Cognitive event-related potential components during continuous recognition memory for pictures.

Event-related brain potentials (ERPs) were recorded from 28 young adult subjects during a continuous recognition memory paradigm, with pictures as stimuli. Subjects were required to determine on each trial if the picture was "new" (never before presented) or "old" (seen previously). To assess differences between primary and secondary memory, old items were presented after lags of 2, 8, and 32 intervening pictures (equiprobable) following their first presentation. The results suggested that a negativity (Cz maximum) at 300 ms was the most likely candidate for the brain event reflecting the retrieval of the item from memory. Old/new effects were modulated by two types of activity, both of which were larger in the ERPs elicited by new items. The earlier of these, possibly similar to the N400, had a duration from about 250-600 ms, began with the N300 deflection, and lasted until "P300" began to decrement. The other was positive, resembled "positive slow wave," onset as P300 began to decrement, and lasted until the end of the recording epoch. There were no consistent effects of item lag on the behavioral data or on any of the ERP components, suggesting that for pictorial stimuli, the distinction between the two types of memory store, primary (i.e., immediate memory) and secondary (newly learned information), may not be relevant. In consonance with the lack of lag effects, it was suggested that the lack of a robust subsequent memory effect on the ERP waveform could have been due to the use of pictures, which may have required less elaborative processing in order to be encoded at input.