Binocular rivalry has been used to study a wide range of visual processes, from the integration of low-level features to the selection of signals that reach awareness. However, many of these studies do not distinguish between early and late phases of rivalry. There is clear evidence that the “onset” stage of rivalry is characterized by stable, yet idiosyncratic biases that are not evident in the average dominance of sustained rivalry viewing. Low-level stimulus features also have robust effects in the onset phase that are not seen in sustained rivalry, suggesting these phases may be driven at least partly by different neural mechanisms. The effects of high-level cognitive and affective factors at onset are less clear but also show differences from their effects in sustained viewing. These findings have important implications for the interpretation of any rivalry experiments using brief presentation paradigms and for understanding how the brain copes with binocular discrepancies in natural viewing conditions in which our eyes constantly move around an ever-changing environment. This review will summarize current research and explore the factors influencing this “onset” stage.

When an observer is presented with dissimilar images to the right and left eye, the images will alternate every few seconds in a phenomenon known as binocular rivalry. During sustained viewing, the timing of these switches appears to be unpredictable. Recent research has suggested that the initial ‘onset’ period of rivalry is not random and may be different in its neural mechanism than subsequent dominance periods. It is known that differences in luminance and contrast have a significant influence on the average dominance during sustained rivalry and that perception of luminance can vary between individuals and across the visual field. We therefore investigated whether perception of luminance contrast plays a role in onset rivalry. Observers viewed rival targets of equal brightness for brief presentations in eight locations of the near periphery and reported the color that was first dominant in each location. Results show that minimizing differences in brightness and contrast yields a stronger pattern of onset dominance bias and reveals evidence of monocular dominance. The results suggest that both contrast and monocular dominance play a role in onset dominance, though neither can fully explain the effect.

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When dissimilar images are presented to each eye, the images will alternate every few seconds in a phenomenon known as binocular rivalry. Recent research has found evidence of a bias towards one image at the initial ‘onset’ period of rivalry that varies across the peripheral visual field. To determine the role that visual field location plays in and around the fovea at onset, trained observers were presented small orthogonal achromatic grating patches at various locations across the central 3° of visual space for 1-s and 60-s intervals. Results reveal stronger bias at onset than during continuous rivalry, and evidence of temporal hemifield dominance across observers, however, the nature of the hemifield effects differed between individuals and interacted with overall eye dominance. Despite using small grating patches, a high proportion of mixed percept was still reported, with more mixed percept at onset along the vertical midline, in general, and in increasing proportions with eccentricity in the lateral hemifields. Results show that even within the foveal range, onset rivalry bias varies across visual space, and differs in degree and sensitivity to biases in average dominance over continuous viewing.