N400 effects of semantic richness can be modulated by task demands.

Semantic richness is a multidimensional construct that can be defined as the amount of semantic information associated with a concept. OBJECTIVE To investigate neurophysiological correlates of semantic richness information associated with words and its interaction with task demands. METHOD Two different dimensions of semantic richness (number of associates and number of semantic neighbors) were investigated using event-related potentials (ERPs) in lexical decision (LDT) and semantic categorization tasks (SCT) using the same stimuli in 2 groups of participants (24 in each group). RESULTS The amplitude of the N400 ERP component, which is associated with semantic processing, was smaller for words with a high number of associates (p = .003 at fronto-centro-parietal sites) or semantic neighbors (p < .03 at centro-parietal sites) than for words with a low number of associates or number of semantic neighbors, in the LDT but not the SCT. CONCLUSIONS These results suggest that the effects of semantic richness vary with task demands and may be used in a top-down manner to accommodate the current context. (PsycINFO Database Record