More ways than one: ERPs reveal multiple familiarity signals in the word frequency mirror effect.

Recent dual-process models of the word frequency mirror effect place absolute familiarity, an item׳s baseline familiarity at a given time point, as responsible for false alarm differences and recollection for hit rate differences between high and low frequency items. One of the earliest dual-process propositions, however, posits an additional relative familiarity mechanism which is sensitive to recent presentation but relative to the absolute familiarity of a particular item (Mandler, 1980). In this study, it was possible to map these three mechanisms onto known event-related potential (ERP) effects in an old/new recognition task with high and low frequency words. Contrasts between ERPs elicited by high and low frequency new items were assumed to index absolute familiarity, and the distribution of this effect from 300 to 600ms was topographically distinct from a temporally-overlapping midfrontally-distributed old/new effect which was larger for low than high frequency words, as would be expected from a relative familiarity mechanism. A later left parietal old/new effect, strongly linked to recollection, was only present for low frequency items. These frequency-sensitive amplitude differences for both old/new effects disappeared in a second recognition task in which old/new decisions were made under a time constraint, although the posterior absolute familiarity effect remained unaffected by the speeding of responses. The data support the assertion that three distinct recognition processes are affected by word frequency in recognition memory tasks, and the qualitatively distinct distributions associated with the two familiarity contrasts support the presence of two cognitively distinct familiarity mechanisms.