Bilateral speech comprehension reflects differential sensitivity to spectral and temporal features

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Speech Processing

Background:

• Speech comprehension is bilateral, but specific roles of left and right auditory cortices are unclear.
• Previous hypotheses suggest left areas process temporal aspects and right areas process spectral aspects of sound.
• These hypotheses lacked direct testing in speech or music domains.

Purpose of the Study:

• To investigate the functional distinction between left and right auditory cortices in speech comprehension.
• To test the hypothesis of differential processing of temporal and spectral speech signal features.
• To provide direct evidence for hemispheric specialization in auditory speech processing.

Main Methods:

• Used brain imaging (fMRI) with a parametric design manipulating speech signals.
• Independently altered spectral and temporal domains of the speech signal using noise-band vocoding.
• Assessed word comprehension and brain activation across five degradation levels for each domain.

Main Results:

• Identified a functional distinction in auditory association cortices: left anterolateral superior temporal sulcus (STS) responded to temporal detail.
• Right auditory homolog areas showed greater sensitivity to spectral detail variations.
• Behavioral measures confirmed stronger coupling between spectral detail changes and STS BOLD signal.

Conclusions:

• Provides direct evidence for distinct roles of left and right auditory cortices in speech comprehension.
• Left hemisphere preferentially processes temporal acoustic information, while the right hemisphere processes spectral information.
• Suggests complementary roles for left and right superior temporal sulci in understanding speech.