Semantic categorization and event-related potentials.

The N400 component of the event-related brain potential (ERP) was examined by presenting subjects with a series of words belonging to the same category and a series of declarative sentences. Half of the word series ended with a semantically unrelated word, while half of the sentences ended with a semantically inappropriate word. In the first experiment, subjects were instructed to read the word series and sentences, while in the second experiment they were instructed to indicate whether the word series or sentences ended appropriately or not with a button-press response. Word series and sentences with semantically incongruous endings produced a robust negative component at 400 msec followed by a positive-going wave for both the reading and decision tasks. When the subjects were required to categorize the word series and sentences endings, the negative component was followed by a robust P3 in both conditions. Analysis of scalp amplitude distributions for each task taken in conjunction with previous findings suggests that the semantically induced N400 component is most likely a "generic" N2. The relationship between the N2, N400, and P3 is discussed.