Cyclopean stimuli

Cyclopean image is a single mental image of a scene created by the brain by combining two images received from the two eyes. The mental process behind construction of the Cyclopean image is crucial to stereo vision. Autostereograms take advantage of this process to trick the brain into forming an apparent Cyclopean image from seemingly random patterns.

Cyclopean image is named after the mythical Cyclops with a single eye. Literally it refers to the way stereo sighted viewers perceive the centre of their fused visual field as lying between the two physical eyes, as if seen by a cyclopean eye. Alternative terms for cyclopean eye include third central imaginary eye and binoculus.

The term cyclopean stimuli refers to a form of visual stimuli that is defined by binocular disparity alone. It was named after the one-eyed Cyclops of Homer’s Odyssey by Bela Julesz. Julesz was a Hungarian radar engineer. He thought that stereopsis might help to discover hidden objects, this might be useful to find camouflaged objects. The important aspect of this research was that Julesz showed using random dot stereograms (RDSs) that disparity is sufficient for stereopsis, where Charles Wheatstone had only shown that binocular disparity was necessary for stereopsis. Ironically, the Cyclops would not have been able to see a cyclopean stimulus, because having only one eye, he would not have been able to perceive binocular depth cues such as binocular disparity.

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