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Abstract:
Neuroimaging studies examining cortical recruitment during
language tasks have reported distributed areas of activation,
frequently including temporal regions. However, variations across
experiments in type of stimuli and task demands have made results
difficult to assess. In this BOLD fMRI study we distinguish between
semantic content and processing with separate tasks performed on a
single class of verbal stimuli. For Task 1, healthy young subjects
judged consecutively presented written animal terms for
"pleasantness," similarly judging pseudofont strings as a control.
This task promotes deep semantic processing, introduces minimal
cognitive demands, and allows a uniform task for experimental and
control stimuli. For Task 2, subjects made animal category
membership decisions of similarly presented words for animals and
non-animals (e.g., fruits), judging pseudofont strings for the
presence of a particular character as a control. Task 1, which
tapped semantic content, recruited bilateral occipital and left
posterior temporal areas. Task 2, a categorical decision-making
process, recruited those areas plus left anterior temporal and
prefrontal areas. Contrasts of pleasantness judgments minus
category membership decisions (each minus its baseline) revealed
bilateral occipital recruitment; category membership decisions
minus pleasantness judgments revealed left prefrontal recruitment.
These results emphasize the importance of considering the semantic
content of a category of knowledge as well as the process by which
semantic content is probed.
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