Sing GF, Orozco SP & Smith MA (2013). Limb motion dictates how motor learning arises from arbitrary environmental dynamics.
Journal of Neurophysiology, 109: 2466-2482, January 30, 2013.
Abstract:
A key idea in motor learning is that
internal models of environmental dynamics are internally represented
as functions of spatial variables including position, velocity, and
acceleration of body motion. We refer to such a representation as
motion dependent. The evidence for a motion-dependent representation
is, however, primarily based on examination of the adaptation to
motion-dependent dynamic environments. To more rigorously test
this idea, we examined the adaptive response to perturbations that
cannot be well approximated by motion-state: force-impulses— brief,
high-amplitude pulses of force. The induced adaptation characterizes
the impulse response of the system—a widely used technique for
probing system dynamics in engineering systems identification. Here
we examined the adaptive responses to two different force-impulse
perturbations during human voluntary reaching movements. We found
that although neither could be well approximated by motion-state
(R2 < 0.18 in both cases), both perturbations induced single-trial
adaptive responses that were (R2 > 0.87). Moreover, these responses
were similar in shape to those induced by low-fidelity motion-based
approximations of the force-impulses (r > 0.88). Remarkably, we
found that the motion dependence of the adaptive responses to
force-impulses persisted, even after prolonged exposure (R2 > 0.95).
During a 300-trial training period, trial-to-trial fluctuations in the
position, velocity, and acceleration of motion accurately predicted
trial-to-trial fluctuations in the adaptive response, and the adaptation
gradually became more specific to the perturbation, but only via
reorganization of the structure of the motion-dependent representation.
These results indicate that internal models of environmental
dynamics represent these dynamics in a motion-dependent manner,
regardless of the nature of the dynamics encountered.
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