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 two 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.