Abstract
Introduction: Perhaps the best known depth inversion illusion (DII) is the hollow-face illusion, in which a concave face mask is misperceived as convex; when it rotates, it is perceived rotating in the opposite direction. DII is possible with other concave objects, even with a hollow ovoid surface, but the illusion strength is much weaker. Two possible causes for the hollow-face illusion are a general convexity bias and face-specific stored knowledge that influences the visual input. The current project aimed to look for these effects in the presence of abstract facial and non-facial features. Method: We generated six computer-rendered 3D wire-frame objects that shared the same bounding contour; the bounding contour was a planar closed oblong wire-frame shape that resembled the outline of a frontal view of a face. Each object had a concave and a convex side. The two face-like objects were: (1) FN, with eyebrows and nose contour; (2) FNM, same as FN, with added mouth. The non-face objects were: (3) nFX, with two crossing diagonal contours; (4) nFV, with two nearly vertical non-crossing contours; (5) fNH, with nose, eyebrows and mouth rotated 90° clockwise. The last stimulus, (6) F+nF was the union of FNM and nFX stimuli. To provide kinetic depth information, each object was rotated clockwise or counterclockwise at 10 degrees/second. Results: DII was present for both concave and convex objects, but significantly stronger for concave objects (convexity bias). DII was equally strong for FN and FNM. DII was significantly stronger for face than for non-face stimuli. Performance with F+nF was closer to non-face than to face stimuli. Conclusions: Results suggest that DII is stronger for concave objects for both face and non-face stimuli, providing support for a general convexity bias. The increased frequency of DII occurrence for face-like objects indicates the presence of face-specific influences.
Meeting abstract presented at VSS 2018