Abstract
It is an established finding that neuronal activity is decreased for repeated stimuli. Recent studies revealed that repetition suppression (RS) effects are altered by manipulating the probability with which stimuli are repeated. RS for faces is more pronounced when the probability of repetition is high than when it is low. This response pattern is interpreted with reference to the predictive coding (PC) account, which assumes that RS is influenced by top-down expectations. Recent findings challenge the generality of PC accounts of RS by showing repetition probability does not modulate RS for other visual stimuli than faces. However, a number of findings on visual processing are in line with PC. Thus, the influence of repetition probability on RS effects during object processing requires careful reinvestigations. In the present fMRI study, object pictures were presented in a high (75%) or low (25%) repetition probability context. We found increased RS in the high-probability context compared to the low-probability context in the left lateral occipital complex (LOC). The dorsal-caudal and the ventral-anterior subdivisions of the LOC revealed similar neuronal responses. These results indicate that repetition probability effects can be found for other visual objects than faces and provide evidence in favor of the PC account.
Highlights
Repetition suppression (RS) is commonly defined as a diminished neural activation that results from the repeated presentation of a stimulus (Henson, 2003)
The objective of the current investigation was to examine whether stimulus repetition probability modulates RS effects during visual object processing in the lateral occipital complex (LOC)
To illustrate, pronounced RS effects could be found in the high-probability context (i.e., 21% signal decrease) whereas activation levels of repeated and alternate stimuli in the low-probability context do not differ in the current investigation
Summary
Repetition suppression (RS) is commonly defined as a diminished neural activation that results from the repeated presentation of a stimulus (Henson, 2003). The predictive coding (PC) model emphasizes the role of top-down influences on RS. According to this approach, information about a stimulus (e.g., an object) flows in a hierarchical manner from lower to higher cortical layers while expectations, which are built upon prior object regularities, are top-down backward influences which modulate the processing of the current object (Friston, 2005). Bottom-up flow of information and top-down expectations are compared at each level of hierarchical processing. From this perspective, RS occurs due to a correct prediction of the upcoming stimulus, that is, the currently processed object matches the expectation. RS effects reflect a smaller prediction error for expected stimuli, that is, decreased activation for repeated stimuli
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