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Stefan Frässle, Jens Sommer, Marnix Naber, Andreas Jansen, Wolfgang Einhäuser; Neural Correlates of Binocular Rivalry as measured in fMRI are partially confounded by observers' active report. Journal of Vision 2013;13(9):937. doi: 10.1167/13.9.937.
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© ARVO (1962-2015); The Authors (2016-present)
When different stimuli are presented to either eye, perception alternates between distinct interpretations, a phenomenon dubbed binocular rivalry. Numerous recent imaging studies have attempted to unveil neural substrates underlying binocular rivalry. However, most rivalry studies are bedeviled by a major methodological constraint: access to observers' perceptual state typically relies on introspection and active report (e.g., by button presses). Here we ask to what extent the observed neural correlates of rivalry are confounded by such subjective measures. We here used two reflexes, the gain of the optokinetic nystagmus (OKN) and pupil dilation, to objectively and continuously map perceptual alternations for dynamic and stationary rivalry stimuli. Using these two objective measures during functional magnetic resonance imaging, we could, for the first time, control for confounding influences of active report and introspection on the neural activity during rivalry. In all conditions, rivalry stimuli were contrasted against identical stimuli presented to both eyes whose alternation rate was matched to the endogenous alternations during preceding rivalry trials. We find that, when observers are asked to actively report their percept like in standard binocular rivalry paradigms, our objective measures are consistent with report. In this active condition, both objective measures and button presses identify occipital, parietal and frontal areas to underlie the processing of binocular rivalry. Although the objective measures provide additional statistical power due to their continuous nature, these results confirm earlier studies. Importantly, however, when observers passively experience rivalry without reporting alternations, a different picture emerges: differential neural activity in middle frontal areas is absent, whereas activation in parietal and occipital regions persists. Our results question the popular view of a driving role of frontal areas in the initiation of perceptual alternations during binocular rivalry. Instead, we conclude that frontal areas are associated with active report and introspection rather than with rivalry per se.
Meeting abstract presented at VSS 2013
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