SPEECH MOTOR CONTROL - ACOUSTIC GOALS, SATURATION EFFECTS, AUDITORY-FEEDBACK AND INTERNAL MODELS

A theoretical overview and supporting data are presented about the con trol of the segmental component of speech production. Findings of ''mo tor-equivalent'' trading relations between the contributions of two co nstrictions to the same acoustic transfer function provide preliminary support for the idea that segmental control is based on acoustic or a uditory-perceptual goals. The goals an determined partly by non-linear , quantal relations (called ''saturation effects'') between motor comm ands and articulatory movements and between articulation and sound. Si nce processing times would be too long to allow the use of auditory fe edback for closed-loop error correction in achieving acoustic goals, t he control mechanism must use a robust ''internal model'' of the relat ion between articulation and the sound output that is learned during s peech acquisition. Studies of the speech of cochlear implant and bilat eral acoustic neuroma patients provide evidence supporting two roles f or auditory feedback in adults: maintenance of the internal model, and monitoring the acoustic environment to help assure intelligibility by guiding relatively rapid adjustments in ''postural'' parameters under lying average sound level, speaking rate and the amount of prosodicall y-based inflection of FO and SPL. (C) 1997 Elsevier Science B.V.