Consciousness: Confessions of a Romantic Reductionist (The MIT Press)

by Christof Koch

Binocular rivalry is another one. In binocular rivalry, a small picture, say of a face, is shown to your left eye, and another photo, say the old imperial flag of Japan (with its rays of light emanating from a central disk) to your right eye. You might think that you see the face superimposed onto the flag. If the illusion is set up correctly, though, you will perceive the face alternating with the flag. Your brain won’t let you see two things at the same time in the same place. At first, you vividly see the face without a hint of the sunburst pattern; after a couple of seconds, a patch of the flag appears somewhere in your field of view, erasing the underlying facial pattern at that location. From this initial seed, the image spreads until the face is entirely gone and only the flag remains. Then the eyes start to shine through. The patchwork of flag–face image resolves itself a few seconds later into a whole face. Then the percept of the flag establishes dominance again. And on and on. The two images move in and out of consciousness in a never-ending dance. You can abort this dance by closing one eye—you’ll instantly resolve all ambiguity and perceive the image present to the open eye.