using a
robotic device. Controlled deformation of the facial
skin is used to modulate kinesthetic inputs through
excitation of cutaneous mechanoreceptors. By combining
somatosensory stimulation with electroencephalographic
recording, somatosensory evoked responses can be
successfully measured at the level of the cortex.
Somatosensory stimulation can be combined with the
stimulation of other sensory modalities to assess
multisensory interactions. For speech, orofacial
stimulation is combined with speech sound stimulation to
assess the contribution of multi-sensory processing
including the effects of timing differences. The ability
to precisely control orofacial somatosensory stimulation
during speech perception and speech production with ERP
recording is an important tool that provides new insight
into the neural organization and neural representations
for speech.
Bernardi NF, Darainy M, Ostry DJ (2015) Somatosensory
contribution to the early stages of motor skill learning. J
Neurosci 35: 14316 -14326
Abstract |
PDF
The early stages
of motor skill acquisition are often marked by
uncertainty about the sensory and motor goals of the
task, as is the case in learning to speak or learning
the feel of a good tennis serve. Here we present an
experimental model of this early learning process, in
which targets are acquired by exploration and
reinforcement rather than sensory error. We use this
model to investigate the relative contribution of motor
and sensory factors to human motor learning.
Participants make active reaching movements or matched
passive movements to an unseen target using a robot arm.
We find that learning through passive movements paired
ith reinforcement is comparable with learning associated
with active movement, both in terms of magnitude and
durability, with improvements due to training still
observable at a 1 week retest. Motor learning is also
accompanied by changes in somatosensory perceptual
acuity. No stable changes in motor performance are
observed for participants that train, actively or
passively, in the absence of reinforcement, or for
participants who are given explicit information about
target position in the absence of somatosensory
experience. These findings indicate that the
somatosensory system dominates learning in the early
stages of motor skill acquisition.
Lametti DR, Rochet-Capellan A, Neufeld E, Shiller DM, Ostry
DJ (2014) Plasticity in the human speech motor system drives
changes in speech perception. J Neurosci 34:10339-10346.
Abstract |
PDF
Recent studies
of human speech motor learning suggest that learning is
accompanied by changes in auditory perception. But what
drives the perceptual change? Is it a consequence of
changes in the motor system? Or is it a result of
sensory inflow during learning? Here, subjects
participated in a speech motor-learning task involving
adaptation to altered auditory feedback and they were
subsequently tested for perceptual change. In two
separate experiments, involving two different auditory
perceptual continua, we show that changes in the speech
motor system that accompany learning drive changes in
auditory speech perception. Specifically, we obtained
changes in speech perception when adaptation to altered
auditory feedback led to speech production that fell
into the phonetic range of the speech perceptual tests.
However, a similar change in perception was not observed
when the auditory feedback that subjects' received
during learning fell into the phonetic range of the
perceptual tests. This indicates that the central motor
outflow associated with vocal sensorimotor adaptation
drives changes to the perceptual classification of
speech sounds.
Lametti DR, Krol SA, Shiller DM, Ostry DJ (2014) Brief
periods of auditory perceptual training can determine the
sensory targets of speech motor learning. Psychol Sci.
25:1325-1336.
Abstract |
PDF
The perception
of speech is notably malleable in adults, yet
alterations in perception seem to have little impact on
speech production. However, we hypothesized that speech
perceptual training might immediately influence speech
motor learning. To test this, we paired a speech
perceptual-training task with a speech motor-learning
task. Subjects performed a series of perceptual tests
designed to measure and then manipulate the perceptual
distinction between the words head and had. Subjects
then produced head with the sound of the vowel altered
in real time so that they heard themselves through
headphones producing a word that sounded more like had.
In support of our hypothesis, the amount of motor
learning in response to the voice alterations depended
on the perceptual boundary acquired through perceptual
training. The studies show that plasticity in adults'
speech perception can have immediate consequences for
speech production in the context of speech learning.
Ito T, Johns AR, Ostry DJ (2014) Left lateralized
enhancement of orofacial somatosensory processing due to
speech sounds. J Speech Lang Hear Res. 56:1875-81.
Abstract |
PDF
PURPOSE:
Somatosensory information associated with speech
articulatory movements affects the perception of speech
sounds and vice versa, suggesting an intimate linkage
between speech production and perception systems.
However, it is unclear which cortical processes are
involved in the interaction between speech sounds and
orofacial somatosensory inputs. The authors examined
whether speech sounds modify orofacial somatosensory
cortical potentials that were elicited using facial skin
perturbations.
METHOD:
Somatosensory event-related potentials in EEG were
recorded in 3 background sound conditions (pink noise,
speech sounds, and nonspeech sounds) and also in a
silent condition. Facial skin deformations that are
similar in timing and duration to those experienced in
speech production were used for somatosensory
stimulation.
RESULTS:
The authors found that speech sounds reliably enhanced
the first negative peak of the somatosensory
event-related potential when compared with the other 3
sound conditions. The enhancement was evident at
electrode locations above the left motor and premotor
area of the orofacial system. The result indicates that
speech sounds interact with somatosensory cortical
processes that are produced by speech-production-like
patterns of facial skin stretch.
CONCLUSION:
Neural circuits in the left hemisphere, presumably in
left motor and premotor cortex, may play a prominent
role in the interaction between auditory inputs and
speech-relevant somatosensory processing.
Vahdat S, Darainy M, Ostry DJ (2014) Structure of plasticity
in human sensory and motor networks due to perceptual
learning. J Neurosci 34:2451-63.
Abstract |
PDF
As we begin to
acquire a new motor skill, we face the dual challenge of
determining and refining the somatosensory goals of our
movements and establishing the best motor commands to
achieve our ends. The two typically proceed in parallel,
and accordingly it is unclear how much of skill
acquisition is a reflection of changes in sensory
systems and how much reflects changes in the brain's
motor areas. Here we have intentionally separated
perceptual and motor learning in time so that we can
assess functional changes to human sensory and motor
networks as a result of perceptual learning. Our
subjects underwent fMRI scans of the resting brain
before and after a somatosensory discrimination task. We
identified changes in functional connectivity that were
due to the effects of perceptual learning on movement.
For this purpose, we used a neural model of the
transmission of sensory signals from perceptual decision
making through to motor action. We used this model in
combination with a partial correlation technique to
parcel out those changes in connectivity observed in
motor systems that could be attributed to activity in
sensory brain regions. We found that, after removing
effects that are linearly correlated with somatosensory
activity, perceptual learning results in changes to
frontal motor areas that are related to the effects of
this training on motor behavior and learning. This
suggests that perceptual learning produces changes to
frontal motor areas of the brain and may thus contribute
directly to motor learning.
Darainy M, Vahdat S, Ostry DJ (2013) Perceptual learning in
sensorimotor adaptation. J Neurophysiol 110: 2152-2162.
Abstract | PDF
Motor learning
often involves situations in which the somatosensory
targets of movement are initially, poorly defined, as
for example, in learning to speak or learning the feel
of a proper tennis serve. Under these conditions, motor
skill acquisition presumably requires perceptual as well
as motor learning. That is, it engages both the
progressive shaping of sensory targets and associated
changes in motor performance. In the present paper, we
test the idea that perceptual learning alters
somatosensory function and in so doing produces changes
to motor performance and sensorimotor adaptation.
Subjects in these experiments undergo perceptual
training in which a robotic device passively moves the
arm on one of a set of fan shaped trajectories. Subjects
are required to indicate whether the robot moved the
limb to the right or the left and feedback is provided.
Over the course of training both the perceptual boundary
and acuity are altered. The perceptual learning is
observed to improve both the rate and extent of learning
in a subsequent sensorimotor adaptation task and the
benefits persist for at least 24 hours. The improvement
in the present studies is obtained regardless of whether
the perceptual boundary shift serves to systematically
increase or decrease error on subsequent movements. The
beneficial effects of perceptual training are found to
be substantially dependent upon reinforced
decision-making in the sensory domain. Passive-movement
training on its own is less able to alter subsequent
learning in the motor system. Overall, this study
suggests perceptual learning plays an integral role in
motor learning.
Bernardi NF, Darainy M, Bricolo E, Ostry DJ (2013) Observing
motor learning produces somatosensory change. J Neurophysiol
110: 1804-1810.
Abstract |
PDF
Observing the
actions of others has been shown to affect motor
learning, but does it have effects on sensory systems as
well? It has been recently shown that motor learning
that involves actual physical practice is also
associated with plasticity in the somatosensory system.
Here, we assessed the idea that observational learning
likewise changes somatosensory function. We evaluated
changes in somatosensory function after human subjects
watched videos depicting motor learning. Subjects first
observed video recordings of reaching movements either
in a clockwise or counterclockwise force field. They
were then trained in an actual force-field task that
involved a counterclockwise load. Measures of
somatosensory function were obtained before and after
visual observation and also following force-field
learning. Consistent with previous reports, video
observation promoted motor learning. We also found that
somatosensory function was altered following
observational learning, both in direction and in
magnitude, in a manner similar to that which occurs when
motor learning is achieved through actual physical
practice. Observation of the same sequence of movements
in a randomized order did not result in somatosensory
perceptual change. Observational learning and real
physical practice appear to tap into the same capacity
for sensory change in that subjects that showed a
greater change following observational learning showed a
reliably smaller change following physical motor
learning. We conclude that effects of observing motor
learning extend beyond the boundaries of traditional
motor circuits, to include somatosensory
representations.
Ito S, Darainy M, Sasaki M, Ostry DJ (2013) Computational
model of motor learning and perceptual change. Biol Cybern
107:653-667.
Abstract |
PDF
Motor learning
in the context of arm reaching movements has been
frequently investigated using the paradigm of
force-field learning. It has been recently shown that
changes to somatosensory perception are likewise
associated with motor learning. Changes in perceptual
function may be the reason that when the perturbation is
removed following motor learning, the hand trajectory
does not return to a straight line path even after
several dozen trials. To explain the computational
mechanisms that produce these characteristics, we
propose a motor control and learning scheme using a
simplified two-link system in the horizontal plane:We
represent learning as the adjustment of desired
joint-angular trajectories so as to achieve the
reference trajectory of the hand. The convergence of the
actual hand movement to the reference trajectory is
proved by using a Lyapunov-like lemma, and the result is
confirmed using computer simulations. The model assumes
that changes in the desired hand trajectory influence
the perception of hand position and this in turn affects
movement control. Our computer simulations support the
idea that perceptual change may come as a result of
adjustments to movement planning with motor learning.
Nasir SM, Darainy M, Ostry DJ (2013) Sensorimotor adaptation
changes the neural coding of somatosensory stimuli. J.
Neurophysiol. 109:2077-85.
Abstract |
PDF
Motor learning
is reflected in changes to the brain's functional
organization as a result of experience. We show here
that these changes are not limited to motor areas of the
brain and indeed that motor learning also changes
sensory systems. We test for plasticity in sensory
systems using somatosensory evoked potentials (SEPs). A
robotic device is used to elicit somatosensory inputs by
displacing the arm in the direction of applied force
during learning. We observe that following learning
there are short latency changes to the response in
somatosensory areas of the brain that are reliably
correlated with the magnitude of motor learning:
subjects who learn more show greater changes in SEP
magnitude. The effects we observe are tied to motor
learning. When the limb is displaced passively, such
that subjects experience similar movements but without
experiencing learning, no changes in the evoked response
are observed. Sensorimotor adaptation thus alters the
neural coding of somatosensory stimuli.
Mattar AAG, Darainy M, Ostry DJ (2013) Motor learning and
its sensory effects: The time course of perceptual change,
and its presence with gradual introduction of load. J.
Neurophysiol. 109:782-91.
Abstract |
PDF
A complex
interplay has been demonstrated between motor and
sensory systems. We showed recently that motor learning
leads to changes in the sensed position of the limb
(Ostry DJ, Darainy M, Mattar AA, Wong J, Gribble PL. J
Neurosci 30: 5384-5393, 2010). Here, we document further
the links between motor learning and changes in
somatosensory perception. To study motor learning, we
used a force field paradigm in which subjects learn to
compensate for forces applied to the hand by a robotic
device. We used a task in which subjects judge lateral
displacements of the hand to study somatosensory
perception. In a first experiment, we divided the motor
learning task into incremental phases and tracked
sensory perception throughout. We found that changes in
perception occurred at a slower rate than changes in
motor performance. A second experiment tested whether
awareness of the motor learning process is necessary for
perceptual change. In this experiment, subjects were
exposed to a force field that grew gradually in
strength. We found that the shift in sensory perception
occurred even when awareness of motor learning was
reduced. These experiments argue for a link between
motor learning and changes in somatosensory perception,
and they are consistent with the idea that motor
learning drives sensory change.
