Abstract
A striking illusion of the color propagation, termed “Neon Color Spreading” was described by Varin (1971) and van Tuijl (1975). A display of thin rectangular spokes emanating radially from a central point, where the inner half of each spoke is red while the outer half is black, generates the vivid percept of the red color spreading to form a filled in red disc (radius the length of the red portion of the spokes). We wondered if there is an analogous effect for depth from binocular disparity. Corresponding to the color spreading displays, we made binocular displays consisting of thin rectangular spokes on a white background emanating radially from a central point. The spokes were made of random closely-spaced black dots. The disparity of the inner 1/3 of each spoke was set to give them the appearance of far depth (or of a depth slant through the plane of the screen), while the remaining spoke lengths had zero disparity so as to appear in the plane of the screen. Upon fusing the binocular stimuli, the perceived depth of the inner spokes spread so that the white space of entire inner disc region appeared to be displaced in depth (or as a disk slanted in depth), with a sharp border between the disk and the plane of the screen. Detailed depth-matching measurements across the sharp border perceived in the white inter-spoke region quantified the abrupt depth jump in the absence of local disparity cues. We conclude that perceived depth not only participates in the spreading phenomenon corresponding to the color effect but can propagate along sharp edges for long distances from the defining disparity information. This observation challenges classic models of depth propagation according to an isotropic smoothness constraint and suggests the need for strong anisotropic propagation in depth reconstruction models.
Support provided by grant FA9550-09-1-0678 to CWT.