The effect of immediate and delayed word repetition on event-related potential in a continuous recognition task.

The dissociation of immediate and delayed word repetition was studied using a continuous recognition memory task and event-related potential (ERP). Among 240 stimulus words, 40 words were not repeated, 100 were immediately repeated and 100 were repeated after 5 intervening words. Words presented only once during the experiment were referred to as new words. Subjects responded faster and more accurately to words repeated immediately than to new words and to words repeated after a delay. In terms of ERP results, immediate repetition was associated with large P300 amplitude, early P300 latency and the absence of N400, while delayed repetition was associated with small P300 amplitude, late P300 latency and the presence of N400. N400 was elicited only to new words and to those repeated after intervening words. The general morphology of the waveforms was similar for two repetition conditions until around 310 ms after the onset of stimulus. These results indicate that distinct neural systems subserve the immediate and delayed repetition effect, and that the difference between the two emerges around 310 ms poststimulus. Immediate and delayed word repetition are considered in terms of template matching and memory searching, and are possibly mediated by the parietal and left medial temporal lobes, respectively.