Hierarchy of Auditory Cortex Adaptation to Signal Degradation. From Acoustics to Prediction

Abstract

The brain does not process speech as a single stream. Instead, it operates across multiple levels at once — acoustic, voice-selective, prosodic, and multisensory — and each level has its own way of compensating when the signal degrades, whether through noise vocoding, disrupted binaural hearing, or peripheral deafness. This review brings together evidence showing that: (1) the bilateral superior temporal gyrus responds to acoustic degradation largely regardless of whether speech is intelligible; (2) the temporal voice areas (TVA) stay tuned to voices even under severe degradation, drawing on preserved temporal cues; (3) visual prosodic facial movements generate predictive auditory representations before the acoustic signal even arrives; and (4) bilateral cochlear implants normalize cortical activity patterns more effectively than a single implant. Drawing on fMRI, PET, and EEG data, we propose an integrative model of hierarchical cortical adaptation and consider what it means for auditory rehabilitation.