Lexical processing of visually and auditorily presented nouns and verbs: evidence from reaction time and N400 priming...

We investigated two aspects of lexical organization in normal adults employing behavioral and electrophysiological indices of semantic priming, namely: (1) Is there evidence for differential processing of nouns and verbs? (2) Is there evidence for separate systems for processing of orthographic and phonologic representations of words? Reaction time (RT), N400 amplitude and latency were used to examine the effect of semantic priming on lexical access of auditorily and visually presented nouns and verbs. We found that the temporal patterns of primed RTs and N400 latencies differed for nouns and verbs, indicating a functional difference in processing. However, the absence of topographic differences in N400 between nouns and verbs did not support anatomically distinct representations of these word classes. By contrast, a modality-specific topography at N400, in addition to RT and N400 amplitude differences between auditory and visual conditions, supported the proposed separation of the orthographic and phonologic representations of words. The implications of the findings for general theories of lexical organization are discussed.