Electrophysiological correlates of familiarity in recognition memory and exclusion tasks

ERPs were acquired in the test phases of three memory experiments, where three classes of word were presented. These were: (i) words encountered in a prior study phase (studied words), (ii) words presented at test for the first time (new words), and (iii) new words repeated after a lag of 7-9 intervening words (repeated test words). In experiments 1 and 2, participants were asked to respond on one key to studied words and on another to new as well as to repeated test words. In experiment 3, a binary response was again required, but in this case repeated test and studied words were assigned to the same key. In each experiment, the principal focus for analysis was on the differences between the ERPs at mid-frontal electrode locations from 300 to 500 ms post-stimulus that were associated with incorrect responses to studied words (misses) and correct responses to new words. It has been proposed that relatively greater positivity for studied than for new words at this locus reflects the greater familiarity of studied than of unstudied words. ERPs elicited by misses were reliably more positive-going than those elicited by correct rejections in experiments 1 and 2 only. These findings support the link between this modulation of the electrical record and familiarity in so far as the designs of the experiments lead to the prediction that the average level of familiarity associated with misses should be higher in the first two experiments than in the third. In combination with findings in other studies, these data support dual-process accounts of recognition memory.