[Hemispheric difference in the time course of semantic activation: evidence from event-related potentials]

To investigate hemispheric differences of semantic activation, event-related potentials were recorded when two pairs of words were successively presented with a SOA of 200 ms or 800 ms. Each word pair was simultaneously exposed to the left (LVF) and right (RVF) visual fields. Participants were required to attend one visual field and make a judgment whether the words (prime-target) presented at the attended visual field were semantically related or not. A priming effect on reaction time was observed for RVF targets with SOA 200 ms, and for both LVF and RVF targets with SOA 800 ms, consistent with the idea that semantic activation is faster in the left than the right hemisphere. In contrast, the priming effect on N400 amplitude was not affected by the SOA and visual field, and the onset latency was shorter for RVF than for LVF targets, irrespective of SOA. The N400 priming effects were interpreted to be associated with task-induced semantic processing.