A temporal predictive code for voice motor control: Evidence from ERP and behavioral responses to pitch-shifted auditory feedback

Abstract

The predictive coding model suggests that voice motor control is regulated by a process in which the mismatch (error) between feedforward predictions and sensory feedback is detected and used to correct vocal motor behavior. In this study, we investigated how predictions about timing of pitch perturbations in voice auditory feedback would modulate ERP and behavioral responses during vocal production. We designed six counterbalanced blocks in which a +100 cents pitch-shift stimulus perturbed voice auditory feedback during vowel sound vocalizations. In three blocks, there was a fixed delay (500, 750 or 1000 ms) between voice and pitch-shift stimulus onset (predictable), whereas in the other three blocks, stimulus onset delay was randomized between 500, 750 and 1000 ms (unpredictable). We found that subjects produced compensatory (opposing) vocal responses that started at 80 ms after the onset of the unpredictable stimuli. However, for predictable stimuli, subjects initiated vocal responses at 20 ms before and followed the direction of pitch shifts in voice feedback. Analysis of ERPs showed that the amplitudes of the N1 and P2 components were significantly reduced in response to predictable compared with unpredictable stimuli. These findings indicate that predictions about temporal features of sensory feedback can modulate vocal motor behavior. In the context of the predictive coding model, temporally-predictable stimuli are learned and reinforced by the internal feedforward system, and as indexed by the ERP suppression, the sensory feedback contribution is reduced for their processing. These findings provide new insights into the neural mechanisms of vocal production and motor control.

Keywords: Auditory feedback; Event-related potential; Internal forward model; Pitch-shift stimulus; Predictive code; Voice motor control.

Figure 1

Experimental design for measuring behavioral and neurophysiological responses to predictable and unpredictable pitch shift onsets in voice auditory feedback. Subjects repeatedly produced a steady vocalization of the vowel sound /a/ while a brief (200 ms) upward pitch shift stimulus at +100 cents perturbed voice auditory feedback in the middle of each vocalization trial. a) In three blocks, there was a fixed delay of 500, 750 or 1000 ms between voice and pitch shift stimulus onset (predictable timing), and b) in the remaining three blocks, the time delay between voice and stimulus onset was randomized between 500, 750 or 1000 ms (unpredictable timing). The order of all six vocalization blocks was counterbalanced across subjects and approximately a total of 900 vocalizations were recorded for each individual subject.

Figure 2

a) Grand-average behavioral vocal responses to pitch shift stimuli overlaid across predictable and unpredictable stimulus onset for three different stimulus onsets at 500 ms, 750 ms and 1000 ms. b) Bar plot representation of the results of analysis on the onset latency and c) the peak magnitude of vocal responses to predictable and unpredictable pitch shift stimuli onset at 500, 750 and 1000 ms latencies.

Figure 3

The overlaid grand-average ERP responses for predictable and unpredictable pitch shift stimulus onset at Fz, FCz and Cz electrodes plotted for each stimulus onset time, separately.

Figure 4

The grand-average ERP responses overlaid across all three stimulus onset times (500, 750 and 1000 ms) plotted separately for predictable and unpredictable pitch shift stimulus onsets at Fz, FCz and Cz electrodes.

Figure 5

The bar plots summarizing the results of analysis for a) the N1 and b) the P2 ERP amplitudes in response to predictable vs. unpredictable pitch-shift stimulus onsets at frontal, frontocentral, central, centroparietal, parietal, parietooccipital, and the left and right temporal electrode sites.

Figures 6

The topographical distribution maps of the scalp-recorded potentials in response to predictable and unpredictable pitch-shift stimulus onsets for a) the N1 and b) the P2 ERP components.