Journal of Neuroscience vol:33 issue:23 pages:9805-9812
Previously several functional magnetic resonance imaging (fMRI) studies point toward the role of perceptual expectations in determining
adaptation or repetition suppression (RS) in humans. These studies showed that the probability of repetitions of faces within a block
influences the magnitude of adaptation in face-related areas of the human brain (Summerfield et al., 2008). However, a current macaque
single-cell/local field potential (LFP) recording study using objects as stimuli found no evidence for the modulation of the neural response
by the repetition probability in the inferior temporal cortex (Kaliukhovich and Vogels, 2010). Here we examined whether stimulus
repetition probability affects fMRI repetition suppression for nonface object stimuli in the human brain. Subjects were exposed to either
two identical [repetition trials (RTs)] or two different [alternation trials (ATs)] object stimuli. Both types of trials were presented blocks
consisting of either 75% [repetition blocks (RBs)] or 25% [alternation blocks (ABs)] of RTs. We found strong RS, i.e., a lower signal for
RTs compared to ATs, in the object sensitive lateral occipital cortex as well as in the face-sensitive occipital and fusiform face areas.
More importantly, however, there was no significant difference in the magnitude of RS between RBs and ABs in each of the areas.
This is in agreement with the previous monkey single-unit/LFP findings and suggests that RS in the case of nonface visual objects
is not modulated by the repetition probability in humans. Our results imply that perceptual expectation effects vary for different
visual stimulus categories.