Context effects in a category verification task as assessed by event-related brain potential (ERP) measures.

This study examined the extent to which decisions about category membership (between category structure) are dependent on or dissociable from the typically structure (within category structure) of categories. To this end, behavioral and event-related brain potential (ERP) measurements were obtained in a category verification task that incorporated a context manipulation (list composition effect) that was previously shown to affect membership verification. In a German and an American English version of the experiment, pairs of words were presented and subjects were asked to decide whether or not the second word was an exemplar of the superordinate indicated by the first word. Both versions yielded similar results. The behavioral data showed that both typicality and context manipulation affected the verification times for the true exemplars. Furthermore, atypical true exemplars were affected more by context manipulation than mere typical ones. By contrast, the N400 component of the ERPs elicited by the true exemplars was influenced by typicality, but invariant in the face of the context manipulation. These results underscore the previously shown dissociation between reaction times and N400 changes and suggest that category membership decision (as reflected in verification times) and semantic relatedness or typicality of an exemplar (as reflected in N400 modulation) can vary independently from each other and, therefore, likely index the activity of different brain systems.