Lametti DR, Nasir S, Ostry DJ (2012) Sensory preference in
speech production revealed by simultaneous alteration of
auditory and somatosensory feedback. J Neurosci
32:9351-9359.
Abstract |
PDF
The idea that
humans learn and maintain accurate speech by carefully
monitoring auditory feedback is widely held. But this
view neglects the fact that auditory feedback is highly
correlated with somatosensory feedback during speech
production. Somatosensory feedback from speech movements
could be a primary means by which cortical speech areas
monitor the accuracy of produced speech. We tested this
idea by placing the somatosensory and auditory systems
in competition during speech motor learning. To do this,
we combined two speech-learning paradigms to
simultaneously alter somatosensory and auditory feedback
in real time as subjects spoke. Somatosensory feedback
was manipulated by using a robotic device that altered
the motion path of the jaw. Auditory feedback was
manipulated by changing the frequency of the first
formant of the vowel sound and playing back the modified
utterance to the subject through headphones. The amount
of compensation for each perturbation was used as a
measure of sensory reliance. All subjects were observed
to correct for at least one of the perturbations, but
auditory feedback was not dominant. Indeed, some
subjects showed a stable preference for either
somatosensory or auditory feedback during speech.
Rochet-Capellan A, Richer L, Ostry DJ (2012) Non-homogeneous
transfer reveals specificity in speech motor learning, J
Neurophysiol 107(6):1711-1717.
Abstract |
PDF
Does motor
learning generalize to new situations that are not
experienced during training, or is motor learning
essentially specific to the training situation? In the
present experiments, we use speech production as a model
to investigate generalization in motor learning. We
tested for generalization from training to transfer
utterances by varying the acoustical similarity between
these two sets of utterances. During the training phase
of the experiment, subjects received auditory feedback
that was altered in real time as they repeated a single
consonant vowel-consonant utterance. Different groups of
subjects were trained with different
consonant-vowel-consonant utterances, which differed
from a subsequent transfer utterance in terms of the
initial consonant or vowel. During the adaptation phase
of the experiment, we observed that subjects in all
groups progressively changed their speech output to
compensate for the perturbation (altered auditory
feedback). After learning, we tested for generalization
by having all subjects produce the same single transfer
utterance while receiving unaltered auditory feedback.
We observed limited transfer of learning, which depended
on the acoustical similarity between the training and
the transfer utterances. The gradients of generalization
observed here are comparable to those observed in limb
movement. The present findings are consistent with the
conclusion that speech learning remains specific to
individual instances of learning.
Mattar AAG, Nasir SM, Darainy M, Ostry DJ (2011) Sensory
change following motor learning. in Green AM, Chapman CE,
Kalaska JF and Lepore F (Eds), Progress in Brain Research,
Volume 191 (pp 29-42).
Abstract |
PDF
Here we describe
two studies linking perceptual change with motor
learning. In the first, we document persistent changes
in somatosensory perception that occur following force
field learning. Subjects learned to control a robotic
device that applied forces to the hand during arm
movements. This led to a change in the sensed position
of the limb that lasted at least 24 h. Control
experiments revealed that the sensory change depended on
motor learning. In the second study, we describe changes
in the perception of speech sounds that occur following
speech motor learning. Subjects adapted control of
speech movements to compensate for loads applied to the
jaw by a robot. Perception of speech sounds was measured
before and after motor learning. Adapted subjects showed
a consistent shift in perception. In contrast, no
consistent shift was seen in control subjects and
subjects that did not adapt to the load. These studies
suggest that motor learning changes both sensory and
motor function.
Vahdat S, Darainy M, Milner TE, Ostry DJ (2011) Functionally
specific changes in resting-state sensorimotor networks
after motor learning. J Neurosci. 31:16907-16915.
Abstract |
PDF
Motor learning
changes the activity of cortical motor and subcortical
areas of the brain, but does learning affect sensory
systems as well? We examined inhumansthe effects of
motor learning using fMRI measures of functional
connectivity under resting conditions and found
persistent changes in networks involving both motor and
somatosensory areas of the brain. We developed a
technique that allows us to distinguish changes in
functional connectivity that can be attributed to motor
learning from those that are related to perceptual
changes that occur in conjunction with learning. Using
this technique, we identified a new network in motor
learning involving second somatosensory cortex, ventral
premotor cortex, and supplementary motor cortex whose
activation is specifically related to perceptual changes
that occur in conjunction with motor learning. We also
found changes in a network comprising cerebellar cortex,
primary motor cortex, and dorsal premotor cortex that
were linked to the motor aspects of learning. In each
network, we observed highly reliable linear
relationships between neuroplastic changes and
behavioral measures of either motor learning or
perceptual function. Motor learning thus results in
functionally specific changes to distinct resting-state
networks in the brain.
Rochet-Capellan A, Ostry DJ (2011) Simultaneous acquisition
of multiple auditory-motor transformations in speech. J
Neurosci. 31:2648-2655.
Abstract |
PDF
The brain easily
generates the movement that is needed in a given
situation. Yet surprisingly, the results of experimental
studies suggest that it is difficult to acquire more
than one skill at a time. To do so, it has generally
been necessary to link the required movement to
arbitrary cues. In the present study, we show that
speech motor learning provides an informative model for
the acquisition of multiple sensorimotor skills. During
training, subjects were required to repeat aloud
individual words in random order while auditory feedback
was altered in real-time in different ways for the
different words. We found that subjects can quite
readily and simultaneously modify their speech movements
to correct for these different auditory transformations.
This multiple learning occurs effortlessly without
explicit cues and without any apparent awareness of the
perturbation. The ability to simultaneously learn
several different auditory-motor transformations is
consistent with the idea that, in speech motor learning,
the brain acquires instance-specific memories. The
results support the hypothesis that speech motor
learning is fundamentally local.
Ito T, Ostry DJ (2010) Somatosensory contribution to motor
learning due to facial skin deformation. J Neurophysiol
104:1230-1230.
Abstract |
PDF
Motor learning
is dependent on kinesthetic information that is obtained
both from cutaneous afferents and from muscle receptors.
In human arm movement, information from these two kinds
of afferents is largely correlated. The facial skin
offers a unique situation in which there are plentiful
cutaneous afferents and essentially no muscle receptors
and, accordingly, experimental manipulations involving
the facial skin may be used to assess the possible role
of cutaneous afferents in motor learning. We focus here
on the information for motor learning provided by the
deformation of the facial skin and the motion of the
lips in the context of speech. We used a robotic device
to slightly stretch the facial skin lateral to the side
of the mouth in the period immediately preceding
movement. We found that facial skin stretch increased
lip protrusion in a progressive manner over the course
of a series of training trials. The learning was
manifest in a changed pattern of lip movement, when
measured after learning in the absence of load. The
newly acquired motor plan generalized partially to
another speech task that involved a lip movement of
different amplitude. Control tests indicated that the
primary source of the observed adaptation was sensory
input from cutaneous afferents. The progressive increase
in lip protrusion over the course of training fits with
the basic idea that change in sensory input is
attributed to motor performance error. Sensory input,
which in the present study precedes the target movement,
is credited to the target-related motion, even though
the skin stretch is released prior to movement
initiation. This supports the idea that the nervous
system generates motor commands on the assumption that
sensory input and kinematic error are in register.
Lametti DR, Ostry DJ (2010) Postural constraint on movement
variability. J Neurophysiol 104:1061-1067.
Abstract |
PDF
Movements are
inherently variable. When we move to a particular point
in space, a cloud of final limb positions is observed
around the target. Previously we noted that
patterns of variability at the end of movement to a
circular target were not circular, but instead reflected
patterns of limb stiffness in directions where limb
stiffness was high, variability in end position was low,
and vice versa. Here we examine the determinants of
variability at movement end in more detail. To do this,
we have subjects move the handle of a robotic device
from different starting positions into a circular
target. We use position servocontrolled displacements of
the robot's handle to measure limb stiffness at the end
of movement and we also record patterns of end position
variability. To examine the effect of change in posture
on movement variability, we use a visual motor
transformation in which we change the limb configuration
and also the actual movement target, while holding
constant the visual display. We find that, regardless of
movement direction, patterns of variability at the end
of movement vary systematically with limb configuration
and are also related to patterns of limb stiffness,
which are likewise configuration dependent. The result
suggests that postural configuration determines the base
level of movement variability, on top of which control
mechanisms can act to further alter variability.
Mattar AAG, Ostry DJ (2010) Generalization of dynamics
learning across changes in movement amplitude. J
Neurophysiol 104:426-438.
Abstract |
PDF
Studies on
generalization show the nature of how learning is
encoded in the brain. Previous studies have shown rather
limited generalization of dynamics learning across
changes in movement direction, a finding that is
consistent with the idea that learning is primarily
local. In contrast, studies show a broader pattern of
generalization across changes in movement amplitude,
suggesting a more general form of learning. To
understand this difference, we performed an experiment
in which subjects held a robotic manipulandum and made
movements to targets along the body midline. Subjects
were trained in a velocitydependent force field while
moving to a 15 cm target. After training, subjects were
tested for generalization using movements to a 30 cm
target. We used force channels in conjunction with
movements to the 30 cm target to assess the extent of
generalization. Force channels restricted lateral
movements and allowed us to measure force production
during generalization. We compared actual lateral forces
to the forces expected if dynamics learning generalized
fully. We found that, during the test for
generalization, subjects produced reliably less force
than expected. Force production was appropriate for the
portion of the transfer movement in which velocities
corresponded to those experienced with the 15 cm target.
Subjects failed to produce the expected forces when
velocities exceeded those experienced in the training
task. This suggests that dynamics learning generalizes
little beyond the range of one's experience. Consistent
with this result, subjects who trained on the 30 cm
target showed full generalization to the 15 cm target.
We performed two additional experiments that show that
interleaved trials to the 30 cm target during training
on the 15 cm target can resolve the difference between
the current results and those reported previously.
Ostry DJ, Darainy M, Mattar AAG, Wong J, Gribble PL (2010)
Somatosensory plasticity and motor learning. J Neurosci
30:5384-5393.
Abstract |
PDF
Motor learning
is dependent upon plasticity in motor areas of the
brain, but does it occur in isolation, or does it also
result in changes to sensory systems? We examined
changes to somatosensory function that occur in
conjunction with motor learning. We found that even
after periods of training as brief as 10 min, sensed
limb position was altered and the perceptual change
persisted for 24 h. The perceptual change was reflected
in subsequent movements; limb movements following
learning deviated from the prelearning trajectory by an
amount that was not different in magnitude and in the
same direction as the perceptual shift. Crucially, the
perceptual change was dependent upon motor learning.
When the limb was displaced passively such that subjects
experienced similar kinematics but without learning, no
sensory change was observed. The findings indicate that
motor learning affects not only motor areas of the brain
but changes sensory function as well.
Nasir SM, Ostry DJ (2009) Auditory plasticity and speech
motor learning. Proc Natl Acad Sci U S A 106:20470-20475.
Abstract |
PDF
Is plasticity in
sensory and motor systems linked? Here, in the context
of speech motor learning and perception, we test the
idea sensory function is modified by motor learning and,
in particular, that speech motor learning affects a
speaker's auditory map. We assessed speech motor
learning by using a robotic device that displaced the
jaw and selectively altered somatosensory feedback
during speech. We found that with practice speakers
progressively corrected for the mechanical perturbation
and after motor learning they also showed systematic
changes in their perceptual classification of speech
sounds. The perceptual shift was tied to motor learning.
Individuals that displayed greater amounts of learning
also showed greater perceptual change. Perceptual change
was not observed in control subjects that produced the
same movements, but in the absence of a force field, nor
in subjects that experienced the force field but failed
to adapt to the mechanical load. The perceptual effects
observed here indicate the involvement of the
somatosensory system in the neural processing of speech
sounds and suggest that speech motor learning results in
changes to auditory perceptual function.
Laboissiere R, Lametti DR, Ostry DJ (2009) Impedance control
and its relation to precision in orofacial movement. J
Neurophysiol 102:523-531.
Abstract |
PDF
Speech
production involves some of the most precise and finely
timed patterns of human movement. Here, in the context
of jaw movement in speech, we show that spatial
precision in speech production is systematically
associated with the regulation of impedance and in
particular, with jaw stiffness a measure of resistance
to displacement. We estimated stiffness and also
variability during movement using a robotic device to
apply brief force pulses to the jaw. Estimates of
stiffness were obtained using the perturbed position and
force trajectory and an estimate of what the trajectory
would be in the absence of load. We estimated this
reference trajectory using a new technique based on
Fourier analysis. A moving-average (MA) procedure was
used to estimate stiffness by modeling restoring force
as the moving average of previous jaw displacements. The
stiffness matrix was obtained from the steady state of
the MA model. We applied this technique to data from 31
subjects whose jaw movements were perturbed during
speech utterances and kinematically matched nonspeech
movements. We observed systematic differences in
stiffness over the course of jaw-lowering and
jaw-raising movements that were correlated with measures
of kinematic variability. Jaw stiffness was high and
variability was low early and late in the movement when
the jaw was elevated. Stiffness was low and variability
was high in the middle of movement when the jaw was
lowered. Similar patterns were observed for speech and
nonspeech conditions. The systematic relationship
between stiffness and variability points to the idea
that stiffness regulation is integral to the control of
orofacial movement variability.
