VARIATION IN THE LATENCIES AND AMPLITUDES OF N400 AND NA AS A FUNCTION OF SEMANTIC PRIMING

The purpose of this study was to determine whether the latencies of tw o event-related potential (ERP) components, the NA and N400, were sens itive to semantic priming. Subjects performed a semantic judgment task , which was designed in such a way that the N400 could be examined wit hout overlap from the P3. Priming effects on the latencies of both NA and N400 were most apparent al frontocentral sites. The amplitude of N A was not significantly affected by priming. The amplitude of N400 was smaller for primed than for unprimed words, but the effect was signif icant only at centroposterior sites. Current source density (CSD) anal yses performed on the ERP data suggested the activation of multiple ge nerators in the N400 time region. The ERP and CSD data were consistent with the existence of two types of N400, a frontal N400 that varies i n latency as a Function of semantic priming, and a posterior N400 that varies in amplitude.