Time course of semantic processes during sentence comprehension: an fMRI study

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• The human language system excels at generating novel meanings through word combinations.
• Understanding the neural basis of combinatorial semantic processing is crucial for language comprehension research.

Purpose of the Study:

• To investigate the neural correlates of combinatorial semantic processing using functional magnetic resonance imaging (fMRI).
• To differentiate brain activity related to single-word semantics versus the integration of word meanings into sentence-level semantics.

Main Methods:

• fMRI was employed to measure brain activity in participants performing a semantic rating task.
• Auditory stimuli included normal sentences, semantically incongruent sentences, pseudoword sentences, and their syntactically disrupted counterparts.
• Blood-oxygen-level-dependent (BOLD) signals were analyzed to identify brain regions involved in semantic processing.

Main Results:

• The left angular gyrus, left superior temporal sulcus, and left inferior frontal gyrus showed increased BOLD signal for real words versus pseudowords, indicating involvement in single-word semantic access.
• These word-level semantic effects were observed early in the hemodynamic response in the angular and inferior frontal gyri.
• The left angular gyrus and left lateral temporal lobe exhibited greater activation for normal sentences compared to semantically incongruent ones, reflecting combinatorial semantic processing.
• Combinatorial semantic effects emerged later in the hemodynamic response, after stimulus presentation.

Conclusions:

• Brain activity associated with word and sentence-level semantic information exhibits a complex spatiotemporal pattern.
• The left angular gyrus plays a significant role in processing the overall meaning of sentences.
• Distinct neural mechanisms underlie single-word semantic access and the integration of word meanings into complex sentence structures.