Abstract
In binocular rivalry, conflicting images presented to the two eyes result in a visual percept that alternates between the two images, even though the visual stimuli remain constant. By dissociating visual stimulus from conscious percept, the study of binocular rivalry can shed light on the neural selection processes that lead to awareness. These selection processes have been shown to occur at multiple levels in the visual processing hierarchy, but the factors that determine the level at which perceptual selection is resolved are not well understood. Interocular switch (IOS) rivalry is a special form of binocular rivalry in which two conflicting images are swapped between the two eyes about three times per second. IOS rivalry elicits two types of percepts: eye rivalry, in which perceptual selection operates on monocular representations, and stimulus rivalry, which requires integration of information from both eyes over time and is thought to occur at a higher level in the visual processing hierarchy. We varied the spatial and temporal frequency of orthogonal gratings in IOS rivalry and measured the proportions of eye and stimulus rivalry. High spatial frequencies were preferentially associated with stimulus rivalry, and for low spatial frequency gratings, higher temporal frequencies promoted eye rivalry. This pattern correlates with the temporal and spatial frequency selectivities of the magno- and parvocellular visual streams. Specifically, it suggests that the magno stream is important for eye rivalry, while the parvo stream is associated with stimulus rivalry. We tested this hypothesis directly by using red/green isoluminant stimuli to reduce the activity of the magno stream and found that isoluminance increased the amount of stimulus rivalry, as predicted by the magno/parvo framework. This framework accounts for a number of stimulus dependencies reported in the IOS rivalry literature and suggests that the magno- and parvocellular pathways have distinct roles in perceptual selection.
National Science Foundation Graduate Research Fellowship.