TEMPORAL ASPECTS OF STEREOSCOPIC SLANT ESTIMATION - AN EVALUATION ANDEXTENSION OF HOWARD AND KANEKOS THEORY

We investigated temporal aspects of stereoscopically perceived slant p roduced by the following transformations: horizontal scale, horizontal shear, vertical scale, vertical shear, divergence and rotation, betwe en the half-images of a stereogram. Six subjects viewed large field st imuli (70 degrees diameter) both in the presence and in the absence of a visual reference. The presentation duration was: 0.1; 0.4, 1.6, 6.4 or 25.6 s. Without reference we found the following: rotation and div ergence evoked considerable perceived slant in a number of subjects. T his finding violates the recently published results of Howard and Kane ko, Slant evoked by vertical scale and shear was similar to slant evok ed by horizontal scale and shear but was generally less. With referenc e we found the following: vertical scale and vertical shear did not ev oke slant. Slant due to relation and divergence was similar to slant d ue to horizontal scale and shear but was generally less. According to the theory of Howard and Kaneko, perceived slant depends on the differ ence between horizontal and vertical scale and shear disparities. We m ade their theory more explicit by translating their proposals into lin ear mathematical expressions that contain weighting factors that allow for both slant evoked by rotation or divergence, subject-dependent un derestimation of slant and other related phenomena reported in the lit erature. our data for all stimulus durations and for all subjects is e xplained by this 'unequal-weighting' extension of Howard and Kaneko's theory. (C) 1998 Elsevier Science Ltd. All rights reserved.