Abstract
When binocular disparities define a transparent cylinder to rotate clockwise while Pulfrich Effect (PE) does the same cylinder to rotate anticlockwise, what would be the perceived depth and direction of the cylinder? We examined the properties of interaction between disparities and PE. For this purpose, we constructed a dynamic random dot stereogram that simulated a transparent cylinder rotating clockwise. When the stereogram was viewed through a stereoscope with ND filter on the observer's right eye, PE provided information for anticlockwise rotation while disparities did for clockwise rotation. Magnitudes of disparities and intensity of ND filter were manipulated. Observers reported the perceived depth and rotation direction of the cylinder under four different conditions: disparities only /PE only conditions where the rotation direction of the cylinder was defined only by disparities or only by PE and consistent/inconsistent conditions where both disparities and PE defined consistent/inconsistent rotation direction of the cylinder. The perceived depth of the cylinder in the consistent condition was larger than that under each disparities only and PE only condition but smaller than the sum of the perceived depth under each condition. The perceived depth of the cylinder in the inconsistent condition was smaller than that under the consistent condition; however, interestingly, it was sometimes bigger than that under the disparities only or PE only condition. The perceived rotation direction of the cylinder in the inconsistent condition depended on the magnitudes of disparities and the intensity of ND filter. Surprisingly, multiple regression analysis shows that PE appears to be a more important contributor than disparities in the perception of depth and rotation direction. These results imply that there exists a mechanism affected by both disparities and PE and that this mechanism does not linearly summate both inputs from disparities and PE.
This work was supported by Korea Research Foundation Grant (KRF-2002-074-HS1003)