Early components of event-related potentials related to semantic and syntactic processes in the Japanese language

Brain activities were compared between semantic and syntactic processing in the Japanese language using event-related potentials with a 58-ch EEG system. We previously found that semantic violations elicited N400 and syntactic violations elicited P600 but not early left anterior negativity (ELAN) or left anterior negativity (LAN) using a relatively long stimulus presentation time (1 s). In the present study, we adopted a shorter stimulus presentation time (0.5 s), which might impose a heavier burden on the working memory system, to test the possible relevance of load on the working memory system to ELAN/LAN. A global field power analysis showed an increased potential field strength at the latency of 320 ms in either type, as well as those at the later latencies reflecting N400 (556 ms) and P600 (712 ms). Statistical analyses revealed a significant negative deflection in the right frontal region for the semantic type, whereas no significant deflection in either specified region was obtained for the syntactic type at the latency of 320 ms. The lack of ELAN/LAN suggested that it was not due to the deactivation of the working memory system. Moreover, scalp current density topographies implied that the processing of the verbal stimuli was mediated by distinct areas within the left temporal region, according to its semantic congruency with the preceding context at a latency as early as 320 ms. These findings are in line with the dual-route hypothesis of reading, which suggests that the reading of verbal stimuli semantically incongruent with the preceding context is dominated by phonological processes rather than lexico-semantic.