Evidence suggests that temporal predictions arising from the motor system can enhance auditory perception. However, in speech perception, we lack evidence of perception being modulated by production. Here we show a behavioural protocol that captures the existence of such auditory–motor interactions. Participants performed a syllable discrimination task immediately after producing periodic syllable sequences. Two speech rates were explored: a ‘natural’ (individually preferred) and a fixed ‘non-natural’ (2 Hz) rate. Using a decoding approach, we show that perceptual performance is modulated by the stimulus phase determined by a participant’s own motor rhythm. Remarkably, for ‘natural’ and ‘non-natural’ rates, this finding is restricted to a subgroup of the population with quantifiable auditory–motor coupling. The observed pattern is compatible with a neural model assuming a bidirectional interaction of auditory and speech motor cortices. Crucially, the model matches the experimental results only if it incorporates individual differences in the strength of the auditory–motor connection.
Speaking rhythmically can shape hearing
Speech production entrains perception only in high synchronizers. (A) Participants listened with earphones to white noise and continuously whispered the syllable /TE/. After they stopped speech production, a probe syllable (/PO/ or /PU/; blue speech wave in noise) was presented at individual participants speech-in-noise threshold level in varying phases (blue arrows) of the speech production rhythm (indicated by the sinus wave in orange). Participants performed a syllable discrimination task (/PO/ or /PU/?); (B) We investigated the hypothesis that only high synchronizers (displayed in orange), but not low synchronizers (displayed in blue) show enhanced perception in certain phases of the motor rhythm by performing a logistic regression. (C) In experiment 1, speech production effects at 2 Hz were tested, in experiment 2, effects at the individual participants optimal rate were tested. In both experiments, the accuracy of the logistic regression was higher in higher synchronizers compared to lows, whereas only high synchronizers showed higher model accuracy compared to a null distribution. Adapted by permission from Springer Nature Publishing, Nature Human Behaviour, Speaking rhythmically can shape hearing, M.F. Assaneo*, J.M. Rimmele, Y. Sanz Perl, D. Poeppel, [COPYRIGHT Springer Nature] (2020).
Max Planck Institute for Empirical Aesthetics
