Publications
Ebrahimi
S, Ostry DJ (2023)
The
human somatosensory cortex contributes to the encoding of
newly learned movements. PNAS
Darainy M, Manning TF (2023) Disruption
of somatosensory cortex impairs motor learning and
retention. J Neurophysiol
Franken
M, Liu B, Ostry DJ (2022) Towards a somatosensory theory
of speech perception. J Neurophysiol 128: 1683-1695.
Abstract
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°
or 30°). 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°
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.
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.
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.
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.
Darainy M,
Vahdat S, Ostry DJ (2019) Neural basis of sensorimotor
learning in speech motor adaptation. Cereb Cortex
29:2876-2889.
Abstract
PDF
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
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
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.
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)
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 which 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.
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.
When we speak, we
get correlated sensory feedback from speech sounds and
from the muscles and soft tissues of the vocal tract.
Here we dissociate the contributions of auditory and
somatosensory feedback to identify brain networks that
underlie the somatic contribution to speech motor
learning. The technique uses a robotic device that
selectively alters somatosensory inputs in combination
with resting-state fMRI scans that reveal
learning-related changes in functional connectivity. A
partial correlation analysis is used to identify
connectivity changes that are not explained by the time
course of activity in any other learning-related areas.
This analysis revealed changes related to behavioral
improvements in movement and separately, to changes in
auditory perception: Speech motor adaptation itself was
associated with connectivity changes that were primarily
in non-motor areas of brain, specifically, to a
strengthening of connectivity between auditory and
somatosensory cortex and between presupplementary motor
area and the inferior parietal lobule. In contrast,
connectively changes associated with alterations to
auditory perception were restricted to speech motor
areas, specifically, primary motor cortex and inferior
frontal gyrus. Overall, our findings show that during
adaptation, somatosensory inputs result in a broad range
of changes in connectivity in areas associated with
speech motor control and learning.
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.
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.
Laboissière 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 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 PDF
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
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, Laboissière R, Ostry DJ
(2002) The relationship between jaw stiffness and
kinematic variability in speech. J Neurophysiol
88:2329-2340.
Abstract
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,
Laboissière R (2001) Compensation for the effects of
head acceleration on jaw movement in speech. J
Neurosci 21:6447-6456.
Abstract
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.
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
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
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 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
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
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,
Laboissière R (1998) Are complex control signals
required for human arm movement? J Neurophysiol
79:1409-1424.
Abstract
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, Laboissière R, Ostry
DJ (1998) A dynamic biomechanical model for neural
control of speech production. J Acoust Soc Am
103:1615-1627.
Abstract
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 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 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
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
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.
Laboissière R, Ostry DJ, Feldman AG
(1996) The control of multi-muscle systems: human
jaw and hyoid movements. Biol Cybern 74:373-384.
Abstract
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 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, Laboissière R
(1996) The equilibrium point hypothesis and its
application to speech motor control. J Speech Hear
Res 39:365-377.
Abstract
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
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
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
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 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
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
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.