Abstract

We have recently shown¹ that for gratings of constant relative size the increase of contrast sensitivity with luminance obeys a single saturating function of stimulus flux irrespective of spatial frequency (<4 c/deg) or grating area. Relative grating size (Z) is expressed in square cycles and is calculated by multi plying grating area (A) by spatial frequency (f) squared. Flux (F) is expressed in phot, td deg² and is calculated by multiplying retinal illuminance by grating area. We measured contrast sensitivity as a function of retinal illuminance using gratings of various areas at each spatial frequency. Contrast sensitivity was found to increase with relative grating area and stimulus flux similarly at all spatial frequencies. The experimental data was described by Eq. (1): S = S_max (1 + Z_c/Z)^-0.5 [1 + (F_c/F)^0.5]^-1, where contrast sensitivity (S) is the dependent variable, relative grating size (Z) and flux (F) are the independent variables, and the maximum contrast sensitivity (S_max), critical number of square cycles (Z_c), and critical flux (F_c) are the parameters of Eq. (1). The equation combines the Pipers, DeVries-Rose, and Weber laws to a single law.

© 1992 Optical Society of America