Abstract
Event-related brain potentials (ERPs) were recorded to investigate the sensitivity of N400 to attentional focusing on a specific representation in lexicon. Twelve subjects were required to detect a nonword preceded by a specific word in a series of successively presented words and nonwords. In this task, subjects intentionally kept attention to the particular word until that word was presented. According to two-process theories of attention (for example, Posner & Snyder, 1975), controlled attention to a specific word results in activation of the corresponding representation in lexicon, which is accompanied by inhibition of other representations. If the amplitude of N400 would reflect the activation level in lexicon, the N400 attenuation based on the semantic relation between two successive words would not be observed when subjects attend to a specific word, and the activation is limited to that word. The result, however, did not support this prediction. The N400 was smaller when the stimulus was preceded by a semantically related word than when preceded by an unrelated word, although N400 attenuation was small compared to when subjects' attention was not focused on any words. These suggested that N400 was more sensitive to the semantic integration of the word into the preceding context than to the attentional focusing in lexicon.
