The effect of stimulus predictability on the representations of local elements N Van Humbeeck, K Gijbels, T Putzeys, J Wagemans |
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Laboratory of Experimental Psychology, University of Leuven (KU Leuven), Belgium
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| Recent fMRI studies suggest that the presence of top-down predictions about a stimulus is associated with a reduced activation in lower brain regions in which more local features are represented, and increased activation in higher brain regions in which more global aspects of objects are encoded. This finding suggests that top-down feedback from higher areas reduces the activity in lower areas. There are several interpretations for this observed reduction in lower-level activity, involving either a weakening of neural representations of local image elements or a "sharpening" of local representations in which irrelevant lower-level activity is reduced. In this study, we aimed to investigate which interpretation is more likely. More specifically, we measured contrast perception of local gratings which are either part of a spatio-temporally coherent or incoherent stimulus configuration. Preliminary results indicate that the coherency of the stimulus reduces contrast discriminability, suggesting that neural representations of gratings are weakened when these gratings are part of a predictable spatio-temporal configuration. |
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