Hannah Moser¹, Helen Yu¹, Killebrew Kyle¹, Scott Sponheim^2,1, Michael-Paul Schallmo¹; ¹University of Minnesota, ²Minneapolis VA Health Care System

People with psychotic disorders (e.g., schizophrenia, bipolar disorder) commonly experience abnormal visual perception, such as hallucinations. They also exhibit performance differences in paradigms designed to test visual context processing (e.g., contrast surround suppression). Here, we examined whether there are differences in contextual modulation of perceived size in people with schizophrenia (n=24) or bipolar disorder (n=16) diagnoses, as well as controls (n=39) without a history of psychosis, using an illusory size task (i.e., ‘ball in the hallway’). The task consisted of two checkerboard circles presented on the upper and lower parts of a screen, in the absence or presence of a hallway image. With the hallway, the lower circle appears relatively smaller than the upper circle due to contextual modulation by the background, even when the circles are the same angular size. We used an adaptive staircase procedure to measure the difference in perceived size of the circles in the absence versus presence of the hallway. Each participant group showed a significant condition effect, with the presence of the hallway decreasing the perceived size of the lower circle. The strength of this size illusion did not significantly differ between people with schizophrenia, people with bipolar disorder, or controls. A subset of participants also completed a self-report measure of real-world perceptual anomalies, the Sensory Gating Inventory (SGI). The size illusion was negatively correlated with SGI total scores (r(63)=-0.26, p=0.035), indicating reports of everyday perceptual anomalies were associated with weaker contextual modulation of perceived size. Our results suggest weaker perception of contextual size illusions may be related to anomalous perception regardless of diagnosis.

Acknowledgements: I01 CX001843, K01 MH120278, P41 EB027061, UL1 TR002494, T32 DA037183