Binocular fusion of luminance, color, motion and flicker--two eyes are worse than one.

UNLABELLED: How much information is conserved, or discarded, as it travels through the visual system? A target (an oriented bar) was defined by dark grey spots embedded in light spots for the left eye, and by light grey spots embedded in dark spots for the right eye. With one eye open, the target bars were clearly visible, but with both eyes open the light and dark spots fused binocularly into medium grey and the target vanished. Results were similar for color; the target comprised greenish spots embedded in reddish spots for the left eye, and by reddish spots embedded in greenish spots for the right eye (somewhat like an Isihara color plate). RESULT: The colored targets were invisible when both eyes were open but reappeared when one eye was closed. Small targets that moved in opposite directions in the two eyes were visible to each eye alone by common fate, but motion averaging made them disappear when both eyes were open. CONCLUSION: Opposed retinal luminances or colors were averaged out by binocular fusion, but could be retrieved by a special afterimage technique in Experiment 6. Conversely, in Experiment 7 dichoptic target spots flickered in counterphase but background spots flickered in-phase to the two eyes. RESULT: The targets were invisible monocularly but became visible as reduced-flicker when fused binocularly. We conclude that two eyes were worse than one eye when opposite colors or movements were fused (Experiments 1-6) but were better than one when binocular correlations could be extracted (Experiment 7). These experiments show how much of the visual information gets transmitted, gets discarded, can still be retrieved, or reaches conscious awareness.