Long-distance interactions in Cyclopean vision.

We report on evidence for selective long-distance interactions in Cyclopean binocular vision. When presented with a pair of Cyclopean test bars observers could discriminate trial-to-trial uncorrelated variations in the mean orientation, orientation difference, separation and mean location of the test bars while ignoring random variations in the orientation, width and location of a third bar placed between the two test bars. We propose that the human visual system contains Cyclopean long-distance comparators (i) that compare the outputs of two narrow receptive fields some distance apart while being insensitive to stimuli located between those receptive fields, and (ii) the outputs of which carry orthogonally labelled indicators of orientation difference, mean orientation, separation and mean location. In the evolutionary context, one role for the proposed mechanisms might be to encode information about the silhouettes of animals whose camouflage is broken by the binocular vision of predators.