Binocular rivalry: frontal activity relates to introspection and action but not to perception.
When two dissimilar stimuli are presented to the eyes, perception alternates between multiple interpretations, a phenomenon dubbed binocular rivalry. Numerous recent imaging studies have attempted to unveil neural substrates underlying multistable perception. However, these studies had a conceptual constraint: access to observers' perceptual state relied on their introspection and active report. Here, we investigated to what extent neural correlates of binocular rivalry in healthy humans are confounded by this subjective measure and by action. We used the optokinetic nystagmus and pupil size to objectively and continuously map perceptual alternations for binocular-rivalry stimuli. Combining these two measures with fMRI allowed us to assess the neural correlates of binocular rivalry time locked to the perceptual alternations in the absence of active report. When observers were asked to actively report their percept, our objective measures matched the report. In this active condition, objective measures and subjective reporting revealed that occipital, parietal, and frontal areas underlie the processing of binocular rivalry, replicating earlier findings. Furthermore, objective measures provided additional statistical power due to their continuous nature. Importantly, when observers passively experienced rivalry without reporting perceptual alternations, a different picture emerged: differential neural activity in frontal areas was absent, whereas activation in occipital and parietal regions persisted. 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.
Department of Neurophysics, Philipps-University, 35032 Marburg, Germany; Section BrainImaging, Department of Psychiatry and Psychotherapy, Philipps-University, 35037 Marburg, Germany; Vision Sciences Laboratory, Harvard University, Cambridge, Massachusetts 02138; Cognitive Psychology Unit, Leiden University, 2333AK Leiden, The Netherlands; Leiden Institute for Brain and Cognition, Leiden, 2300RC Leiden, The Netherlands and Center for Interdisciplinary Research, 33615 Bielefeld, Germany.
Stefan
S
Frässle
Jens
J
Sommer
Andreas
A
Jansen
Marnix
M
Naber
Wolfgang
W
Einhäuser
D000293:Adolescent; D000328:Adult; D005260:Female; D005625:Frontal Lobe / Q000098:blood supply / Q000502:physiology*; D006801:Humans; D008297:Male; D055815:Young Adult