Two types of experiments are reviewed that measure the separate (unconscious) perceptual strengths of images processed by each eye while the observer perceives only a combined, single cyclopean image. The first experiment deals with an enigma: when the two eyes view identical high-contrast stimuli and then one eye closes, perceptually, nothing seems to change. Does this mean that only one eye's stimulus was used for the cyclopean perception? In fact, when the two eyes receive similar stimuli but possibly of different contrasts, both stimuli contribute to the cyclopean image approximately in proportion to a power, typically about 2, of their overall contrast (Ding and Sperling, PNAS, 2006). The authors demonstrate a neural competition mechanism that accounts for both the power law and the enigma. The second group of experiments (Bartels and Logothetis, JOV, 2010) explores the time course of binocular rivalry in which very different images are presented to the two eyes and only one is perceived. A re-analysis of their data enables measurement of the relative strengths of the two components of perceptual image strength, one relatedto the eye receiving the image and the other to the nature of the imageitself. Both components decline in strength linearly and in parallel as a function of time since stimulus onset.
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