Darainy M, Mattar AAG, Ostry DJ (2009) Effects of human arm
impedance on dynamics learning and generalization. J
Neurophysiol 101:3158-3168.
Abstract |
PDF
Previous studies
have demonstrated anisotropic patterns of hand impedance
under static conditions and during movement. Here we
show that the pattern of kinematic error observed in
studies of dynamics learning is associated with this
anisotropic impedance pattern. We also show that the
magnitude of kinematic error associated with this
anisotropy dictates the amount of motor learning and,
consequently, the extent to which dynamics learning
generalizes. Subjects were trained to reach to visual
targets while holding a robotic device that applied
forces during movement. On infrequent trials, the load
was removed and the resulting kinematic error was
measured. We found a strong correlation between the
pattern of kinematic error and the anisotropic pattern
of hand stiffness. In a second experiment subjects were
trained under force-field conditions to move in two
directions: one in which the dynamic perturbation was in
the direction of maximum arm impedance and the
associated kinematic error was low and another in which
the perturbation was in the direction of low impedance
where kinematic error was high. Generalization of
learning was assessed in a reference direction that lay
intermediate to the two training directions. We found
that transfer of learning was greater when training
occurred in the direction associated with the larger
kinematic error. This suggests that the anisotropic
patterns of impedance and kinematic error determine the
magnitude of dynamics learning and the extent to which
it generalizes.
Ito T, Tiede M, Ostry DJ (2009) Somatosensory function in
speech perception. Proc Natl Acad Sci U S A 106:1245-1248.
Abstract |
PDF
Somatosensory
signals from the facial skin and muscles of the vocal
tract provide a rich source of sensory input in speech
production. We show here that the somatosensory system
is also involved in the perception of speech. We use a
robotic device to create patterns of facial skin
deformation that would normally accompany speech
production. We find that when we stretch the facial skin
while people listen to words, it alters the sounds they
hear. The systematic perceptual variation we observe in
conjunction with speech-like patterns of skin stretch
indicates that somatosensory inputs affect the neural
processing of speech sounds and shows the involvement of
the somatosensory system in the perceptual processing in
speech.
Nasir SM, Ostry DJ (2008) Speech motor learning in
profoundly deaf adults. Nat Neurosci 11:1217-1222.
Abstract | PDF
Speech
production, like other sensorimotor behaviors, relies on
multiple sensory inputs-audition, proprioceptive inputs
from muscle spindles and cutaneous inputs from
mechanoreceptors in the skin and soft tissues of the
vocal tract. However, the capacity for intelligible
speech by deaf speakers suggests that somatosensory
input alone may contribute to speech motor control and
perhaps even to speech learning. We assessed speech
motor learning in cochlear implant recipients who were
tested with their implants turned off. A robotic device
was used to alter somatosensory feedback by displacing
the jaw during speech. We found that implant subjects
progressively adapted to the mechanical perturbation
with training. Moreover, the corrections that we
observed were for movement deviations that were
exceedingly small, on the order of millimeters,
indicating that speakers have precise somatosensory
expectations. Speech motor learning is substantially
dependent on somatosensory input.
Darainy M, Ostry DJ (2008) Muscle cocontraction following
dynamics learning. Exp Brain Res 190:153-163.
Abstract |
PDF
Coactivation of
antagonist muscles is readily observed early in motor
learning, in interactions with unstable mechanical
environments and in motor system pathologies. Here we
present evidence that the nervous system uses
coactivation control far more extensively and that
patterns of cocontraction during movement are closely
tied to the specific requirements of the task. We have
examined the changes in cocontraction that follow
dynamics learning in tasks that are thought to involve
finely sculpted feedforward adjustments to motor
commands. We find that, even following substantial
training, cocontraction varies in a systematic way that
depends on both movement direction and the strength of
the external load. The proportion of total activity that
is due to cocontraction nevertheless remains remarkably
constant. Moreover, long after indices of motor learning
and electromyographic measures have reached asymptotic
levels, cocontraction still accounts for a significant
proportion of total muscle activity in all phases of
movement and in all load conditions. These results show
that even following dynamics learning in predictable and
stable environments, cocontraction forms a central part
of the means by which the nervous system regulates
movement.
Andres M, Ostry DJ, Nicol F, Paus T (2008) Time course of
number magnitude interference during grasping. Cortex
44:414-419.
Abstract |
PDF
In the present
study, we recorded the kinematics of grasping movements
in order to measure the possible interference caused by
digits printed on the visible face of the objects to
grasp. The aim of this approach was to test the
hypothesis that digit magnitude processing shares common
mechanisms with object size estimate during grasping. In
the first stages of reaching, grip aperture was found to
be larger consequent to the presentation of digits with
a high value rather than a low one. The effect of digit
magnitude on grip aperture was more pronounced for large
objects. As the hand got closer to the object, the
influence of digit magnitude decreased and grip aperture
progressively reflected the actual size of the object.
We concluded that number magnitude may interact with
grip aperture while programming the grasping movements.
Tremblay S, Houle G, Ostry DJ (2008) Specificity of speech
motor learning. J Neurosci 28:2426-2434.
Abstract |
PDF
The idea that
the brain controls movement using a neural
representation of limb dynamics has been a dominant
hypothesis in motor control research for well over a
decade. Speech movements offer an unusual opportunity to
test this proposal by means of an examination of
transfer of learning between utterances that are to
varying degrees matched on kinematics. If speech
learning results in a generalizable dynamics
representation, then, at the least, learning should
transfer when similar movements are embedded in
phonetically distinct utterances. We tested this idea
using three different pairs of training and transfer
utterances that substantially overlap kinematically. We
find that, with these stimuli, speech learning is highly
contextually sensitive and fails to transfer even to
utterances that involve very similar movements. Speech
learning appears to be extremely local, and the
specificity of learning is incompatible with the idea
that speech control involves a generalized dynamics
representation.
Darainy M, Towhidkhah F, Ostry DJ (2007) Control of hand
impedance under static conditions and during reaching
movement. J Neurophysiol 97:2676-2685.
Abstract |
PDF
It is known that
humans can modify the impedance of the musculoskeletal
periphery, but the extent of this modification is
uncertain. Previous studies on impedance control under
static conditions indicate a limited ability to modify
impedance, whereas studies of impedance control during
reaching in unstable environments suggest a greater
range of impedance modification. As a first step in
accounting for this difference, we quantified the extent
to which stiffness changes from posture to movement even
when there are no destabilizing forces. Hand stiffness
was estimated under static conditions and at the same
position during both longitudinal (near to far) and
lateral movements using a position-servo technique. A
new method was developed to predict the hand "reference"
trajectory for purposes of estimating stiffness. For
movements in a longitudinal direction, there was
considerable counterclockwise rotation of the hand
stiffness ellipse relative to stiffness under static
conditions. In contrast, a small counterclockwise
rotation was observed during lateral movement. In the
modeling studies, even when we used the same modeled
cocontraction level during posture and movement, we
found that there was a substantial difference in the
orientation of the stiffness ellipse, comparable with
that observed empirically. Indeed, the main determinant
of the orientation of the ellipse in our modeling
studies was the movement direction and the muscle
activation associated with movement. Changes in the
cocontraction level and the balance of cocontraction had
smaller effects. Thus even when there is no
environmental instability, the orientation of stiffness
ellipse changes during movement in a manner that varies
with movement direction.
Lametti DR, Houle G, Ostry DJ (2007) Control of movement
variability and the regulation of limb impedance. J
Neurophysiol 98:3516-3524.
Abstract |
PDF
Humans routinely
make movements to targets that have different accuracy
requirements in different directions. Examples extend
from everyday occurrences such as grasping the handle of
a coffee cup to the more refined instance of a surgeon
positioning a scalpel. The attainment of accuracy in
situations such as these might be related to the nervous
system's capacity to regulate the limb's resistance to
displacement, or impedance. To test this idea, subjects
made movements from random starting locations to targets
that had shape-dependent accuracy requirements. We used
a robotic device to assess both limb impedance and
patterns of movement variability just as the subject
reached the target. We show that impedance increases in
directions where required accuracy is high. Independent
of target shape, patterns of limb stiffness are seen to
predict spatial patterns of movement variability. The
nervous system is thus seen to modulate limb impedance
in entirely predictable environments to aid in the
attainment of reaching accuracy.
Mattar AAG, Ostry DJ (2007) Neural averaging in motor
learning. J Neurophysiol 97:220-228.
Abstract |
PDF
The capacity for
skill development over multiple training episodes is
fundamental to human motor function. We have studied the
process by which skills evolve with training by
progressively modifying a series of motor learning tasks
that subjects performed over a 1-mo period. In a series
of empirical and modeling studies, we show that
performance undergoes repeated modification with new
learning. Each in a series of prior training episodes
contributes such that present performance reflects a
weighted average of previous learning. Moreover, we have
observed that the relative weighting of skills learned
wholly in the past changes with time. This suggests that
the neural substrate of skill undergoes modification
after consolidation.
Mattar AAG, Ostry DJ (2007) Modifiability of generalization
in dynamics learning. J Neurophysiol 98:3321-3329.
Abstract |
PDF
Studies on
plasticity in motor function have shown that motor
learning generalizes, such that movements in novel
situations are affected by previous training. It has
been shown that the pattern of generalization for
visuomotor rotation learning changes when training
movements are made to a wide distribution of directions.
Here we have found that for dynamics learning, the shape
of the generalization gradient is not similarly
modifiable by theextent of training within the
workspace. Subjects learned to control a robotic device
during training and we measured how subsequent movements
in a reference direction were affected. Our results show
that as the angular separation between training and test
directions increased, the extent of generalization was
reduced. When training involved multiple targets
throughout the workspace, the extent of generalization
was no greater than following training to the nearest
target alone. Thus a wide range of experience
compensating for a dynamics perturbation provided no
greater benefit than localized training. Instead,
generalization was complete when training involved
targets that bounded the reference direction. This
suggests that broad generalization of dynamics learning
to movements in novel directions depends on
interpolation between instances of localized learning.
Nasir SM, Ostry DJ (2006) Somatosensory precision in speech
production. Curr Biol 16:1918-1923.
Abstract |
PDF
Speech
production is dependent on both auditory and
somatosensory feedback. Although audition may appear to
be the dominant sensory modality in speech production,
somatosensory information plays a role that extends from
brainstem responses to cortical control. Accordingly,
the motor commands that underlie speech movements may
have somatosensory as well as auditory goals. Here we
provide evidence that, independent of the acoustics,
somatosensory information is central to achieving the
precision requirements of speech movements. We were able
to dissociate auditory and somatosensory feedback by
using a robotic device that altered the jaw's motion
path, and hence proprioception, without affecting speech
acoustics. The loads were designed to target either the
consonant- or vowel-related portion of an utterance
because these are the major sound categories in speech.
We found that, even in the absence of any effect on the
acoustics, with learning subjects corrected to an equal
extent for both kinds of loads. This finding suggests
that there are comparable somatosensory precision
requirements for both kinds of speech sounds. We provide
experimental evidence that the neural control of
stiffness or impedance--the resistance to
displacement--provides for somatosensory precision in
speech production.
Darainy M, Malfait N, Towhidkhah F, Ostry DJ (2006) Transfer
and durability of acquired patterns of human arm stiffness.
Exp Brain Res 170:227-237.
Abstract |
PDF
We used a
robotic device to test the idea that impedance control
involves a process of learning or adaptation that is
acquired over time and permits the voluntary control of
the pattern of stiffness at the hand. The tests were
conducted in statics. Subjects were trained over the
course of three successive days to resist the effects of
one of three different kinds of mechanical loads, single
axis loads acting in the lateral direction, single axis
loads acting in the forward/backward direction and
isotropic loads that perturbed the limb in eight
directions about a circle. We found that subjects in
contact with single axis loads voluntarily modified
their hand stiffness orientation such that changes to
the direction of maximum stiffness mirrored the
direction of applied load. In the case of isotropic
loads, a uniform increase in endpoint stiffness was
observed. Using a physiologically realistic model of
two-joint arm movement, the experimentally determined
pattern of impedance change could be replicated by
assuming that coactivation of elbow and double joint
muscles was independent of coactivation of muscles at
the shoulder. Moreover, using this pattern of
coactivation control we were able to replicate an
asymmetric pattern of rotation of the stiffness ellipse
that was observed empirically. The present findings are
consistent with the idea that arm stiffness is
controlled through the use of at least two independent
cocontraction commands.
