Abstract
Introducing differences to the left-eye and right-eye images is an informative way to study stereoscopic depth perception, and particularly relevant to optically-limited stereoscopic displays (e.g., virtual and augmented reality). One such example with dynamic visual inputs is the Pulfrich effect–a depth misperception observed for horizontally moving objects with interocular luminance differences classically applied globally to both the moving stimuli and their background. Here, we disentangled the effects of the interocular luminance differences of moving stimuli and background in the Pulfrich effect. In our experiment, an observer judged the perceived direction of the 3D rotation of a sinusoidally-moving pair of small white squares presented against a gray background. The stimuli were presented in a mirror haploscope. In randomly interleaved trials we applied interocular luminance differences to the moving stimulus, the stationary background, or both. The stimulus and background manipulations introduced interocular contrast differences, which are also known to cause the Pulfrich effect. To estimate the magnitude of the illusory depth percept, we introduced a nulling interocular delay to the undimmed eye, and measured psychometric functions using the method of constant stimuli. Surprisingly, we found that the interocular delay required to null the effect was larger with the stimulus-only luminance manipulation than with the classic global or the background manipulation. Our results suggest that contrast plays a more significant role in modulating the phenomenon than previously thought. However, the source of the contrast variation (object versus background luminance) is important; larger effects were seen when the target luminance was varied than vice versa. These results have potentially important implications for understanding neural mechanisms responsible for this spatio-temporal illusion.