INDIVIDUAL-DIFFERENCES IN CONTRAST SENSITIVITY FUNCTIONS - THE LOWESTSPATIAL-FREQUENCY CHANNELS

The number and nature of spatial channels tuned to low spatial frequen cies in photopic vision was examined by measuring individual differenc es in the contrast sensitivity functions (CSFs) of seven visually norm al adults. Stationary, 51 cd/m(2), low spatial frequency sinusoidal gr atings between 0.27 and 2.16 c/deg were used as stimuli. Correlational and factor analyses revealed that the set of CSFs contained only one statistical source of individual variability at spatial frequencies be low 1 c/deg (tuned to a peak of about 0.8 c/deg), and a second source above 1 c/deg (tuned to about 1.4 c/deg). The sources (''factor-channe ls'') mapped well onto the two coarsest spatial frequency channels fro m some existing computational models. The analysis was applied also to earlier data from 4-, 6- and 8-month-old infants, in which two source s of variability have been found below 1 c/deg [Peterzell, D. H., Wern er, J. S. & Kaplan, P. S. (1995). Vision Research, 35, 961-980]. The c ombined results are consistent with the hypothesis that in photopic vi sion of the neonate, there are two channels with peak sensitivities be low 1 c/deg, and that these channels shift their tuning from lower to higher spatial frequencies by about a factor of four during developmen t. Copyright (C) 1996 Elsevier Science Ltd.