Conflict monitoring and attentional adjustment during binocular rivalry.

To make sense of ambiguous and, at times, fragmentary sensory input, the brain must rely on a process of active interpretation. At any given moment, only one of several possible perceptual representations prevails in our conscious experience. Our hypothesis is that the competition between alternative representations induces a pattern of neural activation resembling cognitive conflict, eventually leading to fluctuations between different perceptual outcomes in the case of steep competition. To test this hypothesis, we probed changes in perceptual awareness between competing images using binocular rivalry. We drew our predictions from the conflict monitoring theory, which holds that cognitive control is invoked by the detection of conflict during information processing. Our results show that fronto-medial theta oscillations (5-7 Hz), an established electroencephalography (EEG) marker of conflict, increases right before perceptual alternations and decreases thereafter, suggesting that conflict monitoring occurs during perceptual competition. Furthermore, to investigate conflict resolution via attentional engagement, we looked for a neural marker of perceptual switches as by parieto-occipital alpha oscillations (8-12 Hz). The power of parieto-occipital alpha displayed an inverse pattern to that of fronto-medial theta, reflecting periods of high interocular inhibition during stable perception, and low inhibition around moments of perceptual change. Our findings aim to elucidate the relationship between conflict monitoring mechanisms and perceptual awareness.

Sounds can boost the awareness of visual events through attention without cross-modal integration.

Cross-modal interactions can lead to enhancement of visual perception, even for visual events below awareness. However, the underlying mechanism is still unclear. Can purely bottom-up cross-modal integration break through the threshold of awareness? We used a binocular rivalry paradigm to measure perceptual switches after brief flashes or sounds which, sometimes, co-occurred. When flashes at the suppressed eye coincided with sounds, perceptual switches occurred the earliest. Yet, contrary to the hypothesis of cross-modal integration, this facilitation never surpassed the assumption of probability summation of independent sensory signals. A follow-up experiment replicated the same pattern of results using silent gaps embedded in continuous noise, instead of sounds. This manipulation should weaken putative sound-flash integration, although keep them salient as bottom-up attention cues. Additional results showed that spatial congruency between flashes and sounds did not determine the effectiveness of cross-modal facilitation, which was again not better than probability summation. Thus, the present findings fail to fully support the hypothesis of bottom-up cross-modal integration, above and beyond the independent contribution of two transient signals, as an account for cross-modal enhancement of visual events below level of awareness.