Traveling waves of activity in V1 correlate with perceptual dominance during binocular rivalry

Background: When the two eyes view large dissimilar patterns, alternating waves of visibility are experienced, as one pattern sweeps the other out of awareness. As shown by Wilson et al (2001), the dynamics of these waves coincide with the functional architecture of early visual cortex: retinotopic organization, cortical magnification and collinear facilitation. This coincidence suggests that V1 is a possible site of the neural events promoting perceptual waves. Methods: Observers dichoptically viewed a low-contrast radial annulus and a high-contrast spiral annulus, each 4 in radius and .72 in width, while fMRI signals were measured in a 3T scanner. Each 9-sec trial started with the low-contrast annulus presented to one eye, which was followed immediately by the high-contrast annulus to the other eye. This mode of presentation promoted complete suppression of the low-contrast annulus at the beginning of every trial. Shortly thereafter, a brief contrast increment appeared in a narrow region at the top of the suppressed annulus. This contrast increment usually triggered dominance of that region of the annulus, with this dominance then spreading such that the low-contrast annulus progressively erased the high-contrast annulus from awareness, over a period of 1.5 - 3 s. When the wave reached the bottom of the annulus, observers pressed a key, which caused the entire display to disappear, then classified dominance waves based on their direction and quality: 'left hemifield', 'right hemifield' or 'no' wave. Results: In V1, temporal phases of fMRI signals varied orderly across the retinotopic map: signal fluctuations were more delayed in more dorsal portions of this map. Furthermore, the differences in phase were correlated with the latency, direction and quality of waves reported by observers. Conclusion: The fine-scale analysis of fMRI signals reveals a tight link between spatiotemporal dynamics of dominance waves during rivalry and concomitant neural events in V1.