Abstract
We investigated the influence of perceived depth on vergence eye movements while binocularly viewing a reverse perspective stimulus. In a reverse perspective stimulus, the perspective depth of a scene painted on a 3D surface strongly conflicts with the physical depth of the 3D surface. Subjects unfamiliar with the reverse perspective stimulus usually perceive the depth suggested by the perspective cue. Thus, of the two possible perceived depths, the one induced by the perspective cue is highly favored over the other one related to the physical dimensions of the 3D surface.
In an earlier experiment we did not find an influence of perceived surface slant polarity on vergence while viewing a bistable slant rivalry stimulus [ECVP 2006]. This negative result is not sufficient to conclude that such an influence does not exist, as the vergence changes related to the perceived slant may have been too small to be measurable. We hypothesize that as perceived depth is stable while viewing the reverse perspective stimulus, the influence of perceived depth on vergence ought to be stronger than in the bistable stimulus experiment.
We used a stimulus inspired by a 3D reverse perspective model of Wade and Hughes (“Cloudy Doors”, 1999). The stimulus (15×15 cm) was viewed at a distance of 55 cm. Vergence changes predicted by the physical dimensions of the surface were less than 1°. Vergence changes predicted by the perceived depth, however, ranged from 0° to about 6° in the opposite direction.
The results showed vergence changes of about 1° or less in directions predicted by the physical dimensions of the 3D surface. Thus, vergence changes in binocular viewing conditions corresponded better with the predictions based on the physical dimensions of the surface than with the predictions based on the perceived illusory depth.