"Compensatory articulation" under conditions of reduced afferent information: a dynamic formulation.

A well-established feature of speech production is that talkers, faced with either anticipated or unanticipated perturbations, can spontaneously adjust the movement patterns of articulators such that the acoustic output remains relatively undistorted. Less clear is the nature of the underlying processes involved. In this study we examined five subjects' productions of the point vowels /i, a, u/ in isolation and of the same vowels embedded in a dynamic speech context under normal conditions and under a combined condition, in which (a) the mandible was fixed by means of a bite block; (b) proprioceptive information was reduced through bilateral anesthetization of the temporomandibular joint; (c) tactile information from the oral mucosa was reduced by application of a topical anesthetic; and (d) auditory information was masked by white noise. Minimal distortion of the formant patterns was found in the combined condition. These findings are unfavorable for central (e.g., predictive simulation) or peripheral closed-loop models, both of which require reliable peripheral information; they are more in line with recent work suggesting that movement goals may be achieved by muscle collectives that behave in a way that is qualitatively similar to a nonlinear vibratory system.