This work involving both speech and
arm movement finds evidence in support of the idea that
human motor learning is substantially local.
Rochet-Capellan A, Richer L, Ostry DJ (2012)
Non-homogeneous transfer reveals specificity in speech
motor learning, J Neurophysiol 107:1711-1717.
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.
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.
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.
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.