Color stereopsis: a model for depth reversals based on border contrast.

Color stereopsis refers to the effect of stimulus color on perceived depth of stimuli viewed binocularly. It is well established and well understood that the wavelength of a stimulus affects its perceived depth in color stereopsis by prismatic effects in human optics, with long-wavelength stimuli normally seen in front of short-wavelength stimuli. It is less well known, and not well understood, that the background of the stimulus affects depth order as well. We demonstrate experimentally, using a long-wavelength orange stimulus and a short-wavelength blue stimulus, that a change from black to white in the background at the border (a change in border contrast) of the stimulus changes the perceived depth order from orange in front of blue to blue in front of orange (a color reversal). We present a descriptive model to explain reversals in color stereopsis when stimuli are displayed on a white background and suggest that it may account for instances of color reversals that are currently unexplained or questionably explained by other models.