INTERACTION OF STEREO VISION AND OPTIC FLOW PROCESSING REVEALED BY ANILLUSORY STIMULUS

The influence of stereoscopic vision on the perception of optic flow f ields was investigated in experiments based on a recently described il lusion, In this illusion, subjects perceive a shift of the center of a n expanding optic flow field when it is transparently superimposed by a unidirectional motion pattern, This illusory shift can be explained by the visual system taking the presented flow pattern as a certain se lf-motion flow field, Here we examined the dependence of the illusory transformation on differences in depth between the two superimposed mo tion patterns, Presenting them with different relative binocular dispa rities, we found a strong variation in the magnitude of the illusory s hift, Especially when translation was in front of expansion, a highly significant decrease of the illusory shift occurred, down to 25% of it s magnitude at zero disparity, These findings confirm the assumption t hat the motion pattern is interpreted as a self-motion flow field, In a further experiment we presented monocular depth cues by changing dot size and dot density, This caused a reduction of the illusory shift w hich is distinctly smaller than under stereoscopic presentation, We co nclude that the illusory optic flow transformation is modified by dept h information, especially by binocular disparity, The findings are lin ked to the phenomenon of induced motion and are related to neurophysio logy. (C) 1998 Elsevier Science Ltd.