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Thomas Papathomas, Nicola Bruno, Attila Farkas; The role of binocular disparity in depth-inversion illusions studied with synopters and pseudoscopes. Journal of Vision 2018;18(10):497. doi: 10.1167/18.10.497.
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Introduction: Depth-inversion illusions (DII) offer examples in which stored knowledge overcomes visual cues and causes 3D objects to be perceived in opposite depth: points located physically closer appear to be behind points located physically further, thus transforming convexities into perceived concavities and vice versa. Viewers moving in front of DII stimuli perceive them to move (illusory DII motion). We manipulated the binocular disparity (BD) cue to study its role in DII. Methods: We used large (height > 80 cm) realistically painted hollow masks (HM) and reverse-perspectives (RP) as DII stimuli (DIIS); painted cues and the 3D geometry were incongruent. We also used their depth-opposites: a normal 3D mask (NM) and a proper-perspective (PP) that are normally not depth-inverted stimuli (nDIIS). Subjects viewed DIIS (HF and RP) and nDIIS (NM and PP) from 3 meters, monocularly and binocularly, as well as using a synopter (identical eyes' views, BD=0) and a pseudoscope (left and right eye views swapped; BD is the negative of its value under normal viewing). Results: DII was strongest under pseudoscopic viewing and weakest under binocular viewing, with synoptic and monocular viewing yielding intermediate strengths as expected, for both DIIS. DI was impossible for nDIIS under all conditions. It was nearly impossible when viewers saw only the top or only the bottom parts of nDIIS for all conditions, but it became possible under pseudoscopic viewing. Illusory motion was always present when DII was present. Conclusions: BD opposes DII under binocular viewing, because it signals veridical depth. As expected, DII strength increases under monocular or synoptic viewing (BD=0), reaching its maximum under pseudoscopic viewing, because BD signals illusory depth under pseudoscopy. The above confirms BD as a strong cue for recovering 3D shape. However, BD's weak effect on nDIIS indicates its limits as a cue for 3D shape recovery.
Meeting abstract presented at VSS 2018
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