Ultradian rhythms in the perception of the spiral aftereffect

Young adults were tested on the spiral aftereffect (SAE) for 8-h periods during the day and night. Using time series analyses, prominent cyclicity components in the perception of the illusion were revealed, with periodicities of the SAE the same order of magnitude as the REM-nonREM cycle. It appeared that the duration of the SAE could be used as a sensitive behavioral index of the basic rest-activity cycle.