Abstract

Detection of temporally modulated light is linear at high temporal frequencies; near critical flicker frequency (CFF), threshold is determined by the absolute amplitude of the modulation, independent of the luminance or the Weber ratio associated with the stimulus. We measured CFF at 555 nm and 660 nm over a 5-log unit range of intensities. The resulting CFF/logintensity functions were linear, obeying the Ferry-Porter law over the entire range. However, the slope for 555-nm light was significantly steeper, by as much as 17% in the foveola and 25% at 35° eccentricity. If the R- and G-cone pathways had identical temporal properties, and if detection were based on the most sensitive mechanism, the 555-nm and 660-nm CFF/log/ functions would necessarily have identical slopes; however, the signals from the two cone types were combined. This implies that the G-cone pathway has a faster linear temporal response that the R-cone pathway, invalidating the assumptions of heterochromatic flicker photometry. At high intensities, the differing temporal properties of the two cone pathways can lead to more than a log unit mismatch in luminance for a pair of stimuli that appeared matched at low a intensity. A new, threshold based definition of luminance is proposed.

© 1991 Optical Society of America