Category Membership and Semantic Coding in the Cerebral Hemispheres.

Area of Science:

• Cognitive Neuroscience
• Psycholinguistics
• Neuroscience

Background:

• Semantic categories possess an internal gradient of membership, with typical items more central than peripheral ones.
• Previous research has yielded mixed results regarding hemispheric differences in processing this category gradient.

Purpose of the Study:

• To empirically investigate whether the left and right brain hemispheres process semantic category gradients differently.
• To explore alternative theoretical interpretations of observed hemispheric differences in semantic processing.

Main Methods:

• Two experiments were conducted where participants categorized words presented to either the left visual field/right hemisphere or right visual field/left hemisphere.
• Stimuli included category names and either closely or distantly related words to assess typicality effects and category boundaries.

Main Results:

• Distantly related words were categorized slower in the right hemisphere (LVF/RH) compared to the left hemisphere (RVF/LH).
• No significant difference in categorization speed was observed for words close to the category prototype.
• Both hemispheres demonstrated consistent category boundaries when evaluating items near the fuzzy border of category membership.

Conclusions:

• The findings reveal a distinct typicality effect in the right hemisphere, indicating a specialized role in processing the gradient of semantic category membership.
• The consistent category boundaries across hemispheres suggest shared mechanisms for defining category limits.
• The results favor a processing explanation over a structural one for observed hemispheric differences in semantic categorization.