Event-related potentials during conscious and automatic memory retrieval

The effects of study-test lags of between 0 and 32 items on conscious (C) a nd automatic (A) memory processes in a running word-completion task were in vestigated with event-related potentials (ERPs). The process dissociation p rocedure (PDP) can distinguish between C and A contributions to memory by c omparing performance when subjects respond with either an old item (inclusi on) or a new item (exclusion). C can be estimated by subtracting the probab ility of an intrusion of an old item during the exclusion task (due to A wi thout C) from the probability of correctly producing an old item during the inclusion task (due to C and/or A). The behavioral results showed that C w as stronger when the test item followed the studied word in the next trial or after a lag of one stimulus. The strength of A did not vary with lag. Th e ERP waveforms contained a broad parietal positive wave between 300 and 80 0 ms. This parietal wave distinguished between correctly recalled old and n ew words. The early portion of this old-new effect was significantly affect ed by lag. Subtracting waveforms to obtain a measure of C revealed an effec t in the later portion of this wave, lateralized over the left hemisphere. A sustained frontal negativity occurred during all recordings and was large r during conscious retrieval. There was no consistent ERP effect related to automatic memory retrieval. (C) 2000 Elsevier Science B.V. All rights rese rved.