Three-dimensional depth illusions in schizophrenia and bipolar disorder

Abstract

Purpose: People with schizophrenia are less likely to perceive physically concave objects as convex (as in the hollow mask illusion). Are reduced depth illusions specific to schizophrenia or do they also occur in other illnesses in which psychotic symptoms occur, such as bipolar disorder? Method: We compared a bipolar group (N=13) to previously examined healthy control (N=25) and schizophrenia (N=30) groups. Subjects made convexity judgments about 5 physical objects. Two were concave scenes ("reverspectives"), two were concave faces, and one was a convex face (catch stimulus). A reverspective and a concave face were painted with life-like texture; the remaining objects were uniformly colored. All five objects were viewed twice—once monocularly with the subject moving left-right (to create motion parallax) and once stereoscopically with the subject stationary (to isolate the role of binocular disparity). For each viewing, subjects were probed every 12 seconds over 2 minutes on whether the object appeared convex or concave. Results: There were no significant differences between the three subject groups in perceiving the catch stimulus (p>.4). For concave objects, schizophrenia patients gave more accurate (veridical) responses than controls (p<.05) but bipolar patients did not differ significantly from either of the other groups (p>.12). However, the group comparisons depended on symptoms: The 15 most psychotic schizophrenia patients clearly differed from the bipolar and control groups (p<.05); the 15 least psychotic patients differed from neither the bipolar nor control group. None of the group differences depended on texture, object-type or viewing condition (ps>.24). Conclusions: We conclude that concave objects produce fewer depth illusions in schizophrenia than bipolar disorder but only if schizophrenia patients are sufficiently psychotic. We also found that the group difference is constant across different object types and viewing conditions, suggesting that positive symptoms may disrupt a generic convexity prior. Meeting abstract presented at VSS 2013