Speech motor adaptation during synchronous and metronome-timed speech

Sensorimotor integration during speech has been investigated by altering the sound of a speaker's voice in real time; in response, the speaker learns to change their production of speech sounds in order to compensate (adaptation). This line of research has however been predominantly limited to very simple speaking contexts, typically involving (a) repetitive production of single words and (b) production of speech while alone, without the usual exposure to other voices. This study investigated adaptation to a real-time perturbation of the first and second formants during production of sentences either in synchrony with a prerecorded voice (synchronous speech group) or alone (solo speech group). Experiment 1 (n = 30) found no significant difference in the average magnitude of compensatory formant changes between the groups; however, synchronous speech resulted in increased between-individual variability in such formant changes. Participants also showed acoustic-phonetic convergence to the voice they were synchronizing with prior to introduction of the feedback alteration. Furthermore, the extent to which the changes required for convergence agreed with those required for adaptation was positively correlated with the magnitude of subsequent adaptation. Experiment 2 tested an additional group with a metronome-timed speech task (n = 15) and found a similar pattern of increased between-participant variability in formant changes. These findings demonstrate that speech motor adaptation can be measured robustly at the group level during performance of more complex speaking tasks; however, further work is needed to resolve whether self-voice adaptation and other-voice convergence reflect additive or interactive effects during sensorimotor control of speech.