Spatial frequency tuned covariance channels for red-green and luminance-modulated gratings: psychophysical data from human infants.

This study concerns the spatial-frequency-tuned channels underlying infants' contrast sensitivity functions (CSFs) for red-green chromatic stimuli, and their relationship to the channels underlying infants' CSFs for luminance-modulated stimuli. Behavioral (forced-choice preferential-looking) techniques and stationary stimuli were used. In experiment 1. contrast thresholds were measured in 4- and 6-month-olds, using isoluminant red-green gratings with spatial frequencies ranging from 0.27 to 1.53 c deg. In experiment 2. contrast thresholds were measured in 4-month-olds. using both red-green and luminance-modulated gratings in the same low spatial frequency range. Covariance analyses of individual differences were performed. Experiment 1 revealed one dominant covariance channel for the detection of red-green gratings, with a second channel contributing to detection of the highest spatial frequencies used. Experiment 2 revealed two to three channels serving color and luminance: but surprisingly these channels were not statistically separable for luminance versus chromatic stimuli. Thus, covariance channels for color and luminance that are independent for adults [Peterzell & Teller (2000). Spatial frequency tuned covariance channels for red-green and luminance-modulated gratings: psychophysical data from human adults. Vision Research, 40, 417-430] are apparently interdependent in infants. These data suggest that for infants, detection thresholds for chromatic and luminance-modulated stimuli may be limited by common mechanisms.