Regulating the Access to Awareness: Brain Activity Related to Probe-related and Spontaneous Reversals in Binocular Rivalry.

The P3b brain wave, previously linked to visual awareness, is associated with updates in conscious perception rather than with processing external stimuli themselves. In a binocular rivalry experiment, participants viewed competing images, one per eye, and brief probes were flashed over the dominant or suppressed image. The timing of the P3b wave corresponded to when participants reported a perceptual switch, not to when the probe occurred. This supports the idea that P3b signals a change in what is consciously perceived. The amplitude of an earlier wave, the P1, predicted how quickly a perceptual reversal happened, and the amplitude of the P3b predicted the duration of a mixed-percept stage.

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Abstract

Research on the neural correlates of consciousness (NCC) has implicated an assortment of brain regions, ERP components, and network properties associated with visual awareness. Recently, the P3b ERP component has emerged as a leading NCC candidate. However, typical P3b paradigms depend on the detection of some stimulus change, making it difficult to separate brain processes elicited by the stimulus itself from those associated with updates or changes in visual awareness. Here we used binocular rivalry to ask whether the P3b is associated with changes in awareness even in the absence of changes in the object of awareness. We recorded ERPs during a probe-mediated binocular rivalry paradigm in which brief probes were presented over the image in either the suppressed or dominant eye to determine whether the elicited P3b activity is probe or reversal related. We found that the timing of P3b (but not its amplitude) was closely related to the timing of the report of a perceptual change rather than to the onset of the probe. This is consistent with the proposal that P3b indexes updates in conscious awareness, rather than being related to stimulus processing per se. Conversely, the probe-related P1 amplitude (but not its latency) was associated with reversal latency, suggesting that the degree to which the probe is processed increases the likelihood of a fast perceptual reversal. Finally, the response-locked P3b amplitude (but not its latency) was associated with the duration of an intermediate stage between reversals in which parts of both percepts coexist (piecemeal period). Together, the data suggest that the P3b reflects an update in consciousness and that the intensity of that process (as indexed by P3b amplitude) predicts how immediate that update is.