Very-long-term chromatic adaptation and short-term chromatic adaptation: Are their influences cumulative?

Do very-long-term (VLT) and short-term chromatic adaptation have a cumulative influence on color vision? VLT adaptation results from exposure to an altered chromatic environment experienced over days or weeks. Color shifts from VLT adaptation are measured hours or days after leaving the altered environment. Short-term adaptation results from exposure for a few minutes or less, with color shifts measured within a few seconds or minutes after the adapting light is extinguished. Here, both types of adaptation were combined. Shifts in unique yellow caused by short-term chromatic adaptation can be ∼10 times greater than for VLT adaptation. The specific question considered here is whether the color shift from VLT adaptation is cumulative with the far larger shift from short-term adaptation or, instead, does much stronger short-term adaptation eliminate the modest color shifts caused by VLT adaptation? All adaptation was to reddish-appearing long-wavelength light; shifts in unique yellow were measured. For VLT adaptation, the subject viewed for one hour daily a CRT monitor that displayed a moving red grating (Judd x = 0.60, y = 0.35, 22.4 cd/m2). Adaptation was repeated daily for 12 to 14 days. Unique yellow was measured before the start of each day's VLT adaptation, i.e., 22+ hours after the end of VLT adaptation on the previous day. The subject set an admixture of 540nm-plus-660nm light to appear equilibrium yellow at five luminance levels between 0.5 and 2.5 log trolands. For short-term adaptation, exposure to a 660 nm adapting light at 100 td was incorporated into the testing session for equilibrium yellow measurements. Shifts in unique yellow due to only short-term or to only VLT adaptation also were measured. The color shifts from VLT and short-term adaptation were cumulative, which is consistent with short-term and VLT chromatic adaptation acting independently.