Abstract
Several studies have been manifested that local contour elements extracted by orientation selective cells in early visual areas are bound together by colinear connections in order to perceive global smooth curves (e.g., Field et al., 1993, Kapadia et al., 1995). In most studies investigating this contour integration, visual elements in each stimulus are on the same front-parallel plane. Therefore obtained results by these studies depict only 2D colinear connections for the contour integration mechanism. However, our visual experiences in daily life are binocular and we usually perceive 3D contours, so it is possible that the brain has 3D colinear connections for the contour integration.
A few studies used 3D stimuli with binocular disparity to investigate further characteristics of the integration mechanism (Hess & Field, 1995, Hess et al., 1997). Though each stimulus used by them contains patches with various depths, each patch is on a front-parallel plane. In order to investigate 3D integration mechanism in detail, it is necessary to use 3D contour elements oriented in depth.
This study executed psychological experiments using 3D contour stimuli with disparity gradient to address whether the 2D colinear connections clarified by previous studies are a subset of 3D colinear connections that integrate colinear elements fit on the smooth 3D curve.
3D versions of path-paradigm experiments are performed. Two types of contours that have the same global disparity gradient are used. One type of contours contain 3D colinear line element whose disparity gradients are the same as the one of the global contour, meanwhile the other type contain elements with reversed gradient, though their absolute value is the same as the of the global contour.
The results indicated that contours represented by colinear line element in 3D space are more salient than that of non-colinear elements. This suggests that colinear connections for the contour integration are organized in 3D manner.