Binocular Rivalry: Frontal Activity Relates to Introspection and Action But Not to Perception

Abstract

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.

Rivalry-Like Neural Activity in Primary Visual Cortex in Anesthetized Monkeys

“…Our anesthetized preparation also provided several unique advantages for this type of studies. First, one does not need to worry about conscious-related influences, or extra signals generated by introspection or active reporting (e.g., Frässle et al, 2014). Second, compared with awake subjects, anesthetized preparations provide more stable eye positions, no eye blinks, longer imaging time and a lower noise level, which were all important for the successful single-trial analysis in this study.…”

“…1D). Each raw L-R signal was first detrended by subtracting a fourth polynomial fitting (Tanabe et al, 2002;Friman et al, 2004). Each FFT power spectrum was then normalized to its frequency response at 0.25 Hz in the stimulus-alternation condition.…”

Future directions for identifying the neural correlates of consciousness

“…Along the lines of what we have previously argued [2][3][4] , the authors emphasize the role of sensory areas as prime candidates for neural correlates of consciousness (NCC). However, although visual conscious experience certainly appears to be related to activity in the posterior cortical regions, this is probably not the case for conscious experiences within other sensory domains where perceptual processing does not take place in the posterior cortex -the gustatory cortex, for instance, is located partly in the frontal lobe.…”

A Common Mechanism for Perceptual Reversals in Motion-Induced Blindness, the Troxler Effect, and Perceptual Filling-In

“…'' It is important to note that given the primary dependent measures in the current study relied on subjective reports, it is difficult to directly determine whether the observed correlations were driven by a common perceptual mechanism or by systematic variation in the participants' decision criterion (i.e., their willingness to report an illusory disappearance). The subjective nature of illusory disappearances, and other phenomena of multistability, is a well-known experimental challenge (e.g., Caetta, Gorea, & Bonneh, 2007;Fra¨ssle, Sommer, Jansen, Naber, & Einha¨user, 2014;Mamassian & Goutcher, 2005), and a variety of approaches have been used to offer insight. For example, optokinetic nystagmus and pupil reflex have been used as objective measures of perceptual switches in binocular rivalry (Fra¨ssle et al, 2014), showing neural activity associated with perceptual rivalry in the absence of self-report responses.…”