Fig. 5. Effects of chromatic adaptation on visual thresholds in the rat. Increment thresholds for two test lights (510nm and 390nm) were measured on 560nm backgrounds of various intensities. Each plotted point is a comparison of the elevation in threshold produced for the two test wavelengths at a single background light intensity. Results are shown for three subjects. The straight line is the best-fitting linear regression (slope=0.71, r²=0.93, P<0.001). The broken line shows the relationship between the threshold elevations for the two test wavelengths expected if the two cone mechanisms had adapted univariantly.