Fig. 12. Dark adaptation curves following 13%, 24%, 42%, or 99% bleaches.37Solid lines show the percentage of pigment bleached. The Dowling-Rushton equation predicts that threshold should be proportional to the percentage of pigment bleached. The stimulus arrangement is shown in the inset in the upper panel. This holds for intense bleaches (bottom panel). However, bleaches below 7% are not well predicted by the equation. Psychophysical threshold is elevated dramatically by backgrounds that bleach only a small portion of the available pigment (top panel). (Rushton WAH, Powell DS: The early phase of dark adaptation. Vision Res 12:1083, 1972.)