What covariance mechanisms underlie green/red equiluminance, luminance contrast sensitivity and chromatic (green/red) contrast sensitivity?

In order to investigate the mechanisms underlying green/red equiluminance m atches in human observers and their relationship to mechanisms subserving l uminance and/or chromatic (green/red) contrast sensitivity, we tested 21 hu man subjects along these dimensions at 16 different spatial and temporal fr equencies (spatial frequency, 0.25-2 c/deg; temporal frequency, 2-16 Hz) an d applied factor analysis to extract mechanisms underlying the data set. Th e results from our factor analysis revealed separate sources of variability for green/red equiluminance, luminance sensitivity and chromatic sensitivi ty, thus suggesting separate mechanisms underlying each of the three main c onditions. When factor analysis was applied separately to green/red equilum inance data, two temporally-tuned factors were revealed (factor 1, 2-4 Hz; factor 2, 8-16 Hz), suggesting the existence of separate mechanisms underly ing equiluminance settings at low versus high temporal frequencies. In addi tion, although the three main conditions remained separate in our factor an alysis of the entire data set, our correlation matrix nonetheless revealed systematic correlations between equiluminance settings and luminance sensit ivity at high temporal frequencies, and between equiluminance settings and chromatic sensitivity at low temporal frequencies. Taken together, these da ta suggest that the high temporal frequency factor underlying green/red equ iluminance is governed predominantly by luminance mechanisms, while the low temporal frequency factor receives contribution from chromatic mechanisms. (C) 2000 Elsevier Science Ltd. All rights reserved.