Opposing and following vocal responses to pitch-shifted auditory feedback: evidence for different mechanisms of voice pitch control.

The present study describes a technique for analysis of vocal responses to auditory feedback pitch perturbations in which individual trials are first sorted according to response direction and then separately averaged in groups of upward or downward responses. In experiment 1, the stimulus direction was predictable (all upward) but magnitude was randomized between +100, +200, or +500 cents (unpredictable). Results showed that pitch-shift stimuli (PSS) of +100 and +200 cents elicited significantly larger opposing (compensatory) responses than +500 cent stimuli, but no such effect was observed for "following" responses. In experiment 2, subjects were tested in three blocks of trials where for the first two, PSS magnitude and direction were predictable (block 1+100 and block 2-100 cents), and in block 3, the magnitude was predictable (±100 cents) but direction was randomized (upward or downward). Results showed there were slightly more opposing than following responses for predictable PSS direction, but randomized directions led to significantly more opposing than following responses. Results suggest that predictability of stimulus direction and magnitude can modulate vocal responses to feedback pitch perturbations. The function and causes of the opposing and following responses are unknown, but there may be two different neural mechanisms involved in their production.