Shiller DM, Houle G, Ostry DJ (2005) Voluntary control of
human jaw stiffness. J Neurophysiol 94:2207-2217.
Abstract
|
PDF
Recent studies
of human arm movement have suggested that the control of
stiffness may be important both for maintaining
stability and for achieving differences in movement
accuracy. In the present study, we have examined the
voluntary control of postural stiffness in 3D in the
human jaw. The goal is to address the possible role of
stiffness control in both stabilizing the jaw and in
achieving the differential precision requirements of
speech sounds. We previously showed that patterns of
kinematic variability in speech are systematically
related to the stiffness of the jaw. If the nervous
system uses stiffness control as a means to regulate
kinematic variation in speech, it should also be
possible to show that subjects can voluntarily modify
jaw stiffness. Using a robotic device, a series of force
pulses was applied to the jaw to elicit changes in
stiffness to resist displacement. Three orthogonal
directions and three magnitudes of forces were tested.
In all conditions, subjects increased the magnitude of
jaw stiffness to resist the effects of the applied
forces. Apart from the horizontal direction, greater
increases in stiffness were observed when larger forces
were applied. Moreover, subjects differentially
increased jaw stiffness along a vertical axis to
counteract disturbances in this direction. The observed
changes in the magnitude of stiffness in different
directions suggest an ability to control the pattern of
stiffness of the jaw. The results are interpreted as
evidence that jaw stiffness can be adjusted voluntarily,
and thus may play a role in stabilizing the jaw and in
controlling movement variation in the orofacial system.
Malfait N, Gribble PL, Ostry DJ (2005) Generalization of
motor learning based on multiple field exposures and local
adaptation. J Neurophysiol 93:3327-3338.
Abstract
|
PDF
Previous studies
have used transfer of learning over workspace locations
as a means to determine whether subjects code
information about dynamics in extrinsic or intrinsic
coordinates. Transfer has been observed when the torque
associated with joint displacement is similar between
workspace locations rather than when the mapping between
hand displacement and force is preserved which is
consistent with muscle- or joint based encoding. In the
present study, we address the generality of an intrinsic
coding of dynamics and examine how generalization occurs
when the pattern of torques varies over the workspace.
In two initial experiments, we examined transfer of
learning when the direction of a force field was fixed
relative to an external frame of reference. While there
were no beneficial effects of transfer following
training at a single location (Experiment 1 and 2),
excellent performance was observed at the center of the
workspace following training at two lateral locations
(Experiment 2). Experiment 3 and associated simulations
assessed the characteristics of this generalization. In
these studies, we examined the patterns of transfer
observed following adaptation to force fields that were
composed of two subfields that acted in opposite
directions. The experimental and simulated data are
consistent with the idea that information about dynamics
is encoded in intrinsic coordinates. The nervous system
generalizes dynamics learning by interpolating between
sets of control signals, each locally adapted to
different patterns of torques.
Della-Maggiore V, Malfait N, Ostry DJ, Paus T (2004)
Stimulation of the posterior parietal cortex interferes with
arm trajectory adjustments during the learning of new
dynamics. J Neurosci 24:9971-9976.
Abstract
|
PDF
Substantial
neurophysiological evidence points to the posterior
parietal cortex (PPC) as playing a key role in the
coordinate transformation necessary for visually guided
reaching. Our goal was to examine the role of PPC in the
context of learning new dynamics of arm movements. We
assessed this possibility by stimulating PPC with
transcranial magnetic stimulation (TMS) while subjects
learned to make reaching movements with their right hand
in a velocity-dependent force field. We reasoned that,
if PPC is necessary to adjust the trajectory of the arm
as it interacts with a novel mechanical system,
interfering with the functioning of PPC would impair
adaptation. Single pulses of TMS were applied over the
left PPC 40 msec after the onset of movement during
adaptation. As a control, another group of subjects was
stimulated over the visual cortex. During early stages
of learning, the magnitude of the error (measured as the
deviation of the hand paths) was similar across groups.
By the end of the learning period, however, error
magnitudes decreased to baseline levels for controls but
remained significantly larger for the group stimulated
over PPC. Our findings are consistent with a role of PPC
in the adjustment of motor commands necessary for
adapting to a novel mechanical environment.
Darainy M, Malfait N, Gribble PL, Towhidkhah F, Ostry DJ
(2004) Learning to control arm stiffness under static
conditions. J Neurophysiol 92:3344-3350.
Abstract
|
PDF
We used a
robotic device to test the idea that impedance control
involves a process of learning or adaptation that is
acquired over time and permits the voluntary control of
the pattern of stiffness at the hand. The tests were
conducted in statics. Subjects were trained over the
course of three successive days to resist the effects of
one of three different kinds of mechanical loads, single
axis loads acting in the lateral direction, single axis
loads acting in the forward/backward direction and
isotropic loads that perturbed the limb in eight
directions about a circle. We found that subjects in
contact with single axis loads voluntarily modified
their hand stiffness orientation such that changes to
the direction of maximum stiffness mirrored the
direction of applied load. In the case of isotropic
loads, a uniform increase in endpoint stiffness was
observed. Using a physiologically realistic model of
two-joint arm movement, the experimentally determined
pattern of impedance change could be replicated by
assuming that coactivation of elbow and double joint
muscles was independent of coactivation of muscles at
the shoulder. Moreover, using this pattern of
coactivation control we were able to replicate an
asymmetric pattern of rotation of the stiffness ellipse
that was observed empirically. The present findings are
consistent with the idea that arm stiffness is
controlled through the use of at least two independent
cocontraction commands.
Malfait N, Ostry DJ (2004) Is interlimb transfer of
force-field adaptation a "cognitive" response to the sudden
introduction of load? J Neurosci 24:8084-8089.
Abstract
|
PDF
Recently,
Shadmehr and colleagues (Criscimagna-Hemminger et al.
2003) reported a pattern of generalization of
force-field adaptation between arms that differs from
the pattern that occurs across different configurations
of the same arm. While the intralimb pattern of
generalization points to an intrinsic encoding of
dynamics, the interlimb transfer described by these
authors indicates that information about force is
represented in a frame of reference external to the
body. In the present study, subjects adapted to a
viscous curl-field in two experimental conditions. In
one condition, the field was introduced suddenly and
produced clear deviations in hand paths; in the second
condition, the field was introduced gradually so that at
no point during the adaptation process could subjects
observe or had to correct for a substantial kinematic
error. In the first case, a pattern of interlimb
transfer consistent with Criscimagna-Hemminger et al.
was observed, whereas no transfer of learning between
limbs occurred in the second condition. The findings
suggest that there is limited transfer of fine
compensatory force adjustment between limbs. Transfer
when it does occur may be largely the results of a
"cognitive" strategy that arises as a result of the
sudden introduction of load and associated kinematic
error.
Petitto LA, Holowka S, Sergio LE, Levy B, Ostry DJ (2004)
Baby hands that move to the rhythm of language: hearing
babies acquiring sign languages babble silently on the
hands. Cognition 93:43-73.
Abstract
|
PDF
The "ba, ba, ba"
sound universal to babies' babbling around 7 months
captures scientific attention because it provides
insights into the mechanisms underlying language
acquisition and vestiges of its evolutionary origins.
Yet the prevailing mystery is what is the biological
basis of babbling, with one hypothesis being that it is
a non-linguistic motoric activity driven largely by the
baby's emerging control over the mouth and jaw, and
another being that it is a linguistic activity
reflecting the babies' early sensitivity to specific
phonetic-syllabic patterns. Two groups of hearing babies
were studied over time (ages 6, 10, and 12 months),
equal in all developmental respects except for the
modality of language input (mouth versus hand): three
hearing babies acquiring spoken language (group 1:
"speech-exposed") and a rare group of three hearing
babies acquiring sign language only, not speech (group
2: "sign-exposed"). Despite this latter group's exposure
to sign, the motoric hypothesis would predict similar
hand activity to that seen in speech-exposed hearing
babies because language acquisition in sign-exposed
babies does not involve the mouth. Using innovative
quantitative Optotrak 3-D motion-tracking technology,
applied here for the first time to study infant language
acquisition, we obtained physical measurements similar
to a speech spectrogram, but for the hands. Here we
discovered that the specific rhythmic frequencies of the
hands of the sign-exposed hearing babies differed
depending on whether they were producing linguistic
activity, which they produced at a low frequency of
approximately 1 Hz, versus non-linguistic activity,
which they produced at a higher frequency of
approximately 2.5 Hz the identical class of hand
activity that the speech-exposed hearing babies produced
nearly exclusively. Surprisingly, without benefit of the
mouth, hearing sign-exposed babies alone babbled
systematically on their hands. We conclude that babbling
is fundamentally a linguistic activity and explain why
the differentiation between linguistic and
non-linguistic hand activity in a single manual modality
(one distinct from the human mouth) could only have
resulted if all babies are born with a sensitivity to
specific rhythmic patterns at the heart of human
language and the capacity to use them.
Ostry DJ, Feldman AG (2003) A critical evaluation of the
force control hypothesis in motor control. Exp Brain Res
221:275-288.
Abstract
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PDF
The ability to
formulate explicit mathematical models of motor systems
has played a central role in recent progress in motor
control research. As a result of these modeling efforts
and in particular the incorporation of concepts drawn
from control systems theory, ideas about motor control
have changed substantially. There is growing emphasis on
motor learning and particularly on predictive or
anticipatory aspects of control that are related to the
neural representation of dynamics. Two ideas have become
increasingly prominent in mathematical modeling of motor
function forward internal models and inverse dynamics.
The notion of forward internal models which has drawn
from work in adaptive control arises from the
recognition that the nervous system takes account of
dynamics in motion planning. Inverse dynamics, a
complementary way of adjusting control signals to deal
with dynamics, has proved a simple means to establish
the joint torques necessary to produce desired
movements. In this paper, we review the force control
formulation in which inverse dynamics and forward
internal models play a central role. We present evidence
in its favor and describe its limitations. We note that
inverse dynamics and forward models are potential
solutions to general problems in motor control how the
nervous system establishes a mapping between desired
movements and associated control signals, and how
control signals are adjusted in the context of motor
learning, dynamics and loads. However, we find little
empirical evidence that specifically supports the
inverse dynamics or forward internal model proposals per
se. We further conclude that the central idea of the
force control hypothesis that control levels operate
through the central specification of forces is flawed.
This is specifically evident in the context of attempts
to incorporate physiologically realistic muscle and
reflex mechanisms into the force control model. In
particular, the formulation offers no means to shift
between postures without triggering resistance due to
postural stabilizing mechanisms.
Tremblay S, Shiller DM,Ostry DJ (2003) Somatosensory basis
of speech production. Nature 423:866-869.
Abstract
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PDF
The hypothesis
that speech goals are defined acoustically and
maintained by auditory feedback is a central idea in
speech production research. An alternative proposal is
that speech production is organized in terms of control
signals that subserve movements and associated
vocal-tract configurations. Indeed, the capacity for
intelligible speech by deaf speakers suggests that
somatosensory inputs related to movement play a role in
speech production-but studies that might have documented
a somatosensory component have been equivocal. For
example, mechanical perturbations that have altered
somatosensory feedback have simultaneously altered
acoustics. Hence, any adaptation observed under these
conditions may have been a consequence of acoustic
change. Here we show that somatosensory information on
its own is fundamental to the achievement of speech
movements. This demonstration involves a dissociation of
somatosensory and auditory feedback during speech
production. Over time, subjects correct for the effects
of a complex mechanical load that alters jaw movements
(and hence somatosensory feedback), but which has no
measurable or perceptible effect on acoustic output. The
findings indicate that the positions of speech
articulators and associated somatosensory inputs
constitute a goal of speech movements that is wholly
separate from the sounds produced.
Malfait N, Shiller DM, Ostry DJ (2002) Transfer of motor
learning across arm configurations. J Neurosci 22:9656-9660.
Abstract
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PDF
It has been
suggested that learning of new dynamics occurs in
intrinsic coordinates. However, it has also been
suggested that elements that encode hand velocity and
hence act in an extrinsic frame of reference play a role
in the acquisition of dynamics. In order to reconcile
claims regarding the coordinate system involved in the
representation of dynamics, we have used a procedure
involving the transfer of force-field learning between
two workspace locations. Subjects made point-to-point
movements while holding a two-link manipulandum.
