Motor engagement relates to accurate perception of phonemes and audiovisual words, but not auditory words

Kelly Michaelis,Makoto Miyakoshi,Andrei V Medvedev,Gina Norato,Peter E Turkeltaub

doi:10.1038/s42003-020-01634-5

Abstract

A longstanding debate has surrounded the role of the motor system in speech perception, but progress in this area has been limited by tasks that only examine isolated syllables and conflate decision-making with perception. Using an adaptive task that temporally isolates perception from decision-making, we examined an EEG signature of motor activity (sensorimotor μ/beta suppression) during the perception of auditory phonemes, auditory words, audiovisual words, and environmental sounds while holding difficulty constant at two levels (Easy/Hard). Results revealed left-lateralized sensorimotor μ/beta suppression that was related to perception of speech but not environmental sounds. Audiovisual word and phoneme stimuli showed enhanced left sensorimotor μ/beta suppression for correct relative to incorrect trials, while auditory word stimuli showed enhanced suppression for incorrect trials. Our results demonstrate that motor involvement in perception is left-lateralized, is specific to speech stimuli, and it not simply the result of domain-general processes. These results provide evidence for an interactive network for speech perception in which dorsal stream motor areas are dynamically engaged during the perception of speech depending on the characteristics of the speech signal. Crucially, this motor engagement has different effects on the perceptual outcome depending on the lexicality and modality of the speech stimulus.

Highlights

A longstanding debate has surrounded the role of the motor system in speech perception, but progress in this area has been limited by tasks that only examine isolated syllables and conflate decision-making with perception
The present study addresses these issues in the following ways: (1) comparing perception of speech and non-speech environmental sounds, (2) comparing phonemes and whole words, (3) comparing auditory-only words and audiovisual words, (4) employing adaptive staircase procedures to hold difficulty constant at two levels (Easy and Hard) and controlling for difficulty across stimulus types, and (5) focusing on perception by using large sets of stimuli and temporally separating stimulus perception from answer choice presentation and response
While there were no significant interactions, the mixed-effects model revealed an effect of difficulty, indicating that the Easy and Hard levels were significantly different within stimulus types

Summary

Introduction

A longstanding debate has surrounded the role of the motor system in speech perception, but progress in this area has been limited by tasks that only examine isolated syllables and conflate decision-making with perception. The idea that representations of speech sounds in motor areas (including primary motor cortex, premotor cortex, and Broca’s area (BA44/45)) provide a template for decoding incoming input is especially common in studies investigating noisy or degraded speech[12,16,17,20,21,22,23] These motor modeling theories lead to two predictions: (1) that motor activity during perception should be specific to speech or other “doable sounds” that we have practiced articulatory plans for producing, and (2) that motor involvement depends on the task context and stimulus features. In order to understand whether the motor system participates in perception in real-world scenarios, it is crucial to examine motor activity during whole word perception

Methods

Results

Conclusion