Interaction between process and content in semantic memory: an fMRI study of noun feature knowledge.

Effective semantic processing requires both stored conceptual knowledge and the ability to relate this information to our environment. In the current study we examined how neural processing of a concept's features was modulated by the semantic context in which they were presented using two types of nouns: complex nouns, in which all features contribute in a variable manner to an object's meaning (apples are usually red, but not always), and nominal kinds, for which a single feature plays a diagnostic role (an uncle must be the brother of a parent). We used fMRI to monitor neural activity while participants viewed a list of features and decided whether the list accurately described a target concept. We focused on the effect of semantic context on processing of features critical to a concept's representation. Task demands were manipulated by giving participants instructions that encouraged rule-based or similarity-based judgments. Activation patterns for feature processing were found to depend on the type of noun being evaluated and whether or not critical features were consistent with surrounding information: When processing critical features that contradicted other information, complex nouns resulted in additional recruitment in frontal and temporal cortex compared to nominal kinds. We observed modest effects of instruction condition, with rule-based instructions resulting in increased frontal processing and similarity-based instructions recruiting more temporal and parietal regions. Together, these results support the hypothesis that various classes of nouns are represented differently in semantic memory, and emphasize the dynamic interaction of process and content in semantic memory.