Subjects were first trained to make movements in a
single direction at the left of the workspace. They were
then tested for transfer of learning at the right of the
workspace. Two groups of subjects were defined. For
subjects in Group J, movements at the left and right
workspace locations were matched in terms of joint
displacements. For subjects in Group H, movements in the
two locations had the same hand displacements. Workspace
locations were chosen such that for Group J, the paths
(for training and testing) that were identical in joint
space were orthogonal in hand space. Subjects in Group J
showed good transfer between workspace locations,
whereas subjects in Group H showed poor transfer. The
results are in agreement with the idea that new dynamics
are encoded in intrinsic coordinates and that this
learning has a limited range of generalization across
joint velocities.
Shiller DM, Laboissiere R, Ostry DJ (2002) The relationship
between jaw stiffness and kinematic variability in speech. J
Neurophysiol 88:2329-2340.
Abstract
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PDF
Humans produce
speech by controlling a complex biomechanical apparatus
to achieve desired speech sounds. We show here that
kinematic variability in speech may be influenced by
patterns of jaw stiffness. A robotic device was used to
deliver mechanical perturbations to the jaw to quantify
its stiffness in the mid-sagittal plane. Measured jaw
stiffness was anisotropic. Stiffness was greatest along
a protrusion-retraction axis and least in the direction
of jaw raising and lowering. Consistent with the idea
that speech movements reflect directional asymmetries in
jaw stiffness, kinematic variability during speech
production was found to be high in directions in which
stiffness is low and vice versa. In addition, for higher
jaw elevations, stiffness was greater and kinematic
variability was less. The observed patterns of kinematic
variability were not specific to speech similar patterns
appeared in speech and nonspeech movements. The
empirical patterns of stiffness were replicated by using
a physiologically based model of the jaw. The simulation
studies support the idea that the pattern of jaw
stiffness is affected by musculo-skeletal geometry and
muscle-force-generating abilities with jaw geometry
being the primary determinant of the orientation of the
stiffness ellipse.
Shiller DM, Ostry DJ, Gribble PL, Laboissiere R (2001)
Compensation for the effects of head acceleration on jaw
movement in speech. J Neurosci 21:6447-6456.
Abstract
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PDF
Recent studies
have demonstrated the ability of subjects to adjust the
control of limb movements to counteract the effects of
self-generated loads. The degree to which subjects
change control signals to compensate for these loads is
a reflection of the extent to which forces affecting
movement are represented in motion planning. Here, we
have used empirical and modeling studies to examine
whether the nervous system compensates for loads acting
on the jaw during speech production. As subjects walk,
loads to the jaw vary with the direction and magnitude
of head acceleration. We investigated the patterns of
jaw motion resulting from these loads both in locomotion
alone and when locomotion was combined with speech
production. In locomotion alone, jaw movements were
shown to vary systematically in direction and magnitude
in relation to the acceleration of the head. In
contrast, when locomotion was combined with speech,
variation in jaw position during both consonant and
vowel production was substantially reduced. Overall, we
have demonstrated that the magnitude of load associated
with head acceleration during locomotion is sufficient
to produce a systematic change in the position of the
jaw. The absence of variation in jaw position during
locomotion with speech is thus consistent with the idea
that in speech, the control of jaw motion is adjusted in
a predictive manner to offset the effects of head
acceleration.
Petitto LA, Holowka S, Sergio LE, Ostry DJ (2001) Language
rhythms in baby hand movements. Nature 413:35-36.
Abstract |
PDF
Suzuki M, Shiller DM, Gribble PL, Ostry DJ (2001)
Relationship between cocontraction, movement kinematics and
phasic muscle activity in single-joint arm movement. Exp
Brain Res 140:171-181.
Abstract
| PDF
Patterns of
muscle coactivation provide a window into mechanisms
of limb stabilization. In the present paper we have
examined muscle coactivation in single-joint elbow and
single-joint shoulder movements and explored its
relationship to movement velocity and amplitude, as
well as phasic muscle activation patterns. Movements
were produced at several speeds and different
amplitudes, and muscle activity and movement
kinematics were recorded. Tonic levels of
electromyographic (EMG) activity following movement
provided a measure of muscle cocontraction. It was
found that coactivation following movement increased
with maximum joint velocity at each of two amplitudes.
Phasic EMG activity in agonist and antagonist muscles
showed a similar correlation that was observable even
during the first 30 ms of muscle activation. All
subjects but one showed statistically significant
correlations on a trial-by-trial basis between tonic
and phasic activity levels, including the phasic
activity measure taken at the initiation of movement.
Our findings provide direct evidence that muscle
coactivation varies with movement velocity. The data
also suggest that cocontraction is linked in a simple
manner to phasic muscle activity. The similarity in
the patterns of tonic and phasic activation suggests
that the nervous system may use a simple strategy to
adjust coactivation and presumably limb impedance in
association with changes in movement speed. Moreover,
since the pattern of tonic activity varies with the
first 30 ms of phasic activity, the control of
cocontraction may be established prior to movement
onset.
Ostry DJ, Romo R (2001) Tactile shape processing. Neuron
31:173-174.
Abstract
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PDF
Neuroimaging
techniques may aid in the identification of areas of the
human brain that are involved in tactile shape
perception. Bodegard et al. (2001) relate differences in
the properties of tactile stimuli to differences in
areas of cortical activation to infer tactile processing
in the somatosensory network.
Gribble PL, Ostry DJ (2000) Compensation for loads during
arm movements using equilibrium-point control. Exp Brain Res
135:474-482.
Abstract
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PDF
A significant
problem in motor control is how information about
movement error is used to modify control signals to
achieve desired performance. A potential source of
movement error and one that is readily controllable
experimentally relates to limb dynamics and associated
movement-dependent loads. In this paper, we have used a
position control model to examine changes to control
signals for arm movements in the context of
movement-dependent loads. In the model, based on the
equilibrium-point hypothesis, equilibrium shifts are
adjusted directly in proportion to the positional error
between desired and actual movements. The model is used
to simulate multi-joint movements in the presence of
both "internal" loads due to joint interaction torques,
and externally applied loads resulting from
velocity-dependent force fields. In both cases it is
shown that the model can achieve close correspondence to
empirical data using a simple linear adaptation
procedure. An important feature of the model is that it
achieves compensation for loads during movement without
the need for either coordinate transformations between
positional error and associated corrective forces, or
inverse dynamics calculations.
Gribble PL, Ostry DJ (1999) Compensation for interaction
torques during single- and multijoint limb movements. J
Neurophysiol 82:2310-2326.
Abstract
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PDF
During
multi-joint limb movements such as reaching, rotational
forces arise at one joint due to the motions of limb
segments about other joints. We report the results of
three experiments in which we assessed the extent to
which control signals to muscles are adjusted to
counteract these ``interaction torques''. Human subjects
performed single- and multi-joint pointing movements
involving shoulder and elbow motion, and movement
parameters related to the magnitude and direction of
interaction torques were systematically manipulated. We
examined electromyographic (EMG) activity of shoulder
and elbow muscles, and specifically, the relationship
between EMG activity and joint interaction torque. A
first set of experiments examined single-joint
movements. During both single-joint elbow (Experiment 1)
and shoulder (Experiment 2) movements, phasic EMG
activity was observed in muscles spanning the stationary
joint (shoulder muscles in Experiment 1 and elbow
muscles in Experiment 1). This muscle activity preceded
movement, and varied in amplitude with the magnitude of
upcoming interaction torque (the load resulting from
motion of the non-stationary limb segment). In a third
experiment, subjects performed multi-joint movements
involving simultaneous motion at the shoulder and elbow.
Movement amplitude and velocity at one joint were held
constant, while the direction of movement about the
other joint was varied. When the direction of elbow
motion was varied (flexion vs extension) and shoulder
kinematics were held constant, EMG activity in shoulder
muscles varied depending on the direction of elbow
motion (and hence the sign of the interaction torque
arising at the shoulder). Similarly, EMG activity in
elbow muscles varied depending on the direction of
shoulder motion, for movements in which elbow kinematics
were held constant. The results from all three
experiments support the idea that central control
signals to muscles are adjusted, in a predictive manner,
to compensate for interaction torques loads arising at
one joint which depend on motion about other joints.
Shiller DM, Ostry DJ, Gribble PL (1999) Effects of
gravitational load on jaw movements in speech. J Neurosci
19:9073-9080.
Abstract
|
PDF
External loads
arising due to the orientation of body segments relative
to gravity can affect the achievement of movement goals.
The degree to which subjects adjust control signals to
compensate for these loads is a reflection of the extent
to which forces affecting motion are represented
neurally. In the present study we assessed whether
subjects, when speaking, compensate for loads due to the
orientation of the head relative to gravity. We used a
mathematical model of the jaw to predict the effects of
control signals that are not adjusted for changes to
head orientation. The simulations predicted a systematic
change in sagittal plane jaw orientation and horizontal
position resulting from changes to the orientation of
the head. We conducted an empirical study in which
subjects were tested under the same conditions. With one
exception, empirical results were consistent with the
simulations. In both simulation and empirical studies,
the jaw was rotated closer to occlusion and translated
in an anterior direction when the head was in the prone
orientation. When the head was in the supine orienation,
the jaw was rotated away from occlusion. The findings
suggest that the nervous system does not completely
compensate for changes in head orientation relative to
gravity. A second study was conducted to assess possible
changes in acoustical patterns due to changes in head
orientation. The frequencies of the first (F1) and
second (F2) formants associated with the steady-state
portion of vowels were measured. As in the kinematic
study, systematic differences in the values of F1 and F2
were observed with changes in head orientation. Thus the
acoustical analysis further supports the conclusion that
control signals are not completely adjusted to offset
forces arising due to changes in orientation.
Gribble PL, Ostry DJ (1998) Independent coactivation of
shoulder and elbow muscles. Exp Brain Res 123:355-360.
Abstract
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PDF
The aim of this
study was to examine the possibility of independent
muscle coactivation at the shoulder and elbow. Subjects
performed rapid point-to-point movements in a horizontal
plane, from different initial limb configurations to a
single target. EMG activity was measured from flexor and
extensor muscles that act at the shoulder (pectoralis
clavicular head and posterior deltoid) and elbow (biceps
long head and triceps lateral head) and flexor and
extensor muscles that act at both joints (biceps short
head and triceps long head). Muscle coactivation was
assessed by measuring tonic levels of electromyographic
(EMG) activity after limb position stabilized following
movement end. It was observed that tonic EMG levels
following movements to the same target varied as a
function of the amplitude of shoulder and elbow motion.
Moreover, for the movements tested here, the
coactivation of shoulder and elbow muscles was found to
be independent tonic EMG activity of shoulder muscles
increased in proportion to shoulder movement, but was
unrelated to elbow motion, whereas elbow and
double-joint muscle coactivation varied with the
amplitude of elbow movement, and were uncorrelated with
shoulder motion. In addition, tonic EMG levels were
higher for movements in which the shoulder and elbow
rotated in the same direction, as compared to those in
which the joints rotated in opposite directions. In this
respect, muscle coactivation may reflect a simple
strategy to compensate for forces introduced by
multijoint limb dynamics.
Feldman AG, Ostry DJ, Levin MF, Gribble PL, Mitnitski A
(1998) Recent tests of the equilibrium point hypothesis.
Motor Control 2:189-205.
Abstract
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PDF
The lambda model
of the equilibrium-point hypothesis (Feldman &
Levin, 1995) is an approach to motor control which, like
physics, is based on a logical system coordinating
empirical data. The model has gone through an
interesting period. On one hand, several nontrivial
predictions of the model have been successfully verified
in recent studies. In addition, the explanatory and
predictive capacity of the model has been enhanced by
its extension to multimuscle and multijoint systems. On
the other hand, claims have recently appeared suggesting
that the model should be abandoned. The present paper
focuses on these claims and concludes that they are
unfounded. Much of the experimental data that have been
used to reject the model are actually consistent with
it.
Gribble PL, Ostry DJ, Sanguineti V, Laboissiere R (1998) Are
complex control signals required for human arm movement? J
Neurophysiol 79:1409-1424.
Abstract
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PDF
It has been
proposed that the control signals underlying voluntary
human arm movement have a "complex" non-monotonic
time-varying form, and a number of empirical findings
have been offered in support of this idea (Gomi and
Kawato, 1996, Latash and Gottlieb, 1991). In this paper
we address three such findings using a model of
two-joint arm motion based on the lambda version of the
equilibrium-point hypothesis. The model includes six
one- and two-joint muscles, reflexes, modeled control
signals, muscle properties and limb dynamics. First, we
address the claim that "complex" equilibrium
trajectories are required in order to account for
non-monotonic joint impedance patterns observed during
multi-joint movement (Gomi and Kawato, 1996). Using
constant-rate shifts in the neurally specified
equilibrium of the limb, and constant cocontraction
commands, we obtain patterns of predicted joint
stiffness during simulated multi-joint movements which
match the non-monotonic patterns reported empirically.
