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.
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.
Laboissičre 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
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, Laboissičre 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, Laboissičre 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.
Abstract |
PDF
Suzuki M, Shiller DM, Gribble
PL, Ostry DJ (2001) Relationship between
cocontraction, movement kinematics and phasic
muscle activity in single-joint arm movement.
Exp Brain Res 140:171-181.
Abstract
| PDF
Patterns of muscle
coactivation provide a window into
mechanisms of limb stabilization. In the
present paper we have examined muscle
coactivation in single-joint elbow and
single-joint shoulder movements and
explored its relationship to movement
velocity and amplitude, as well as phasic
muscle activation patterns. Movements were
produced at several speeds and different
amplitudes, and muscle activity and
movement kinematics were recorded. Tonic
levels of electromyographic (EMG) activity
following movement provided a measure of
muscle cocontraction. It was found that
coactivation following movement increased
with maximum joint velocity at each of two
amplitudes. Phasic EMG activity in agonist
and antagonist muscles showed a similar
correlation that was observable even
during the first 30 ms of muscle
activation. All subjects but one showed
statistically significant correlations on
a trial-by-trial basis between tonic and
phasic activity levels, including the
phasic activity measure taken at the
initiation of movement. Our findings
provide direct evidence that muscle
coactivation varies with movement
velocity. The data also suggest that
cocontraction is linked in a simple manner
to phasic muscle activity. The similarity
in the patterns of tonic and phasic
activation suggests that the nervous
system may use a simple strategy to adjust
coactivation and presumably limb impedance
in association with changes in movement
speed. Moreover, since the pattern of
tonic activity varies with the first 30 ms
of phasic activity, the control of
cocontraction may be established prior to
movement onset.
Ostry DJ, Romo R (2001)
Tactile shape processing. Neuron 31:173-174.
Abstract | 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, Laboissičre 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, Laboissičre 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.
Laboissičre 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,
Laboissičre 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 |
PDF
We investigated the
coordination of mono- and bi-articular
muscles during movements involving one or
more degrees of freedom at the elbow.
Subjects performed elbow flexion (or
extension) alone, forearm pronation (or
supination) alone, and combinations of the
two. In bi-articular muscles such as biceps
and pronator teres, the amplitude of agonist
EMG activity was dependent on motion in both
degrees of freedom. Agonist burst amplitudes
for combined movements were approximately
the sum of the agonist burst amplitudes for
movements in the individual degrees of
freedom. Activity levels in individual
degrees of freedom were, in turn, greater
than activity levels observed when a muscle
acted as agonist in one degree of freedom
and antagonist in the other. Other muscles
such as triceps, brachialis, and pronator
quadratus, acted primarily during motion in
a single degree of freedom. The relative
magnitude and the timing of activity between
sets of muscles also changed with motion in
a second degree of freedom. These patterns
are comparable to those reported previously
in isometric studies.
Parush A, Ostry DJ (1993)
Lower pharyngeal wall coarticulation in VCV
syllables. J Acoust Soc Am 94:715-22.
Abstract
| PDF
The vocal tract's motion
during speech is a complex patterning of the
movement of many different articulators
according to many different time functions.
Understanding this myriad of gestures is
important to a number of different
disciplines including automatic speech
recognition, speech and language
pathologies, speech motor control, and
experimental phonetics. Central issues are
the accurate description of the shape of the
vocal tract and determining how each
articulator contributes to this shape. A
problem facing all of these research areas
is how to cope with the multivariate data
from speech production experiments. In this
paper techniques are described that provide
useful tools for describing multivariate
functional data such as the measurement of
speech movements. The choice of data
analysis procedures has been motivated by
the need to partition the articulator
movement in various ways: end effects
separated from shape effects, partitioning
of syllable effects, and the splitting of
variation within an articulator site from
variation from between sites. The techniques
of functional data analysis seem admirably
suited to the analyses of phenomena such as
these. Familiar multivariate procedures such
as analysis of variance and principal
components analysis have their functional
counterparts, and these reveal in a way more
suited to the data the important sources of
variation in lip motion. Finally, it is
found that the analyses of acceleration were
especially helpful in suggesting possible
control mechanisms. The focus is on using
these speech production data to understand
the basic principles of coordination.
However, it is believed that the tools will
have a more general use.
Sergio LE, Ostry DJ (1993)
Three-dimensional kinematic analysis of frog
hindlimb movement in reflex wiping. Exp Brain
Res 94:53-64.
