Expectation modulates repetition priming under high stimulus variability.

Neural responses to stimuli are often attenuated by repeated presentation. When observed in blood oxygen level-dependent signals, this attenuation is known as fMRI adaptation (fMRIa) or fMRI repetition suppression. According to a prominent account, fMRIa reflects the fulfillment of perceptual expectations during recognition of repeated items (Summerfield, Trittschuh, Monti, Mesulam, & Egner, 2008). Supporting this idea, expectation has been shown to modulate fMRIa under some circumstances; however, it is not currently known whether expectation similarly modulates recognition performance. To address this lacuna, we measured behavioral and fMRI responses to faces while varying the extent to which each stimulus was informative about its successor. Behavioral priming was greater when repetitions were more likely, suggesting that recognition was facilitated by the expectation than an item would repeat. Notably, this effect was only observed when stimuli were drawn from a broad set of faces including many ethnicities and both genders, but not when stimuli were drawn from a narrower face set, thus making repetitions less informative. Moreover, expectation did not modulate fMRIa in face-selective cortex, contrary to previous studies, although an exploratory analysis indicated that it did so in a medial frontal region. These results support the idea that expectation modulates recognition efficiency, but insofar as behavioral effects of expectation were not accompanied by fMRI effects in visual cortex, they suggest that fMRIa cannot be entirely explained in terms of fulfilled expectations.