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Foundations of Cyclopean Perception

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Imagine yourself walking through a field of tall grass with one eye shut. Right ahead of you is a striped animal, a zebra say, that is invisible, perfectly blended with the grassy background. Now open both eyes. Suddenly, the zebra appears before you, its contours revealed in depth. Information about the zebra's shape was not present in the patterns of light that went into each of your eyes but the information is there in the difference between the patterns.
To create this effect artificially it is necessary to be able to generate and manipulate complex patterns of light and dark elements that model the highlights and shadows that fell on your eyes in that sunny field. It was Bela Julesz who recognized that computer technology made this possible. He called the stimuli that produce this effect 'random dot stereograms' and the process through which the effect works 'cyclopean perception'. Julesz also realized that the effect could be exploited to gain insights into the information processing that goes on in visual perception.
Julesz was inspired by an idea of Seymour Papert's to devise a methodology that he called 'psychoanatomy.' The idea is that information that goes into the eyes is extracted in stages. But, in general, the system the mediates between the eye and our
conscious knowledge of what we see is a black box; We can't tell in what order the information is analyzed. With a random dot stereogram, however, it is possible to distinguish between information that is available to the individual eyes and information that only becomes available once images from the two eyes are synthesized. One can infer that the first kind of information must be extracted early in the visual process, before the inputs from the two eyes come together while information of the second kind must be extracted later, at or after, the stage when the inputs come together.
Julesz explains all this very clearly and throws out many other ideas as well, including an interesting model of the physiology of stereo perception. The book is also a visual treat, full of striking stereograms.