Dissociating memory processes involved in direct and indirect tests with ERPs to unfamiliar faces

Event-related potentials (ERPs) were recorded during indirect and direct memory tests for unfamiliar faces. In both tests, ERPs displayed the usual positive shift known as the ERP repetition effect. In the indirect test, this effect includes parietal effect (the usual N400 effect) and a right fronto-central effect. Both effects are also present in the direct test. Two additional effects are present only in the direct test. These effects are an early fronto-polar effect and a late posterior effect (the usual P600 effect). These findings are taken as support for the distinction between 'associative' processes elicited in both the direct and indirect tests, and 'episodic' processes elicited only in the direct test. This task dissociation could well provide a scalp correlate of the distinction between the neocortical and cortico-limbic systems that have been shown to contribute respectively to associative and episodic processing. In addition, it is proposed that the dissociation between the two frontal effects could be accounted for by a distinction between the processing of intrinsic vs. extrinsic contextual attributes as a function of the task requirements.