Abstract
Repeated exposure to the same stimulus results in an attenuated brain response in cortical regions that are activated during the processing of that stimulus. This phenomenon, called repetition suppression (RS), has been shown to be modulated by expectation. Typically, this is achieved by varying the probability of stimulus repetitions (Prep) between blocks of an experiment, generating an abstract expectation that ‘things will repeat’. Here, we examined whether stimulus-specific expectations also modulate RS. We designed a task where expectation and repetition are manipulated independently, using stimulus-specific expectations. We investigated to which extent such stimulus-specific expectations modulated the visual evoked response to objects in lateral occipital cortex (LOC) and primary visual cortex (V1), using functional magnetic resonance imaging (fMRI). In LOC, we found that RS interacted with expectation, such that repetition suppression was more pronounced for unexpected relative to expected stimuli. Additionally, we found that the response of stimulus-preferring voxels in V1 was generally decreased when stimuli were expected. These results suggest that stimulus-specific expectations about objects modulate LOC and propagate back to the earliest cortical station processing visual input.
Highlights
MethodsThe reaction time measurements collected during the behavioral task allowed us to probe whether expectation and repetition affected the behavioral response to the stimuli, and whether participants had learned the transition probabilities (cf Fig. 2)
Repeated exposure to the same stimulus results in an attenuated brain response in cortical regions that are activated during the processing of that stimulus
In lateral occipital cortex (LOC), we found that RS interacted with expectation, such that repetition suppression was more pronounced for unexpected relative to expected stimuli
Summary
The reaction time measurements collected during the behavioral task allowed us to probe whether expectation and repetition affected the behavioral response to the stimuli, and whether participants had learned the transition probabilities (cf Fig. 2) Aside from measuring these behavioral effects, this procedure ensured that participants were amply exposed to the trained stimulus transitions. Any voxels that, based on this selection procedure, came into consideration for both V1 and LOC were discarded entirely This ensured that there was no overlap between the ROIs. Reaction times during the behavioral experiment and the oddball trials during the fMRI experiment were analyzed using a 2 (expected versus unexpected) × 2 (repetition versus alternation) analysis of variance (ANOVA). We gauged potential modulatory effects of autistic personality traits on RS and ES using an analysis of covariance, whereby mean-centered AQ was entered as a covariate for the factors expectation, repetition, and hemisphere
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