High Quality Content by WIKIPEDIA articles! The flicker fusion threshold (or flicker fusion rate) is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the observer (this article centers on human observers). Flicker fusion threshold is related to persistence of vision. Although flicker can be detected for many waveforms representing time-variant fluctuations of intensity, it is conventionally, and most easily, studied in terms of sinusoidal modulation of intensity. There are then 6 parameters that determine the ability to detect the flicker: