Abstract
The Pulfrich phenomenon is the visual illusory perception of motion-in-depth caused by a monocular reduction of luminance. Recently we showed that such illusion could also be caused after short-term monocular deprivation or “patching”, presumably caused by a monocular contrast-gain change. Therefore, to investigate this mechanism further, in this study we wanted to determine if it is possible to induce the Pulfrich phenomenon through contrast adaptation. We used a 3D passive screen using 3D glasses to adapt each eye to high contrast separately and display the Pulfrich stimulus. In each trial, participants were exposed to a 3-second-long contrast-adapting stimulus followed by structure-from-motion defined rotating cylinder made of Gabor patches. Adaptator contrast was 100% and stimulus contrast was either 100% or 15%. The differences between the right-eye-adapted and left-eye-adapted points of subjective equality (PSE) were then used to reveal the occurrence of the Pulfrich phenomenon. The results support the idea that adapting one eye to high contrast creates an interocular delay as the PSE values differed significantly after each eye adaptation. All the PSEs arising from left eye adaptation were significantly higher than those from right eye adaptation (p<0.001 for both 100% and 15% stimulus contrast), indicating a link of causation between which eye gets adapted and the direction of the phase shift. Furthermore, the gaps between the PSE values increased when reducing the contrast level of the Gabor patches from 100% to 15% (p<0.001). Contrast adaptation seems to influence the Pulfrich phenomenon through a unilateral increase in visual processing, creating an interocular delay. This finding hints at a key relationship between contrast gain control and the Pulfrich phenomenon.