Abstract
| PDF
The three-dimensional
kinematics of the hindlimb back-wipe were
examined in spinal frogs. The component
movements were identified and the
relationship between stimulus position and
hindlimb configuration was assessed. The
planes of motion of the hindlimb were
examined throughout the movement. The
back-wipe comprises three essential phases:
a placing phase (I), in which the foot is
drawn over the back of the frog and placed
in a position near to the stimulus; a
pre-whisk phase (II), in which the endpoint
of the foot moves away from the stimulus;
and a whisk/extension phase (III), in which
the stimulus is removed. The pre-whisk phase
contributes to force production for the
whisk/extension (III). In the placing phase
a systematic relationship was found between
limb endpoint position and stimulus position
in the rostro-caudal direction. The hip,
knee and metatarsal joint angles were
related to the position of the endpoint in
the rostro-caudal direction. However,
different frogs tended to adopt different
strategies to remove the stimulus. In one
strategy, when the knee angle was strongly
related to the rostro-caudal stimulus
position, the metatarsal angle was weakly
related and vice versa. Other strategies
were observed as well. There was no
adjustment in limb endpoint position for
stimulus placement in the medial-lateral
direction. Consistent with this finding, the
point on the foot at which stimulus contact
occurred changed systematically as a
function of medial-lateral stimulus
placement. Thus, in order to remove the
stimulus in different medial-lateral
positions, the frog used a different part of
the foot rather than moving the foot in the
direction of the stimulus. In two frogs a
relationship was observed between the
elevation of the femur and the
medial-lateral stimulus position. The motion
planes of the hindlimb were studied by
examining the instantaneous plane of motion
of the endpoint and the planes of motion of
adjacent limb segments. The motion of the
endpoint was found not to be planar in any
phase of the wipe. In contrast, planar
motion of the femur and tibia was observed
for all phases. Systematic changes in the
orientation of these planes characterized
the different phases. The position of the
hindlimb was found to be variable prior to
the placing phase. This variability was not
related to stimulus position. However, in
trials with multiple wipes, once an initial
limb configuration was assumed, the limb
returned to this configuration before each
wipe in the sequence. Evidence for motor
equivalence was sought in two ways.
Ostry DJ, Feldman AG,
Flanagan JR (1991) Kinematics and control of
frog hindlimb movements. J Neurophysiol
65:547-562.
Abstract
| PDF
The determinants of the
motion path of the hindlimb were explored in
both intact and spinal frogs. In the spinal
preparations the kinematic properties of
withdrawal and crossed-extension reflexes
were studied. In the intact frog the
kinematics of withdrawal and swimming
movements were examined. Frog hindlimb paths
were described in joint angle (intrinsic)
coordinates rather than limb endpoint
(extrinsic) coordinates. 2. To study
withdrawal and crossed-extension reflexes,
the initial angles at the hip, knee, and
ankle were varied. Withdrawal and crossed
extension were recorded in three dimension
(3-D) with the use of an infra-red spatial
imaging system. Swimming movements against
currents of different speeds were obtained
with high-speed film. 3. Three strategies
were considered related to the form of the
hypothesized equilibrium paths specified by
the nervous system: all trajectories lie on
a single line in angular coordinates; all
trajectories are directed toward a common
final position; and all trajectories have
the same direction independent of initial
joint configuration. 4. Joint space paths in
withdrawal were found to be straight and
parallel independent of the initial joint
configuration. The hip and knee were found
to start simultaneously and in 75% of the
conditions tested to reach maximum velocity
simultaneously. Hip-knee maximum velocity
ratios were similar in magnitude over
differences in initial joint angles. This is
consistent with the observation of parallel
paths and supports the view that the nervous
system specifies a single direction for
equilibrium trajectories. 5. Straight line
paths with slopes similar to those observed
in withdrawal in the spinal preparation were
found in swimming movements in the intact
frog. Straight line paths in joint space are
consistent with the idea that swimming and
withdrawal are organized and controlled in a
joint-level coordinate system. The
similarities observed between spinal and
intact preparations suggest that a common
set of constructive elements underlies these
behaviors. 6. Path curvature was introduced
when joint limits were approached toward the
end of the movement. Depending on the
initial joint angles, the joint movements
ended at different times. When initial joint
angles were unequal, joints moving from
smaller initial angles reached their
functional limits earlier and stopped first.
7. In withdrawal and crossed extension in
the spinal frog, velocity profiles at a
given joint were similar over the initial
portion of the curve for movements of
different amplitude. This is consistent with
the idea that withdrawal and
crossed-extension movements of different
amplitude are produced by a constant rate of
shift of the equilibrium position.
Ostry DJ, Flanagan JR (1989)
Human jaw movement in mastication and speech.
Arch Oral Biol 34:685-693.
Abstract
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The study of jaw movement
in humans is a primary source of information
about the relationship between voluntary
movement and more primitive motor functions.
This study focused on the geometric form of
the velocity function, as measured by linear
voltage displacement transducer. Movement
amplitudes, maximum velocities and durations
were greater in mastication than in speech.
Nevertheless, there were detailed
similarities in the shape of the normalized
velocity functions. In jaw-closing
movements, the normalized functions were
similar in form over differences in rate,
movement amplitude (speech movements) and
the compliance of the bolus (mastication).
In opening movements, the functions for
mastication and speech were again similar
over differences in amplitude and
compliance. However, they differed in shape
for fast and slow movements. Normalized
acceleration and deceleration durations were
approximately equal in rapid movements,
whereas, for slower movements, deceleration
took substantially
Ostry DJ, Cooke JD, Munhall
KG (1987) Velocity curves of human arm and
speech movements. Exp Brain Res 68:37-46.
Abstract
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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
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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
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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
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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
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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
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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
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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.