Expectancy constraints in degraded speech modulate the language comprehension network.

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• Speech comprehension relies on integrating auditory input with linguistic context.
• Semantic expectancy and auditory clarity influence how the brain processes spoken language.

Purpose of the Study:

• To investigate how semantic expectancy (cloze probability) and sentence intelligibility (noise vocoding) affect brain activity during speech comprehension.
• To map the neural basis of speech decoding and its modulation by linguistic predictability.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activation.
• Participants listened to sentences with varying intelligibility and semantic predictability.
• Analysis focused on activation patterns in the superior temporal sulci (STS), inferior frontal gyrus (IFG), and inferior parietal cortex (IPC).

Main Results:

• Intelligibility-modulated activation in the STS varied with cloze probability: extended in low-cloze, restricted in high-cloze sentences.
• Left inferior frontal gyrus (IFG) activation increased with intelligibility in low-cloze contexts.
• Left inferior parietal cortex (IPC) activation correlated with successful comprehension, whether driven by signal clarity or semantic context.

Conclusions:

• Auditory cortex activity in speech decoding regulates language-specific computations in the IFG and IPC.
• Semantic expectancy can modulate speech-decoding processes, reducing neural resource allocation for predictable sentences.
• Findings contribute to understanding the functional neuroanatomy of speech comprehension and the interplay between bottom-up and top-down processing.