Abstract
Shadows can serve as a strong cue for 3D shape perception and lead to illusions of depth perception. In orthographically captured satellite images and aerial photographs, shadows serve as the primary depth cue, but this is usually accompanied by various other secondary ones, such as color, texture and relative size. In line with the literature, we have previously demonstrated that when such secondary cues are removed, i.e., a terrain is represented only based on shading, varying the light direction can lead to dramatic differences on how depth is perceived: Specifically, the south-eastern illumination leads to total reversal of depth perception, whereas north-western illumination angles lead to nearly zero reversal effect. This illusion has been named terrain reversal (or relief inversion) effect. Here we examine effects of cue integration, specifically the contributions of texture, color and stereoscopic viewing to the terrain reversal effect in two controlled lab experiments (n=27 and n=33, counterbalanced for biological sex and expertise). Our findings suggest photo-textures help bypassing the illusion, however, curiously grayscale more than color textures. Stereo also helps bypassing the illusion to some degree. Both of which we attribute to participants recognizing land cover elements, specifically because expert participants can bypass the illusion more often than others, and more often with satellite images than with shaded relief maps. To verify if this is indeed the case, eye movement data was also collected in these experiments to better understand why some participants are able to bypass the illusion more than others.