We then use the algorithm proposed by Gomi and Kawato
(1996) to compute a hypothetical equilibrium trajectory
from simulated stiffness, viscosity and limb kinematics.
Like that reported by Gomi and Kawato (1996), the
resulting trajectory was non-monotonic, first leading
then lagging the position of the limb. Second, we
address the claim that high levels of stiffness are
required to generate rapid single-joint movements when
simple equilibrium shifts are used. We compare empirical
measurements of stiffness during rapid single-joint
movements (Bennett, 1993) with the predicted stiffness
of movements generated using constant-rate equilibrium
shifts and constant cocontraction commands. Single-joint
movements are simulated at a number of speeds, and the
procedure used by Bennett (1993) to estimate stiffness
is followed. We show that when the magnitude of the
cocontraction command is scaled in proportion to
movement speed, simulated joint stiffness varies with
movement speed in a manner comparable to that reported
by Bennett (1993). Third, we address the related claim
that non-monotonic equilibrium shifts are required to
generate rapid single-joint movements. Using
constant-rate equilibrium shifts and constant
cocontraction commands, rapid single-joint movements are
simulated in the presence of external torques. We use
the procedure reported by Latash and Gottlieb (1991) to
compute hypothetical equilibrium trajectories from
simulated torque and angle measurements during movement.
As in Latash and Gottlieb (1991), a non-monotonic
function is obtained, even though the control signals
used in the simulations are constant-rate changes in the
equilibrium position of the limb. Differences between
the "simple" equilibrium trajectory proposed in the
present paper and those which are derived from the
procedures used by Gomi and Kawato (1996) and Latash and
Gottlieb (1991) arise from their use of simplified
models of force-generation.
Sanguineti V, Laboissiere R, Ostry DJ (1998) A dynamic
biomechanical model for neural control of speech production.
J Acoust Soc Am 103:1615-1627.
Abstract
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PDF
A model of the
midsagittal plane motion of the tongue, jaw, hyoid bone,
and larynx is presented, based on the lambda version of
equilibrium point hypothesis. The model includes muscle
properties and realistic geometrical arrangement of
muscles, modeled neural inputs and reflexes, and
dynamics of soft tissue and bony structures. The focus
is on the organization of control signals underlying
vocal tract motions and on the dynamic behavior of
articulators. A number of muscle synergies or "basic
motions" of the system are identified. In particular, it
is shown that systematic sources of variation in an
x-ray data base of midsagittal vocal tract motions can
be accounted for, at the muscle level, with six
independent commands, each corresponding to a direction
of articulator motion. There are two commands for the
jaw, (corresponding to sagittal plane jaw rotation and
jaw protrusion), one command controlling larynx height,
and three commands for the tongue, (corresponding to
forward and backward motion of the tongue body, arching
and flattening of the tongue dorsum, and motion of the
tongue tip). It is suggested that all movements of the
system can be approximated as linear combinations of
such basic motions. In other words, individual movements
and sequences of movements can be accounted for by a
simple additive control model. The dynamics of
individual commands are also assessed. It is shown that
the dynamic effects are not neglectable in speechlike
movements because of the different dynamic behaviors of
soft and bony structures.
Guiard-Marigny T, Ostry DJ (1997) A system for
three-dimensional visualization of human jaw motion in
speech. J Speech Lang Hear Res 40:1118-1121.
Abstract
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PDF
With the
development of precise three dimensional motion
measurement systems and powerful computers for three
dimensional graphical visualization, it is possible to
record and fully reconstruct human jaw motion. In this
paper, we describe a visualization system for displaying
three dimensional jaw movements in speech. The system is
designed to take as input jaw motion data obtained from
one or multi-dimensional recording systems. In the
present application, kinematic records of jaw motion
were recorded using an optoelectronic measurement system
(Optotrak). The corresponding speech signal was recorded
using an analog input channel. The three orientation
angles and three positions which describe the motion of
the jaw as a rigid skeletal structure were derived from
the empirical measurements. These six kinematic
variables, which in mechanical terms account fully for
jaw motion kinematics, act as inputs that drive a
real-time three dimensional animation of a skeletal jaw
and upper skull. The visualization software enables the
user to view jaw motion from any orientation and to
change the viewpoint during the course of an utterance.
Selected portions of an utterance may be re-played and
the speed of the visual display may be varied. The user
may also display, along with the audio track, individual
kinematic degrees of freedom or several degrees of
freedom in combination. The system is presently being
used as an educational tool and for research into
audio-visual speech recognition.
Ostry DJ, Vatikiotis-Bateson E, Gribble PL (1997) An
examination of the degrees of freedom of human jaw motion in
speech and mastication. J Speech Lang Hear Res 40:1341-1351.
Abstract
|
PDF
The kinematics
of human jaw movements were assessed in terms of the
three orientation angles and three positions that
characterize the motion of the jaw as a rigid body. The
analysis focused on the identification of the jaw's
independent movement dimensions, and was based on an
examination of jaw motion paths that were plotted in
various combinations of linear and angular coordinate
frames. Overall, both behaviors were characterized by
independent motion in four degrees of freedom. In
general, when jaw movements were plotted to show
orientation in the sagittal plane as a function of
horizontal position, relatively straight paths were
observed. In speech, the slopes and intercepts of these
paths varied depending on the phonetic material. The
vertical position of the jaw was observed to shift up or
down so as to displace the overall form of the sagittal
plane motion path of the jaw. Yaw movements were small
but independent of pitch, vertical and horizontal
position. In mastication, the slope and intercept of the
relationship between pitch and horizontal position were
affected by the type of food and its size. However, the
range of variation was less than that observed in
speech. When vertical jaw position was plotted as a
function of horizontal position, the basic form of the
path of the jaw was maintained but could be shifted
vertically. In general, larger bolus diameters were
associated with lower jaw positions throughout the
movement. The timing of pitch and yaw motion differed.
The most common pattern involved changes in pitch angle
during jaw opening followed by a phase predominated by
lateral motion (yaw). Thus, in both behaviors there was
evidence of independent motion in pitch, yaw, horizontal
position and vertical position. This is consistent with
the idea that motions in these degrees of freedom are
independently controlled.
Ostry DJ, Gribble PL, Levin MF, Feldman AG (1997) Phasic and
tonic stretch reflexes in muscles with few muscles spindles:
human jaw-opener muscles. Exp Brain Res 116:299-308.
Abstract
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PDF
We investigated
phasic and tonic stretch reflexes in human jaw opener
muscles, which have few, if any, muscle spindles. Jaw
unloading reflexes were recorded for both opener and
closer muscles. Surface electromyographic (EMG) activity
was obtained from left and right digastric and
superficial masseter muscles, and jaw orientation and
torques were recorded. Unloading of jaw opener muscles
elicited a short-latency decrease in EMG activity
(averaging 20 ms) followed by a short duration silent
period in these muscles and sometimes a short burst of
activity in their antagonists. Similar behavior in
response to unloading was observed for spindle-rich jaw
closer muscles although the latency of the silent period
was statistically shorter than that observed for jaw
opener muscles (averaging 13 ms). Control studies
suggest that the jaw opener reflex was not due to inputs
from either cutaneous or periodontal mechanoreceptors.
In the unloading response of the jaw openers, the tonic
level of EMG activity observed after transition to the
new jaw orientation was monotonically related to the
residual torque and orientation. This is consistent with
the idea that the tonic stretch reflex may mediate the
change in muscle activation. In addition, the values of
the static net joint torque and jaw orientation after
the dynamic phase of unloading were related by a
monotonic function resembling the invariant
characteristic recorded in human limb joints. The
torque-angle characteristics associated with different
initial jaw orientations were similar in shape but
spatially shifted, consistent with the idea that
voluntary changes in jaw orientation may be associated
with a change in a single parameter, which may be
identified as the threshold of the tonic stretch reflex.
It is suggested that functionally significant phasic and
tonic stretch reflexes may not be mediated exclusively
by muscle spindle afferents. Thus, the hypothesis that
central modifications in the threshold of the tonic
stretch reflex underlie the control of movement may be
applied to the jaw system.
Gribble PL, Ostry DJ (1996) Origins of the power law
relation between movement velocity and curvature: modeling
the effects of muscle mechanics and limb dynamics. J
Neurophysiol 76:2853-2860.
Abstract
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PDF
1. When subjects
trace patterns such as ellipses, the instantaneous
velocity of movements is related to the instantaneous
curvature of the trajectories according to a power law
movements tend to slow down when curvature is high and
speed up when curvature is low. It has been proposed
that this relationship is centrally planned. 2. The
arm's muscle properties and dynamics can significantly
affect kinematics. Even under isometric conditions,
muscle mechanical properties can affect the development
of muscle forces and torques. Without a model which
accounts for these effects, it is difficult to
distinguish between kinematic patterns which are
attributable to central control and patterns which arise
due to dynamics and muscle properties and are not
represented in the underlying control signals. 3. In
this paper we address the nature of the control signals
that underlie movements which obey the power law. We use
a numerical simulation of arm movement control based on
the lambda version of the equilibrium-point hypothesis.
We demonstrate that simulated elliptical and circular
movements, and elliptical force trajectories generated
under isometric conditions, obey the power law even
though there was no relation between curvature and speed
in the modeled control signals. 4. We suggest that limb
dynamics and muscle mechanics specifically, the
spring-like properties of muscles can contribute
significantly to the emergence of the power law
relationship in kinematics. Thus without a model that
accounts for these effects, care must be taken when
making inferences about the nature of neural control.
Ramsay JO, Munhall KG, Gracco VL, Ostry DJ (1996) Functional
data analyses of lip motion. J Acoust Soc Am 99:3718-3727.
Abstract
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PDF
The vocal
tract's motion during speech is a complex patterning of
the movement of many different articulators according to
many different time functions. Understanding this myriad
of gestures is important to a number of different
disciplines including automatic speech recognition,
speech and language pathologies, speech motor control,
and experimental phonetics. Central issues are the
accurate description of the shape of the vocal tract and
determining how each articulator contributes to this
shape. A problem facing all of these research areas is
how to cope with the multivariate data from speech
production experiments. In this paper techniques are
described that provide useful tools for describing
multivariate functional data such as the measurement of
speech movements. The choice of data analysis procedures
has been motivated by the need to partition the
articulator movement in various ways: end effects
separated from shape effects, partitioning of syllable
effects, and the splitting of variation within an
articulator site from variation from between sites. The
techniques of functional data analysis seem admirably
suited to the analyses of phenomena such as these.
Familiar multivariate procedures such as analysis of
variance and principal components analysis have their
functional counterparts, and these reveal in a way more
suited to the data the important sources of variation in
lip motion. Finally, it is found that the analyses of
acceleration were especially helpful in suggesting
possible control mechanisms. The focus is on using these
speech production data to understand the basic
principles of coordination. However, it is believed that
the tools will have a more general use.
Laboissiere R, Ostry DJ, Feldman AG (1996) The control of
multi-muscle systems: human jaw and hyoid movements. Biol
Cybern 74:373-384.
Abstract
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PDF
A model is
presented of sagittal plane jaw and hyoid motion based
on the lambda model of motor control. The model which is
implemented as a computer simulation includes central
neural control signals, position and velocity dependent
reflexes, reflex delays, and muscle properties such as
the dependence of force on muscle length and velocity.
The model has seven muscles (or muscle groups) attached
to the jaw and hyoid as well as separate jaw and hyoid
bone dynamics. According to the model, movements result
from changes in neurophysiological control variables
which shift the equilibrium state of the motor system.
One such control variable is an independent change in
the membrane potential of alpha-motoneurones (MNs); this
variable establishes a threshold muscle length (lambda)
at which MN recruitment begins. Motor functions may be
specified by various combinations of lambdas. One
combination of lambdas is associated with the level of
coactivation of muscles. Others are associated with
motions in specific degrees of freedom. Using the model,
we study the mapping between control variables specified
at the level of degrees of freedom and control variables
corresponding to individual muscles. We demonstrate that
commands can be defined involving linear combinations of
lambda change which produce essentially independent
movements in each of the four kinematic degrees of
freedom represented in the model (jaw orientation, jaw
position, vertical and horizontal hyoid position). These
linear combinations are represented by vectors in lambda
space which may be scaled in magnitude. The vector
directions are constant over the jaw / hyoid workspace
and result in essentially the same motion from any
workspace position. The demonstration that it is not
necessary to adjust control signals to produce the same
movements in different parts of the workspace supports
the idea that the nervous system need not take explicit
account of musculo-skeletal geometry in planning
movements.
Ostry DJ, Gribble PL, Gracco VL (1996) Coarticulation of jaw
movements in speech production: is context sensitivity in
speech kinematics centrally planned? J Neurosci
16:1570-1579.
