The influence of response-time demands on electrophysiological correlates of successful episodic retrieval.

Event-related potentials (ERPs) were acquired in two memory retrieval tasks. In Experiment 1 a 2.5 s response-time limit was imposed at test, while in Experiment 2 there was no explicit upper limit. There were no other structural differences between the two experiments. The response-time manipulation did not influence the accuracy of memory judgements, but resulted in qualitative changes in the ERP old/new effects that were elicited in the two tasks. In Experiment 2, the ERP old/new effects from 700 ms post-stimulus onwards comprised a relatively greater positivity for correct judgements to old items in comparison to correct judgements to new items. In keeping with findings in previous studies, this relative positivity was largest at anterior sites over the right hemisphere. In Experiment 1, by contrast, the ERP old/new effects during the same time window were most prominent at right hemisphere central electrode locations, and comprised a relatively greater positivity for correct judgements to new rather than to old test items. In combination, the findings in the two experiments are consistent with the view that the imposition of different response-time demands results in the engagement of neurally and functionally distinct processes during episodic retrieval. The time course of these distinct ERP old/new effects suggests that different post-retrieval monitoring operations were engaged according to the time available to make memory judgements.