Fig. 4.

JMH's results from discrimination and matching experiments for LM tests and backgrounds that varied in their LM input. The top six panels are discrimination thresholds (JNDs) plotted as a function of pedestal intensity. The three left panels are JNDs for decrements and the three right panels are JNDs for increments presented on, from top to bottom, the Gray+LM, Gray and Gray−LM backgrounds. Error bars are 95% confidence intervals. The bottom panel shows asymmetric matching data for the same set of conditions. The x axis is the test excursion (i.e., the number of isomerizations expected from the test independent of the background) against the Gray+LM (circles) and the Gray−LM (triangles) backgrounds. The y axis is the match excursion from the gray background against which the matches were set. Error bars are standard error of the mean. Dashed and solid lines are results of model fits with parameters selected on the basis of both discrimination and matching data. These are fits for the gain-and-subtractive model of adaptation. Increments and decrements were fit independently but the p,q, and M parameters in Eq. (2) were yoked across adapting conditions. The raw psychometric and matching data underlying the points and model fits shown in this figure and Figs. 4-7 can be obtained at http://color.psych.upenn.edu/supplements/com_uniform/.