Abstract

On a deep-red background the spectral sensitivity for 16-Hz flicker changes from M-cone to L-cone as the luminance approaches 5.5 log¹⁰ photopic td. The phase differences required to null middle-and long-wavelength flickering lights reveal that at frequencies below 16 Hz, M-cone flicker signals are delayed relative to L, but following an abrupt phase change of 180°, the reverse is the case at higher frequencies. These results suggest that at high light levels the usual rapid M-cone signal is combined with a slower one that has a relative phase lag of 180° near 16 Hz. On shorter wavelength backgrounds, qualitatively similar but smaller phases changes are found— as would be expected if the generation of the slow M-cone signal is not dependent on background color but is partly obscured by L-cone intrusion in the response to the middle-wavelength test light. In other conditions (for example, with less intense red background), phase differences are also found, but often with the opposite sign to those found on intense backgrounds.

© 1991 Optical Society of America