Human auditory cortex is sensitive to the perceived clarity of speech

Feedback connections among auditory cortical regions may play an important functional role in processing naturalistic speech, which is typically considered a problem solved through serial feed-forward processing stages. Here, we used fMRI to investigate whether activity within primary auditory cortex (PAC) is sensitive to the perceived clarity of degraded sentences. A region-of-interest analysis using probabilistic cytoarchitectonic maps of PAC revealed a modulation of activity, in the most primary-like subregion (area Te1.0), related to the intelligibility of naturalistic speech stimuli that cannot be driven by stimulus differences. Importantly, this effect was unique to those conditions accompanied by a perceptual increase in clarity. Connectivity analyses suggested sources of input to PAC are higher-order temporal, frontal and motor regions. These findings are incompatible with feed-forward models of speech perception, and suggest that this problem belongs amongst modern perceptual frameworks in which the brain actively predicts sensory input, rather than just passively receiving it.

► Abstract linguistic information modulates activity within primary auditory cortex. ► This effect is specific to degraded speech that is potentially intelligible. ► Reflects increased perceptual clarity resulting from knowledge-based cues. ► Is consistent with interactive, not feed-forward, accounts of speech perception.