Critical flicker frequency and centrally-acting drugs.

THE critical flicker frequency (cff) may be defined as the fastest rate at which a flickering source of light appears to be flickering as opposed to being steady. It has a number of determinants including the luminance, wave-length, wave-form, and light-dark ratio of the stimulating light, the area, position, and light-adapted state of the retina illuminated, the duration of exposure, and the size of the pupil. Age and constitutional factors may also influence the threshold, and recently the importance of intersensory effects and previous adaptation to intermittent light have been emphasized (Turner 1965a, b).