In bistable perception, ambiguous stimuli elicit spontaneous (endogenous) transitions between two mutually exclusive percepts while sensory stimulation remains constant. Such endogenous perceptual transitions have been studied in comparison with stimulus-induced changes in perception generated in a so-called “replay” condition. In the replay condition, perceptual transitions are created by a disambiguated version of the stimulus and designed to be as similar as possible to their ambiguous counterparts with respect to quality and timing. In a number of studies using functional magnetic resonance imaging (fMRI), the statistical comparison between endogenous and stimulus-induced perceptual transitions has shown that significantly higher “Blood Oxygen Level Dependent” (BOLD) responses in right hemispheric frontal and parietal brain areas are associated with endogenous perceptual transitions.
The functional role of this frontoparietal network has remained controversial, however. On the one hand, it has been argued that this enhanced activity might reflect causal influences of regions in frontal and parietal cortex on the processing in sensory brain areas and thus point to the importance of “top-down” processes for bistable perception. On the other hand, it has been proposed that differences in the BOLD signals measured might result from discrepancies in the perceptual quality of transitions between the two conditions. This “bottom–up” explanation focuses above all on possibly longer durations of perceptual transitions in the bistable as compared to the replay condition, being reflected by differences in frontoparietal activity.
The goal of this experiment was to disentangle these two hypotheses in a fMRI experiment on 15 healthy human participants. Using a rotating Lissajous figure, we elicited endogenous and stimulus-induced changes in perception, whereby participants rated the perceived duration of these events. Furthermore, we used “Statistical Parametric Mapping” (SPM) to test the BOLD activity associated with perceptual transitions in the bistable condition against the replay condition. Finally, we applied “Dynamic Causal Modeling” (DCM) in order to determine the neural model that most readily explains the observed BOLD signal in terms of effective connectivity.
We replicated previous findings of enhanced activity in frontoparietal brain regions for endogeneous perceptual transitions whilst controlling for potential confounds of differences in transition duration between the two conditions. Our DCM results indicated that enhanced activity for perceptual transitions during bistability is associated with a modulation of “top-down” connectivity from frontal to visual cortex.
Taken together, these findings suggest that activity in frontoparietal brain areas is crucially involved in perceptual transitions during bistable perception in terms of “top–down” connectivity.
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