# Effects of speech periodicity and speech rate on auditory-motor coupling during speech comprehension

## TL;DR

The study finds that natural, less periodic speech rhythms improve comprehension by enhancing brain coupling between auditory and motor areas.

## Contribution

The paper introduces a novel analysis of how speech periodicity and rate independently affect auditory-motor coupling and comprehension.

## Key findings

- Faster syllabic rates and lower periodicity are linked to stronger coupling between pSTG and motor areas.
- Comprehension improves with lower periodicity and declines at faster speech rates.
- Natural speech rhythms may optimize coupling and comprehension through a balance of auditory and motor processing.

## Abstract

According to neural oscillatory accounts, periodicity at the syllabic scale enhances speech comprehension through theta brain rhythms. Natural speech, however, is not strictly periodic and stronger periodicity, such as under conditions of fast speech, may hinder comprehension. Using magnetoencephalography, we investigate how natural variation in syllabic-level periodicity affects comprehension and auditory-motor coupling in brain areas related to temporal speech processing. We model speech periodicity and rate independently. Theta-band phase coupling between the posterior superior temporal gyrus (pSTG) and speech motor areas is assessed using Gaussian-Copula Mutual Information (GCMI). We find that faster syllabic rates and lower periodicity are associated with stronger coupling between the pSTG and inferior precentral gyrus, but also inferior frontal gyrus and supplementary motor areas. Comprehension improves with lower periodicity and declines at faster rates. The syllabic rate and periodicity moderate the coupling-comprehension relationship, possibly reflecting a complex interplay of lower-level auditory processing and higher-level prediction from the speech motor cortices. These findings suggest a sweet spot for natural, less periodic speech rhythms that support optimal processing and emphasize the necessity to investigate natural speech.

A sweet spot for natural, less periodic speech rhythms, indicated by stronger coupling between auditory cortex and speech motor areas and enhanced comprehension, may relate to a complex interplay of lower-level auditory processing and higher-level prediction from the speech motor cortices.