Abstract |
PDF
This
study tests for a function of the somatosensory cortex,
that, in addition to its role in processing somatic
afferent information, somatosensory cortex contributes
both to motor learning and the stabilization of motor
memory. Continuous theta-burst magnetic stimulation
(cTBS) was applied, before force-field training to
disrupt activity in either the primary somatosensory
cortex, primary motor cortex, or a control zone over the
occipital lobe. Tests for retention and relearning were
conducted after a 24 h delay. Analysis of movement
kinematic measures and force-channel trials found that
cTBS to somatosensory cortex disrupted both learning and
subsequent retention, whereas cTBS to motor cortex had
little effect on learning but possibly impaired
retention. Basic movement variables are unaffected by
cTBS suggesting that the stimulation does not interfere
with movement but instead disrupts changes in the cortex
that are necessary for learning. In all experimental
conditions, relearning in an abruptly introduced force
field, which followed retention testing, showed
extensive savings, which is consistent with previous
work suggesting that more cognitive aspects of learning
and retention are not dependent on either of the
cortical zones under test. Taken together, the findings
are consistent with the idea that motor learning is
dependent on learning-related activity in the
somatosensory cortex. NEW & NOTEWORTHY This study
uses noninvasive transcranial magnetic stimulation to
test the contribution of somatosensory and motor cortex
to human motor learning and retention. Continuous
theta-burst stimulation is applied before learning;
participants return 24 h later to assess retention.
Disruption of the somatosensory cortex is found to
impair both learning and retention, whereas disruption
of the motor cortex has no effect on learning. The
findings are consistent with the idea that motor
learning is dependent upon learning-related plasticity
in somatosensory cortex.
Franken M, Liu B, Ostry DJ (2022) Towards a
somatosensory theory of speech perception. J
Neurophysiol 128: 1683-1695.
Abstract
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.