May 9, 2021

Parametric cognitive load reveals hidden costs in the neural processing of perfectly intelligible degraded speech

Speech is often degraded by environmental noise or hearing impairment. People can compensate for degradation, but this is subjectively effortful. Previous research has identified frontotemporal networks involved in effortful perception, but so far has been unable to distinguish domain-general involvement in cognitive control from domain-specific involvement in speech perception. We overcame these limitations by measuring brain responses (via fMRI) to clear and degraded spoken sentences matched for intelligibility. On each trial, participants either attended to a sentence, or to a concurrent multiple object tracking task that imposed parametric cognitive load. Whereas the anterior insulae tracked domain-general task demands, anterior temporal cortex was selective to speech, with cognitive load revealing categorically different responses to clear speech and intelligibility-matched degraded speech. The results demonstrate that cognitive control is required to understand even very mildly degraded speech, underscoring the importance of interactions between perceptual and control systems for real-world speech comprehension.

 bioRxiv Subject Collection: Neuroscience

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