By L. Max and L.S. Hine
The central nervous systemís ability to adjust motor commands in response to unanticipated consequences of the resulting movements is critical for adaptive sensorimotor control. Observations of such adaptation and after-effects in the presence of externally manipulated sensory information suggest that subjects are able re-learn the mapping between motor commands and afferent information. Unfortunately, little is known about sensorimotor adaptation and after-effects during speech production. We will report initial results from work investigating articulatory and phonatory adjustments in response to independent manipulations of formant- and fundamental frequency-related auditory feedback. Subjects produced isolated vowels in control (non-manipulated feedback) and experimental (manipulation of either formant frequencies or fundamental frequency) conditions with feedback delivered through insert earphones. Four experimental conditions involved formant manipulations (relatively small and large shifts up and down) and four involved fundamental frequency manipulations (relatively small and large shifts up and down). Automatic software routines were used to extract fundamental frequency, first formant frequency, and second formant frequency (a) averaged across the middle 50% of each vowel, and (b) at time points 25%, 50%, and 75% into each vowel. Results will be presented and implications regarding the integration of auditory feedback and internal models in the sensorimotor control of speech production will be discussed.