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.
Rhythmic visual stimuli can entrain ongoing neural oscillations in the human brain, locking the timing of excitability cycles and enhancing processing of predictable stimuli. The study shows that the phase of existing brain oscillations can be modified by rhythmic visual stimulation in the alpha frequency band, leading to phase-locked fluctuations in excitability that produce concomitant fluctuations in visual awareness. This entrainment effect depended on the amount of spontaneous alpha power before the experiment and the level of 12-Hz oscillation before each trial, and could not be explained by evoked activity. The findings support a role for alpha oscillations as pulsed inhibition of cortical activity and provide evidence for the quantized nature of conscious experience.