Familiarity and priming are mediated by overlapping neural substrates.

Explicit memory is widely assumed to reflect the conscious processes of recollection and familiarity. However, familiarity has been hypothesized to be supported by nonconscious processing. In the present functional magnetic resonance imaging (fMRI) experiment, we assessed whether familiarity is mediated by some of the same regions that mediate repetition priming, a form of nonconscious memory. Participants completed an implicit (indirect) memory task and an explicit (direct) memory task during fMRI. During phase I of each task, participants viewed novel abstract shapes with internal colored oriented lines and judged whether each shape was relatively "pleasant" or "unpleasant". During phase II of the indirect memory task, repeated (old) and new shapes were presented and participants made the same judgments. During phase II of the direct memory task, a surprise recognition test was given in which old and new shapes were presented and participants made "remember", "know", or "new" responses. Activity associated with priming was isolated by comparing novel versus repeated shapes during phase II of the indirect memory task. Activity associated with familiarity was isolated by comparing accurate "know" responses versus misses during phase II of the direct memory task. Priming and familiarity were associated with common activity within the superior parietal lobule and motor cortex, which we attribute to shared attentional and motor processing, respectively. The present fMRI results support the hypothesis that familiarity is supported by some of the same processes that support implicit memory.