Abstract
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PDF
Coarticulation
in speech production is a phenomenon in which the
articulator movements for a given speech sound vary
systematically with the surrounding sounds and their
associated movements. Although these variations may
appear to be centrally planned, without explicit models
of the speech articulators, the kinematic patterns which
are attributable to central control cannot be
distinguished from those which arise due to dynamics and
are not represented in the underlying control signals.
In the present paper, we address the origins of
coarticulation by comparing the results of empirical and
modeling studies of jaw motion in speech. The simulated
kinematics of sagittal plane jaw rotation and horizontal
jaw translation are compared to the results of empirical
studies in which subjects produce speech-like sequences
at a normal rate and volume. The simulations examine
both "anticipatory" and "carryover" coarticulatory
effects. In both cases, the results show that even when
no account is taken of context at the level of central
control, kinematic patterns vary in amplitude and
duration as a function of the magnitude of the preceding
or following movement in the same manner as one observes
empirically in coarticulation. Since at least some
coarticulatory effects may arise from muscle mechanics
and dynamics and not from central control, these factors
must be considered before drawing inferences about
control in coarticulation.
Bonda E, Petrides M, Ostry DJ, Evans A (1996) Specific
involvement of human parietal systems and the amygdala in
the perception of biological motion. J Neurosci
16:3737-3744.
Abstract
|
PDF
To explore the
extent to which functional systems within the human
posterior parietal cortex and the superior temporal
sulcus are involved in the perception of action, we
measured cerebral metabolic activity in human subjects
by positron emission tomography during the perception of
simulations of biological motion with point-light
displays. The experimental design involved comparisons
of activity during the perception of goal-directed hand
action, whole body motion, object motion, and random
motion. The results demonstrated that the perception of
scripts of goal-directed hand action implicates the
cortex in the intraparietal sulcus and the caudal part
of the superior temporal sulcus, both in the left
hemisphere. By contrast, the rostrocaudal part of the
right superior temporal sulcus and adjacent temporal
cortex, and limbic structures such as the amygdala, are
involved in the perception of signs conveyed by
expressive body movements.
Perrier P, Ostry DJ, Laboissiere R (1996) The equilibrium
point hypothesis and its application to speech motor
control. J Speech Hear Res 39:365-377.
Abstract
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PDF
In this paper,
we address a number of issues in speech research in the
context of the equilibrium point hypothesis of motor
control. The hypothesis suggests that movements arise
from shifts in the equilibrium position of the limb or
the speech articulator. The equilibrium is a consequence
of the interaction of central neural commands, reflex
mechanisms, muscle properties and external loads, but it
is under the control of central neural commands. These
commands act to shift the equilibrium via centrally
specified signals acting at the level of the motoneurone
(MN) pool. In the context of a model of sagittal plane
jaw and hyoid motion based on the lambda version of the
equilibrium point hypothesis, we consider the
implications of this hypothesis for the notion of
articulatory targets. We suggest that simple linear
control signals may underlie smooth articulatory
trajectories. We explore as well the phenomenon of
intra-articulator coarticulation in jaw movement. We
suggest that even when no account is taken of upcoming
context, that apparent anticipatory changes in movement
amplitude and duration may arise due to dynamics. We
also present a number of simulations that show in
different ways how variability in measured kinematics
can arise in spite of constant magnitude speech control
signals.
Sergio LE, Ostry DJ (1995) Coordination of multiple muscles
in two degree of freedom elbow movements. Exp Brain Res
105:123-137.
Abstract
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PDF
The present
study quantifies electromyographic (EMG) magnitude,
timing, and duration in one and two degree of freedom
elbow movements involving combinations of flexion /
extension and pronation / supination. The aim is to
understand the organization of commands subserving
motion in individual and multiple degrees of freedom.
The muscles tested in this study fell into two
categories with respect to agonist burst magnitude those
whose burst magnitude varied with motion in a second
degree of freedom at the elbow, and those whose burst
magnitude depended on motion in one degree of freedom
only. In multiarticular muscles contributing to motion
in two degrees of freedom at the elbow, we found that
the magnitude of the agonist burst was greatest for
movements in which a muscle acted as agonist in both
degrees of freedom. The burst magnitudes for one degree
of freedom movements were, in turn, greater than for
movements in which the muscle was agonist in one degree
of freedom and antagonist in the other. It was also
found that for movements in which a muscle acted as
agonist in two degrees of freedom, the burst magnitude
was, in the majority of cases, not different than the
sum of the burst magnitudes in the component movements.
When differences occured, the burst magnitude for the
combined movement was greater than the sum of the
components. Other measures of EMG activity such as burst
onset time and duration were not found to vary in a
systematic manner with motion in these two degrees of
freedom. It was also seen that several muscles which
produced motion in one degree of freedom at the elbow,
including triceps brachii (long head), triceps brachii
(lateral head), and pronator quadratus displayed first
agonist bursts whose magnitude did not vary with motion
in a second degree of freedom. However, for the
monoarticular elbow flexors brachialis and
brachioradialis, agonist burst magnitude was affected by
pronation or supination. Lastly, it was observed that
during elbow movements in which muscles acted as agonist
in one degree of freedom and antagonist in the other,
the muscle activity often displayed both agonist and
antagonist components in the same movement. It was found
that, for pronator teres and biceps brachii, the timing
of the bursts was such that there was activity in these
muscles concurrent with activity in both pure agonists
and pure antagonists. The empirical summation of EMG
burst magnitudes and the presence in a single muscle of
both agonist and antagonist bursts within a movement
suggest that central commands associated with motion in
individual degrees of freedom at the elbow may be
superimposed to produce two degree of freedom elbow
movements.
Bateson EV, Ostry DJ (1995) An analysis of the
dimensionality of jaw movement in speech. J Phon 23:101-117.
Abstract
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PDF
The human jaw
moves in three spatial dimensions, and its motion is
filly specified by three orientation angles and three
positions. Using OPTOTRAK, we characterize the basic
motions in these six degrees of freedom and their
interrelations during speech. As has been reported
previously, the principle components of jaw motion fall
primarily within the midsagittal plane, where the jaw
rotates downward and translates forward during opening
movements and follows a similar path during closing. In
general, the relation between sagittal plane rotation
and horizontal translation (protrusion) is linear.
However, speakers display phoneme-specific differences
in the slope of this relation and its position within
the rotation-translation space. Furthermore, instances
of pure rotation and pure translation are observed.
These findings provide direct support for the claim that
jaw rotation and translation are independently
controlled (Flanagan, Ostry & Feldman, 1990).
Rotations out of the midsagittal plane are also
observed. Yaw about the longitudinal body axis is
approximately three degrees and roll usually less than
two degrees. The remaining non-sagittal component,
lateral translation, is small in magnitude and
uncorrelated with other motions.
Ostry DJ, Munhall KG (1994) Control of jaw orientation and
position in mastication and speech. J Neurophysiol
71:1528-1545.
Abstract
|
PDF
1. The
kinematics of sagittal-plane jaw motion were assessed in
mastication and speech. The movement paths were
described in joint coordinates, in terms of the
component rotations and translations. The analysis
focused on the relationship between rotation and
horizontal translation. Evidence was presented that
these can be separately controlled.
2. In speech, jaw movements were studied during
consonant-vowel utterances produced at different rates
and volumes. In mastication, bolus placement, compliance
and size as well as chewing rate were manipulated. Jaw
movements were recorded using the University of
Wisconsin X-ray microbeam system. Jaw rotation and
translation were calculated on the basis of the motion
of X-ray tracking pellets on the jaw.
3. The average magnitudes of jaw rotation and
translation were greater in mastication than in speech.
In addition, in speech, it was shown that the average
rotation magnitude may vary independent of the
horizontal translation magnitude. In mastication, the
average magnitude of vertical jaw translation was not
dependent on the magnitudes of jaw rotation or horizonal
jaw translation.
4. The magnitude of rotation and horizontal jaw
translation tended to be correlated when examined on a
trial by trial basis. Some subjects also showed a
correlation between jaw rotation and vertical jaw
translation. However, the proportion of variance
accounted for was greater for all subjects in the case
of rotation and horizontal translation.
5. Joint space paths in both mastication and speech were
found to be straight. The pattern was observed at normal
and fast rates of speech and mastication and for loud
speech as well. Straight line paths were also observed
when subjects produced utterances that had both the
syllabic structure and the intonation pattern of speech.
The findings suggest that control may be organized in
terms of an equilibrium jaw orientation and an
equilibrium jaw position.
6. Departures from linearity were also observed. These
were typically associated with differences during jaw
closing in the end time of rotation and translation.
Asynchronies were not observed at the start of jaw
closing in either mastication or speech and the movement
paths were typically linear within this region.
Sergio LE, Ostry DJ (1994) Coordination of mono- and bi-
articular muscles in multi-degree of freedom elbow
movements. Exp Brain Res 97:551-555.
Abstract
| PDF
We investigated
the coordination of mono- and bi-articular muscles
during movements involving one or more degrees of
freedom at the elbow. Subjects performed elbow flexion
(or extension) alone, forearm pronation (or supination)
alone, and combinations of the two. In bi-articular
muscles such as biceps and pronator teres, the amplitude
of agonist EMG activity was dependent on motion in both
degrees of freedom. Agonist burst amplitudes for
combined movements were approximately the sum of the
agonist burst amplitudes for movements in the individual
degrees of freedom. Activity levels in individual
degrees of freedom were, in turn, greater than activity
levels observed when a muscle acted as agonist in one
degree of freedom and antagonist in the other. Other
muscles such as triceps, brachialis, and pronator
quadratus, acted primarily during motion in a single
degree of freedom. The relative magnitude and the timing
of activity between sets of muscles also changed with
motion in a second degree of freedom. These patterns are
comparable to those reported previously in isometric
studies.
Parush A, Ostry DJ (1993) Lower pharyngeal wall
coarticulation in VCV syllables. J Acoust Soc Am 94:715-22.
Abstract
|
PDF
The vocal
tract's motion during speech is a complex patterning of
the movement of many different articulators according to
many different time functions. Understanding this myriad
of gestures is important to a number of different
disciplines including automatic speech recognition,
speech and language pathologies, speech motor control,
and experimental phonetics. Central issues are the
accurate description of the shape of the vocal tract and
determining how each articulator contributes to this
shape. A problem facing all of these research areas is
how to cope with the multivariate data from speech
production experiments. In this paper techniques are
described that provide useful tools for describing
multivariate functional data such as the measurement of
speech movements. The choice of data analysis procedures
has been motivated by the need to partition the
articulator movement in various ways: end effects
separated from shape effects, partitioning of syllable
effects, and the splitting of variation within an
articulator site from variation from between sites. The
techniques of functional data analysis seem admirably
suited to the analyses of phenomena such as these.
Familiar multivariate procedures such as analysis of
variance and principal components analysis have their
functional counterparts, and these reveal in a way more
suited to the data the important sources of variation in
lip motion. Finally, it is found that the analyses of
acceleration were especially helpful in suggesting
possible control mechanisms. The focus is on using these
speech production data to understand the basic
principles of coordination. However, it is believed that
the tools will have a more general use.
Sergio LE, Ostry DJ (1993) Three-dimensional kinematic
analysis of frog hindlimb movement in reflex wiping. Exp
Brain Res 94:53-64.
Abstract
|
PDF
The
three-dimensional kinematics of the hindlimb back-wipe
were examined in spinal frogs. The component movements
were identified and the relationship between stimulus
position and hindlimb configuration was assessed. The
planes of motion of the hindlimb were examined
throughout the movement. The back-wipe comprises three
essential phases: a placing phase (I), in which the foot
is drawn over the back of the frog and placed in a
position near to the stimulus; a pre-whisk phase (II),
in which the endpoint of the foot moves away from the
stimulus; and a whisk/extension phase (III), in which
the stimulus is removed. The pre-whisk phase contributes
to force production for the whisk/extension (III). In
the placing phase a systematic relationship was found
between limb endpoint position and stimulus position in
the rostro-caudal direction. The hip, knee and
metatarsal joint angles were related to the position of
the endpoint in the rostro-caudal direction. However,
different frogs tended to adopt different strategies to
remove the stimulus. In one strategy, when the knee
angle was strongly related to the rostro-caudal stimulus
position, the metatarsal angle was weakly related and
vice versa. Other strategies were observed as well.
There was no adjustment in limb endpoint position for
stimulus placement in the medial-lateral direction.
Consistent with this finding, the point on the foot at
which stimulus contact occurred changed systematically
as a function of medial-lateral stimulus placement.
