Poster A101, Saturday, March 24, 1:30–3:30 pm, Exhibit Hall C
Parieto-frontal regions and alpha power involved in postdiction
Laetitia Grabot1, Virginie van Wassenhove1; 1CEA, NeuroSpin, Cognitive Neuroimaging Unit
Current hypotheses suggest that perception results from the integration of discretized neural sequences. In postdiction, a stimulus arriving late can retro-actively influence the perception of an earlier stimulus, as in the Rabbit illusion, in which the intermediate flash in a sequence of 3 flashes is spatially mislocalized due to the temporal regularity of the sequence. The possible implication of oscillatory mechanisms in postdiction has been surprisingly unexplored despite the fundamental role of timing in this phenomenon. While computational models have proposed that postdiction arises from top-down expectations, no empirical evidence has yet been provided. Here, we tested this hypothesis by using the Rabbit illusion in a combined MEG-EEG study. The inter-stimulus interval of visual sequences was calibrated so that a given physical sequence yielded ~50% correct and ~50% illusory perceptual outcomes. This design allowed comparing different percepts elicited by the same stimulation. First, we observed that, when the illusion was perceived, parieto-frontal regions were more activated after the last stimulus. This finding validates the notion of posterior representational updating. Second, the analysis of oscillatory activity showed an increase of pre- and post-stimulus alpha power, in visual regions, predicting the illusory perception of the sequence. Increased attention, indexed by a decrease in alpha power, may reduce the sensory uncertainty of the spatial location of the intermediate stimulus. Overall, our results suggest that high-order areas may contribute to the postdictive reconstruction of a visual sequence, consistent with the hypothesis that the Rabbit illusion results from uncertain sensory evidence combined with prior expectations.
Topic Area: PERCEPTION & ACTION: Vision