Antithetical contribution of primary and non-primary auditory cortex while listening to speech in noisy scenes

Abstract

Invasive and non-invasive electrophysiological measurements during "cocktail-party"-like listening indicate that neural activity in the human auditory cortex (AC) "tracks" the envelope of relevant speech. Due to the measurements limited coverage and/or spatial resolution, however, the distinct contribution of primary and non-primary auditory areas remains unclear. Using 7-Tesla fMRI, here we measured brain responses of participants attending to one speaker, without and with another concurrent speaker. Using voxel-wise modeling, we observed significant speech envelope tracking in bilateral Heschls gyrus (HG) and right middle superior temporal sulcus (mSTS), despite the sluggish fMRI responses and slow temporal sampling. Neural activity was either positively (HG) or negatively (mSTS) correlated to the speech envelope. Further analyses comparing the similarity between spatial response patterns in the concurrent speakers and single speaker conditions indicated that whereas tracking in HG reflected both relevant and (to a lesser extent) non-relevant speech, right mSTS selectively represented the relevant speech signal. Additionally, in right mSTS, the similarity strength correlated with the participants comprehension of relevant speech. These results indicate that primary and non-primary AC antithetically process ongoing speech suggesting a push-pull of acoustic and linguistic information.