Abstract

When the number of ganglion cells stimulated at various retinal locations are kept constant by M-scaling deep-red targets on deep red backgrounds, then log CFF = 0.19 log F + 1.3, where F is luminous flux collected by ganglion-cell receptive-field centers and is calculated by multiplying photopic retinal illuminance by Ricco's area at each eccentricity. Thus, the Ferry–Porter law for red stimuli can be generalized across the visual field by replacing stimulus luminance by F (cf.¹). Although red targets stimulated predominantly cones, rod intrusion was possible. Therefore, in the present study we measured CFF to red targets on yellow backgrounds as a function of eccentricity and retinal illuminance. Temporal modulation visible to cones was 30%. However, scotopic temporal modulation was only 1%, which is never visible to rods.² We found that log CFF = 0.27 log F + 1.1 (r² = 0.95). The slope is steeper than in our earlier study (see above) because as retinal illuminance decreased CFF to red targets on yellow backgrounds became progressively lower than CFF to red targets on red backgrounds. Thus, the contribution of rods to CFF increases with decreasing retinal illuminance, even for deep-red targets and backgrounds. Moreover, the Ferry–Porter law can be generalized across the visual field, even when flicker is made invisible to rods by using red targets on yellow backgrounds.

© 1990 Optical Society of America