The contribution of task-related factors to ERP repetition effects at short and long lags.

Event-related potentials (ERPs) were used to assess the relative contribution of task-related decision-making processes to the repetition effect at Lags 0 and 15. Electrophysiological activity was recorded from 16 subjects in two tasks. Task A required a lexical decision: subjects were instructed to silently count infrequently occurring nonwords in a list of words and nonwords. Task B, a recognition memory task presented in four blocks, required subjects to distinguish between old and new probes in each block. Significant ERP repetition effects, equivalent in both tasks, were found at Lag 0. In contrast, at Lag 15, the repetition effect was significant only in Task A. These results suggest that ERPs are sensitive primarily to poststimulus-identification sources of the repetition effect, such as the recovery of episodic traces related to stimulus-categorization and decision-making processes.