Figure 7.
Mean matching luminance (collapsed across all observers) is plotted against mean ODOG model output for all 45 regions of interest in the stimuli of Experiments 1 and 2. Circular symbols plot data from staircase stimuli: red, green and blue refer to steps on the 5, 62, and 119 cd/m2 backgrounds, and bright and dark colors denote the sequential and disrupted staircase conditions, respectively. Square symbols plot data from simultaneous brightness/lightness contrast stimuli: black, gray and white refer to the 24, 60, and 100 cd/m2 test patches, respectively. In panel (a) the data are fit to a linear function possessing two free parameters (K=2): a y-intercept and a slope. The fitted y-intercept is 63.9 cd/m2, and the slope is 0.268 cd/m2 per unit model output. The correlation is highly significant, r(44)=0.93, p<.0001, and accounts for over 86% of the total variance. In panel (b) mean stimulus luminances are introduced as a priori y-intercepts, and the data were fit to a system of three linear functions with just a single free parameter (K=1): the slope. The value of the fitted slope parameter is 0.309 cd/m2 per unit model output. The correlation of matching luminance and ODOG model output is again highly significant, r(44)=0.98, p<.0001, and accounts for 97% of the total variance in matching luminance.