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Specificity of Speech Motor Learning
David J. Ostry and Stephanie Tremblay

The idea that the brain controls movement on the basis of an internal model of dynamics has been one of the dominant hypotheses in motor control research for over a decade. Speech motor learning offers a unique opportunity to test this hypothesis by providing the possibility of matching utterances in terms of their dynamics. If adaptation involves learning an internal model of articulator dynamics, then learning should transfer to utterances with similar dynamics. In the present study, subjects learned to produce speech movements in an altered dynamic environment in which a robot applied mechanical loads to the jaw in proportion to velocity. Following training subjects were asked to produce a test utterance in order to assess transfer of learning. The training and transfer utterances were matched on a continuum that extended from equating the dynamics of jaw movements alone to a global match across the movements of multiple articulators. In each situation, subjects adapted to the training utterance yet failed to show transfer to an utterance that was matched on dynamics. These results point to the specificity of speech motor learning and argue against the idea that motor control involves a generalized dynamics model.

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