Thus, in order to remove the stimulus in different
medial-lateral positions, the frog used a different part
of the foot rather than moving the foot in the direction
of the stimulus. In two frogs a relationship was
observed between the elevation of the femur and the
medial-lateral stimulus position. The motion planes of
the hindlimb were studied by examining the instantaneous
plane of motion of the endpoint and the planes of motion
of adjacent limb segments. The motion of the endpoint
was found not to be planar in any phase of the wipe. In
contrast, planar motion of the femur and tibia was
observed for all phases. Systematic changes in the
orientation of these planes characterized the different
phases. The position of the hindlimb was found to be
variable prior to the placing phase. This variability
was not related to stimulus position. However, in trials
with multiple wipes, once an initial limb configuration
was assumed, the limb returned to this configuration
before each wipe in the sequence. Evidence for motor
equivalence was sought in two ways.
Ostry DJ, Feldman AG, Flanagan JR (1991) Kinematics and
control of frog hindlimb movements. J Neurophysiol
65:547-562.
Abstract
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PDF
The determinants
of the motion path of the hindlimb were explored in both
intact and spinal frogs. In the spinal preparations the
kinematic properties of withdrawal and crossed-extension
reflexes were studied. In the intact frog the kinematics
of withdrawal and swimming movements were examined. Frog
hindlimb paths were described in joint angle (intrinsic)
coordinates rather than limb endpoint (extrinsic)
coordinates. 2. To study withdrawal and
crossed-extension reflexes, the initial angles at the
hip, knee, and ankle were varied. Withdrawal and crossed
extension were recorded in three dimension (3-D) with
the use of an infra-red spatial imaging system. Swimming
movements against currents of different speeds were
obtained with high-speed film. 3. Three strategies were
considered related to the form of the hypothesized
equilibrium paths specified by the nervous system: all
trajectories lie on a single line in angular
coordinates; all trajectories are directed toward a
common final position; and all trajectories have the
same direction independent of initial joint
configuration. 4. Joint space paths in withdrawal were
found to be straight and parallel independent of the
initial joint configuration. The hip and knee were found
to start simultaneously and in 75% of the conditions
tested to reach maximum velocity simultaneously.
Hip-knee maximum velocity ratios were similar in
magnitude over differences in initial joint angles. This
is consistent with the observation of parallel paths and
supports the view that the nervous system specifies a
single direction for equilibrium trajectories. 5.
Straight line paths with slopes similar to those
observed in withdrawal in the spinal preparation were
found in swimming movements in the intact frog. Straight
line paths in joint space are consistent with the idea
that swimming and withdrawal are organized and
controlled in a joint-level coordinate system. The
similarities observed between spinal and intact
preparations suggest that a common set of constructive
elements underlies these behaviors. 6. Path curvature
was introduced when joint limits were approached toward
the end of the movement. Depending on the initial joint
angles, the joint movements ended at different times.
When initial joint angles were unequal, joints moving
from smaller initial angles reached their functional
limits earlier and stopped first. 7. In withdrawal and
crossed extension in the spinal frog, velocity profiles
at a given joint were similar over the initial portion
of the curve for movements of different amplitude. This
is consistent with the idea that withdrawal and
crossed-extension movements of different amplitude are
produced by a constant rate of shift of the equilibrium
position.
Ostry DJ, Flanagan JR (1989) Human jaw movement in
mastication and speech. Arch Oral Biol 34:685-693.
Abstract
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PDF
The study of jaw
movement in humans is a primary source of information
about the relationship between voluntary movement and
more primitive motor functions. This study focused on
the geometric form of the velocity function, as measured
by linear voltage displacement transducer. Movement
amplitudes, maximum velocities and durations were
greater in mastication than in speech. Nevertheless,
there were detailed similarities in the shape of the
normalized velocity functions. In jaw-closing movements,
the normalized functions were similar in form over
differences in rate, movement amplitude (speech
movements) and the compliance of the bolus
(mastication). In opening movements, the functions for
mastication and speech were again similar over
differences in amplitude and compliance. However, they
differed in shape for fast and slow movements.
Normalized acceleration and deceleration durations were
approximately equal in rapid movements, whereas, for
slower movements, deceleration took substantially
Ostry DJ, Cooke JD, Munhall KG (1987) Velocity curves of
human arm and speech movements. Exp Brain Res 68:37-46.
Abstract
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PDF
The velocity
curves of human arm and speech movements were examined
as a function of amplitude and rate in both continuous
and discrete movement tasks. Evidence for invariance
under scalar transformation was assessed and a
quantitative measure of the form of the curve was used
to provide information on the implicit cost function in
the production of voluntary movement. Arm, tongue and
jaw movements were studied separately. The velocity
curves of tongue and jaw movement were found to differ
in form as a function of movement duration but were
similar for movements of different amplitude. In
contrast, the velocity curves for elbow movements were
similar in form over differences in both amplitude and
duration. Thus, the curves of arm movement, but not
those of tongue or jaw movement, were geometrically
equivalent in form. Measurements of the ratio of maximum
to average velocity in arm movement were compared with
the theoretical values calculated for a number of
criterion functions. For continuous movements, the data
corresponded best to values computed for the minimum
energy criterion; for discrete movement, values were in
the range of those predicted for the minimum jerk and
best stiffness criteria. The source of a rate dependent
asymmetry in the form of the velocity curve of speech
movements was assessed in a control study in which
subjects produced simple raising and lowering movements
of the jaw without talking. The velocity curves of the
non-speech control gesture were similar in form to those
of jaw movement in speech. These data, in combination
with similar findings for human jaw movement in
mastication, suggest that the asymmetry is not a direct
consequence of the requirements of the task. The
biomechanics and neural control of the orofacial system
may be possible sources of this effect.
Parush A, Ostry DJ (1986) Superior lateral pharyngeal wall
movements in speech. J Acoust Soc Am 80:749-756.
Abstract
|
PDF
Medial movements
of the lateral pharyngeal wall at the level of the
velopharyngeal port were examined by using a
computerized ultrasound system. Subjects produced CVNVC
sequences involving all combinations of the vowels /a/
and /u/ and the nasal consonants /n/ and /m/. The
effects of both vowels on the CVN and NVC gestures
(opening and closing of the velopharyngeal port,
respectively) were assessed in terms of movement
amplitude, duration, and movement onset time. The
amplitude of both opening and closing gestures of the
lateral pharyngeal wall was less in the context of the
vowel /u/ than the vowel /a/. In addition, the onset of
the opening gesture towards the nasal consonant was
related to the identity of both the initial and the
final vowels. The characteristics of the functional
coupling of the velum and lateral pharyngeal wall in
speech are discussed.
Munhall KG, Ostry DJ, Parush A (1985) Characteristics of
velocity profiles of speech movements. J Exp Psychol Hum
Percept Perform 11:457-474.
Abstract
| PDF
The control of
individual speech gestures was investigated by examining
laryngeal and tongue movements during vowel and
consonant production. A number of linguistic
manipulations known to alter the durational
characteristics of speech (i.e., speech rate, lexical
stress, and phonemic identity) were tested. In all cases
a consistent pattern was observed in the kinematics of
the laryngeal and tongue gestures. The ratio of maximum
instantaneous velocity to movement amplitude, a
kinematic index of mass-normalized stiffness, was found
to increase systematically as movement duration
decreased. Specifically, the ratio of maximum velocity
to movement amplitude varied as a function of a
parameter, C, times the reciprocal of movement duration.
The conformity of the data to this relation indicates
that durational change is accomplished by scalar
adjustment of a base velocity form. These findings are
consistent with the idea that kinematic change is
produced by the specification of articulator stiffness.
Ostry DJ, Munhall KG (1985) Control of rate and duration of
speech movements. J Acoust Soc Am 77:640-648.
Abstract
|
PDF
A computerized
pulsed-ultrasound system was used to monitor tongue
dorsum movements during the production of
consonant-vowel sequences in which speech rate, vowel,
and consonant were varied. The kinematics of tongue
movement were analyzed by measuring the lowering gesture
of the tongue to give estimates of movement amplitude,
duration, and maximum velocity. All three subjects in
the study showed reliable correlations between the
amplitude of the tongue dorsum movement and its maximum
velocity. Further, the ratio of the maximum velocity to
the extent of the gesture, a kinematic indicator of
articulator stiffness, was found to vary inversely with
the duration of the movement. This relationship held
both within individual conditions and across all
conditions in the study such that a single function was
able to accommodate a large proportion of the variance
due to changes in movement duration. As similar findings
have been obtained both for abduction and adduction
gestures of the vocal folds and for rapid voluntary limb
movements, the data suggest that a wide range of changes
in the duration of individual movements might all have a
similar origin. The control of movement rate and
duration through the specification of biomechanical
characteristics of speech articulators is discussed.
Parush A, Ostry DJ, Munhall KG (1983) A kinematic study of
lingual coarticulation in VCV sequences. J Acoust Soc Am
74:1115-1125.
Abstract
|
PDF
Intra-articulator anticipatory and carryover
coarticulation were assessed in both temporal and
spatial terms. Three subjects produced VCV sequences
with velar stop consonants and back vowels. Pulsed
ultrasound was used to examine the vertical
displacement, duration, and maximum velocity of the
tongue dorsum raising (VC transition) and lowering (CV
transition) gestures. Anticipatory coarticulation was
primarily temporal for two subjects, with decreases in
the duration of the VC transition accompanying increases
in displacement for the CV transition. Carryover
coarticulation was primarily spatial for all three
subjects, with decreases in CV displacement and maximum
velocity accompanying increases in VC displacement. It
is suggested that these intra-articulator patterns can
be accounted for in terms of an interaction between the
raising gesture and a vowel-specific onset time of the
lowering gesture towards the vowel. The implications of
this kinematic characterization are discussed.
Ostry DJ, Keller E, Parush A (1983) Similarities in the
control of the speech articulators and the limbs: kinematics
of tongue dorsum movement in speech. J Exp Psychol Hum
Percept Perform 9:622-636.
Abstract
|
PDF
The kinematics
of tongue dorsum movements in speech were studied with
pulsed ultrasound to assess similarities in the
voluntary control of the speech articulators and the
limbs. The stimuli were consonant--vowel syllables in
which speech rate and stress were varied. The kinematic
patterns for tongue dorsum movements were comparable to
those observed in the rapid movement of the arms and
hands. The maximum velocity of tongue dorsum raising and
lowering was correlated with the extent of the gesture.
The slope of the relationship differed for stressed and
unstressed vowels but was unaffected by differences in
speech rate. At each stress level the correlation
between displacement and peak velocity was accompanied
by a relatively constant interval from the initiation of
the movement to the point of maximum velocity. The data
are discussed with reference to systems that can be
described with second-order differential equations. The
increase in the slope of the displacement/peak-velocity
relationship for unstressed versus stressed vowels is
suggestive of a tonic increase in articulator stiffness.
Variations in displacement are attributed to the level
of phasic activity in the muscles producing the gesture.
Keller E, Ostry DJ (1983) Computerized measurement of tongue
dorsum movements with pulsed-echo ultrasound. J Acoust Soc
Am 73:1309-1315.
Abstract
|
PDF
A computerized
system for the measurement of tongue dorsum movements
with pulsed echo ultrasound is described. The
presentation focuses on technical and methodological
considerations in the on-line acquisition of vertical
tongue movement information, its digital processing and
display. Problems associated with transducer placement,
peak detection, data averaging, and curve fitting are
considered, and validation procedures based on x ray and
indicators of measurement reliability are reported. The
discussion centers on advantages and disadvantages of
the technique and its applications.
Ostry DJ (1983) Determinants of interkey times in typing. In
W. E. Cooper (ed.), Cognitive Aspects of Skilled
Typewriting, Springer-Verlag New York Inc.
Abstract
|
PDF
Typewriting,
musical instrument playing, spoken language, and dance
involve sophisticated motor skills and associated symbol
schemes. Researchers in cognition have been interested
in these abilities because they enable the study of
relations between the structure of motor behavior and
the organization of the associated formal system.
Typewriting, in particular, is of interest because of
the remarkable rate and complexity of finger and hand
movements involved and because its performance is
readily quantifiable. However, if typewriting is to be
used to study either cognitive or motor organization,
the factors contributing to its temporal structure must
be identified. In this chapter I present the findings of
several studies that examine variables that influence
the pattern of interkey times in typing. In addition to
providing evidence on the constituents of control in
typing, the studies provide a basis for the examination
of proposals by Ostry (1980) and Sternberg, Monsell,
Knoll, and Wright (1978) that certain aspects of typing
control are inherently tied to the execution of the
sequence. The suggestions arise from observations that
patterns of initial latency and interkey time are not
changed by the introduction of a delay between stimulus
presentation and a response signal. The inability to
take advantage of a preparation interval seems to
indicate that the programming of typing movements is
intimately linked to their execution.