Binocular rivalry requires visual attention.

An interocular conflict arises when different images are presented to each eye at the same spatial location. The visual system resolves this conflict through binocular rivalry: observers consciously perceive spontaneous alternations between the two images. Visual attention is generally important for resolving competition between neural representations. However, given the seemingly spontaneous and automatic nature of binocular rivalry, the role of attention in resolving interocular competition remains unclear. Here we test whether visual attention is necessary to produce rivalry. Using an EEG frequency-tagging method to track cortical representations of the conflicting images, we show that when attention was diverted away, rivalry stopped. The EEG data further suggested that the neural representations of the dichoptic images combined without attention. Thus, attention is necessary for dichoptic images to be engaged in sustained rivalry and may be generally required for resolving conflicting, potentially ambiguous input and giving a single interpretation access to consciousness.