Present two incompatible images simultaneously — one to each eye — and the brain cannot fuse them. Instead of averaging or overlapping them, it suppresses one completely and perceives the other. After a few seconds, it switches. The physical input never changes. Only the conscious percept does.
This makes rivalry one of the cleanest experimental windows into consciousness: the stimulus is held constant while subjective experience varies, isolating what the brain does when it decides what to perceive.
Every theory of consciousness must answer a question rivalry makes unavoidable: what decides which percept wins? Materialist answers — stochastic neural competition, GABAergic inhibition cycling, attractor dynamics — displace agency entirely. Dualist answers relocate it to a quasi-transcendent level.
Nobel laureate John Eccles argued the rivalry-switcher would be a soul-mediated event. Penrose and Hameroff's Orch-OR theory (2025) is the first to directly cite rivalry timing as evidence for a non-computational observer. Dennett's counter — the "Cartesian Theater" — argues there is no central stage and no inner audience: the switching is the experience, with nothing further to explain.
The most interesting question to carry into the experiment: does it feel like you are switching? Or like something is switching on you?
Ketamine is an NMDA receptor antagonist. Its primary target is GABAergic interneurons — the cells that drive the V1 rivalry oscillator through reciprocal inhibition. Blocking them should slow or destabilize spontaneous switching, prolong mixed states where both images coexist, and weaken voluntary control of which percept dominates.
Separately, ketamine inhibits the mitochondrial TCA cycle, triggering adenosine surges in the medial prefrontal cortex. This is the mechanism underlying its rapid antidepressant effects — and it disrupts the same frontoparietal circuits that mediate conscious access and self-reporting. The dissociation specifically severs the sense of being a unified witness from the perceptual stream.
Run each experiment sober first to establish a baseline. The ratio of sober to altered-state results — especially the MAE Timer — is a direct personal measure.
Rivalry experiments require cross-eye fusion: look at the two dots above the canvases and cross your eyes gently until they become three. Focus on the middle image. No equipment needed. Alternatively, toggle ANAGLYPH and use red-cyan glasses.
Solo experiments require only fixation: stare at the centre cross without moving your eyes. The effect builds with time.
MAE Timer: press INDUCE, stare at the spiral for 30 seconds, then watch how long the static face appears to move. Record your sober time. Compare later.
Press ▶ HEAR INSTRUCTIONS at any time for spoken guidance through the current experiment.