The multistable phenomenology includes (A) two face contours with three eyes (B and C) one dominant and one suppressed face and (D) a single central eye, as though of a cyclops.įor such a simple effect requiring only a mirror, it would be surprising if the third-eye rivalry effect had not been reported before. Maintaining Free Fusion of Both Pupils Concurrently in the Mirror Results in Third-Eye Rivalry. The ability to use one’s own face as a rivaling stimulus makes the current phenomenon a potentially useful stimulus in studying the dynamics of binocular rivalry, the neuroscience of consciousness, and the perception of one’s own appearance. From Figure 2, you can get a sense of the effect of third-eye fixation, assuming you have the ability to free fuse discordant signals after crossing your own eyes (for best results, find a mirror, or colleague, and stand as close as feasible, approximately 20–50 cm). The last percept is reminiscent of the one-eyed cyclops from Greek mythology. Phenomenologically, the observer tends to experience the following four percepts ( Figure 2): two transparent face contours with three eyes (Panel A), the intermittent alternation of face dominance and suppression (Panels B and C), with periods of percepts in which only a singular eye is visible (Panel D). The reflection of the subject in the mirror then becomes the object of perceptual rivalry. In third-eye rivalry, each eye concurrently fixates the opposing eye (or by uncrossing the eyes, each eye concurrently fixates itself), and the result is the clear and stable percept of a “third eye” in the midline of the stimulus. B: Normal fixation in a mirror involves binocularly viewing one pupil at a time, whereas third-eye rivalry (C) involves simultaneous fixation of both pupils, either through binocular convergence (as shown in red) or divergence (in blue).Īs has long been known in the binocular rivalry literature (see Alais & Blake, 2005 Wheatstone, 1838 for a review also Brascamp et al., 2015), discrepant monocular cues will be intermittently suppressed or dominant in awareness. The effect and procedure are depicted in Figure 1.Ī: A “third eye” results from free-fusing reflections of the left and right eyes in a mirror. The pupil of the “middle” eye will offer a strong enough vergence cue to help maintain stable fixation. If you then free fuse two of the reflected eyes, three will remain-two eyes will be perceived peripherally with a third eye seen between them. If you look in the mirror and cross (or uncross) your eyes, the usually singular percept of your own face staring back at you will be doubled, resulting in two adjacent faces with four eyes distributed horizontally. ![]() In the phenomenon reported here, we found that it is rather easy to use one’s own pupils as fixation targets. The effect is most easily achieved using a mirror to fixate each eye on its opposite. Here, we report a condition in which sustained free fusion results in vivid binocular rivalry from the reflection of one’s own face. The different interpretations can compete for perceptual dominance so that no percept persists indefinitely. When stable fixation is achieved, and if the brain receives conflicting information from each eye, the observer can experience a vivid sense of visual alternation (i.e., binocular rivalry). ![]() With effort, it is possible to change the vergence angle of the eyes and “free fuse” any two objects in the visual field in an attempt to see them as a singular object in depth. Three-dimensional vision is the result of binocular fusion, which occurs when each eye receives sufficiently similar information.
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