Sensorimotor adaptation to feedback perturbations of vowel acoustics and its relation to perception.

The role of auditory feedback in speech motor control was explored in three related experiments. Experiment 1 investigated auditory sensorimotor adaptation: the process by which speakers alter their speech production to compensate for perturbations of auditory feedback. When the first formant frequency (F1) was shifted in the feedback heard by subjects as they produced vowels in consonant-vowel-consonant (CVC) words, the subjects' vowels demonstrated compensatory formant shifts that were maintained when auditory feedback was subsequently masked by noise-evidence of adaptation. Experiment 2 investigated auditory discrimination of synthetic vowel stimuli differing in F1 frequency, using the same subjects. Those with more acute F1 discrimination had compensated more to F1 perturbation. Experiment 3 consisted of simulations with the directions into velocities of articulators model of speech motor planning, which showed that the model can account for key aspects of compensation. In the model, movement goals for vowels are regions in auditory space; perturbation of auditory feedback invokes auditory feedback control mechanisms that correct for the perturbation, which in turn causes updating of feedforward commands to incorporate these corrections. The relation between speaker acuity and amount of compensation to auditory perturbation is mediated by the size of speakers' auditory goal regions, with more acute speakers having smaller goal regions.