Off-axis mesopic contrast sensitivity: The contribution of rods and cones from the interactions among SPD, luminance level and spatial frequency

Abstract

The basis of the human color vision across visual field demands more studies about the relative weights of cones and rods along the whole mesopic range. For studying the interaction of the SPD with luminance level, spatial frequency (fs) and age, we select two different SPDs of the stimulus/display in such a way that one of these has an important peak in 448nm. The used conditions were: a) CCT=3900K with S/P=1.79, and b) CCT=8600K with S/P=2.79. In this experiment took part 4 observers, (2 young and 2 older adults). We measured monocular CS for 1, 2 and 3 c/d under four photopic luminances (0.1, 0.3, 1 and 3 cd/m2) to an eccentricity of 10° in temporal area of the retina. The subject task was to discriminate the grating orientation of a single stimulus presentation with a 2AFC method, by pressing a button. Stimuli were presented in a TRC monitor controlled by a ViSaGe MKII Stimulus Generator from CRS. In meantime an eyetracker controlled the fixation. Results show: 1) For SP=1.79 mesopic CS increases with the luminance independently of spatial frequency and age, 2) The values of mesopic CS for 0.1cd/m2 much lower than those found for SP=2.79, 3) For S/P=2.79 for the two lowest values of luminances mesopic CS decreases as spatial frequency increases, while for the highest two luminances mesopic CS increases with spatial frequency. These results highlight the transition from dominance of the rods to cones and we also speculate about a contribution of the S cones for the high mesopic range that is evidenced in the growth of SC for the fs=3 c/d for both age groups.