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

Abstract

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.

Figure 1

Graphs depicting voice F0 responses to pitch shift stimuli of +100 cents (A), +200 cents (B), and +500 cents (C). Solid black curves show responses changing in the opposite direction to the stimulus (opposing), dashed black lines show responses changing in the same direction as the stimulus (following), and grey lines show responses that are a combination of opposing and following responses. Vertical bars represent standard error of the mean of the averaged traces.

Figure 2

Graphs depicting voice F0 responses to pitch shift stimuli plotted individually for opposing (A), following (B), and combined (C) opposing plus following responses. Black dashed lines show responses to 100 cent stimuli, solid black lines show responses to 200 cent stimuli, and grey lines show responses to 500 cent stimuli. Horizontal array of asterisks in (B) show time period where responses to 100 and 200 cents stimuli were significantly larger than those to 500 cent stimuli.

Figure 3

Graphs depicting voice F0 responses to pitch shift stimuli in the upward direction (left) and downward direction (right). Top row of plots show responses to stimuli that were randomized in their direction (unpredictable direction). Bottom row of plots show responses to stimuli that were not randomized in their direction (predictable direction). Solid black traces show opposing responses, black dashed traces show following responses, and grey traces show the combination of opposing and following responses. Arrows indicate time of marked change in rate of return of following responses towards baseline discussed in text. Square brackets at bottom show time and direction of stimuli.

Figure 4

Bar plots of mean response magnitude for upward and downward responses for the pre-sorted data. Plots illustrate gradation of response magnitudes by subject and arranged from smallest to largest magnitudes on the x-axis.