Meaning of gamma distribution in perceptual rivalry

Perceptual rivalry, which implies binocular rivalry and ambiguous figure perception, is characterized by perceptual alternation between two stable interpretations of an unchanging stimulus. It is well known that the time intervals of alternation follow a gamma distribution (GD) commonly in various kinds of perceptual rivalry. A critical question is whether the GD reflects some general mechanism of this phenomenon. In quantitative investigations of distributions of the alternation intervals, we found that a shapedetermining parameter α of GD took a natural number, indicating that the alternation is caused by a discrete stochastic process of the brain. In an extended version of the same experiment, we confirmed that the same property was obtained for each of the various kinds of stimuli. Therefore it is concluded that the GD reflects the general mechanism of perceptual rivalry, that is, the discrete stochastic process underlying perceptual alternation.