Abstract
Any processing delay between the two eyes can result in illusory 3D percepts for moving objects because of either changes in the pure disparities over time for disparity sensors or by changes to sensors that encode motion/disparity conjointly. This is demonstrated by viewing a fronto-parallel pendulum through a neutral density (ND) filter placed over one eye, resulting in the illusory 3D percept of the pendulum following an elliptical orbit in depth, the so-called Pulfrich phenomenon. Here we use a paradigm where a cylinder rotating in depth, defined by moving Gabor patches is presented at different interocular phases, generating strong to ambiguous depth percepts. This paradigm allows one to manipulate independently the contrast and the luminance of the patches to determine their influence on perceived motion-in-depth. Thus we show psychophysically that an interocular contrast difference can itself result in a similar illusory 3D percept of motion-in-depth. We argue that contrast, like luminance (ND filter) can modify the dynamics of visual neurons resulting in an interocular processing delay or an interocular velocity difference.
Highlights
Any processing delay between the two eyes can result in illusory 3D percepts for moving objects because of either changes in the pure disparities over time for disparity sensors[1] or by changes to sensors that encode motion/ disparity conjointly[2]
In human and non-human primates, binocular neurons in MT, encoding motion-in-depth are sensitive to disparity, interocular velocity differences and delays[9,10,11,12,13,14,15], similar to that generated by a monocular luminance decrement, suggesting that the delay induced by a luminance decrement is responsible for the perception of illusory motion-in-depth in the Pulfrich phenomenon[16, 17]
One can see that the psychometric function is shifted to the left when the luminance is decreased over the left eye which means that the cylinder is seen more often rotating clockwise; and that it is shifted to the right when the luminance is decreased over the right eye, meaning that the rotation is seen more anticlockwise
Summary
Any processing delay between the two eyes can result in illusory 3D percepts for moving objects because of either changes in the pure disparities over time for disparity sensors[1] or by changes to sensors that encode motion/ disparity conjointly[2]. The low-level interocular phase manipulation creates an actual disparity This paradigm involves structure-from-motion and depth perception mechanisms[12] and allows one to manipulate independently the contrast and the luminance of the patches. This allows for the precise measurement of the interocular delay in terms of the phase difference between the two eyes’ images at the point of subjective equality (PSE) where the cylinder’s clockwise and anticlockwise rotation is ambiguous. The subjects’ task was to report whether they saw the cylinder rotating clockwise www.nature.com/scientificreports/
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