Nonstationarity in human perceptual ultradian rhythms.

Thirty subjects tests on the SAE for 8 hrs during morning and evening periods demonstrated significant ultradian rhythms in perception. The perceptual rhythms were nonstationary with respect to 1) the frequency of the rhythms reflected in some slowing of the rhythms during the course of the testing period, and in frequency differences between the morning and afternoon rhythms, and 2) the level of the illusion reflected in abrupt shifts in the magnitude of the SAE during the course of the testing period without subsequent recovery.