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Michael Silver, Nikos Logothetis; Temporal frequency and contrast tagging bias the type of competition in interocular switch rivalry. Journal of Vision 2007;7(9):58. doi: 10.1167/7.9.58.
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The nature of competition underlying perceptual alternations in binocular rivalry remains controversial. Interocular switching (IOS) of orthogonal gratings at a rate of 3 Hz can result in slow irregular perceptual alternations that persist over multiple stimulus switches (Logothetis et al., 1996). That is, subjects experience periods of perception of a particular orientation and phenomenal suppression of the other orientation, even though both orientations are presented to both eyes during each of these periods of stable perception. This result argues against competition based on eye-of-origin signals for IOS rivalry and is more consistent with competition between stimulus representations. However, changes to low-level stimulus features such as contrast, spatial frequency, and/or interocular switch rates in IOS rivalry can generate a different percept in which the perceived orientation changes with every stimulus switch (Lee and Blake, 1999). Because this fast regular alternation is identical to the stimulus sequence presented to a single eye, the underlying competition has been postulated to be between the two monocular pathways. We have employed temporal frequency and contrast tagging to label either eye-of-origin or stimulus orientation in IOS rivalry between orthogonal gratings. The relative amounts of fast regular and slow irregular perceptual alternations were measured for human observers using a subjective rating scale. Tagging of eye-of-origin enhanced fast regular alternations (characteristic of eye rivalry), while orientation tagging enhanced slow irregular alternations (characteristic of stimulus rivalry). These results suggest that when the visual system is presented with two different perceptual ambiguities (interocular and orientation incompatibility), additional information in the stimuli biases the type of perceptual alternation. The results are consistent with a model in which the brain combines information across multiple visual features to resolve ambiguities in visual inputs.
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