Kanizsa shape discrimination and contour integration deficits in schizophrenia: What is the role of spatial frequency?
36.514, Sunday, May 12, 2:45 - 6:45 pm, Vista Ballroom
Timur Suhail-Sindhu1, Brian P. Keane1,2,3, Danielle Paterno1, Genna Erlikhman4, Sabine Kastner5,6, Steven M. Silverstein1,2; 1Center for Cognitive Science, Rutgers University, New Brunswick, 2University Behavioral HealthCare, UMDNJ, 3Department of Psychiatry, UMDNJRobert Wood Johnson Medical School, 4Department of Psychology, University of California, Los Angeles, 5Princeton Neuroscience Institute, Princeton University, 66Department of Psychology, Princeton University
Introduction. Patients with schizophrenia exhibit a reduced ability to distinguish Kanizsa shapes and integrate collinear elements (gabors). Patients also poorly process low spatial frequencies (SFs), which reflects dysfunction along the magnocellular pathway. Here, we ask: Will patients perceptual organization deficits disappear when low SFs are removed from the stimuli? Method. To address this question, we tested 11 patients and 9 healthy controls on two classic paradigms. In the contour integration task, subjects identified the screen quadrant in which a closed chain of co-circular gabors appeared. Task difficulty depended on the number of noise gabors co-presented with the target, and the stimulus was scaled to produce two SF conditions (4 and 12 cycles/deg). In the discrimination task, subjects determined on each trial whether four pac-men formed a fat or thin Kanizsa shape (illusory condition) or whether four downward-pointing pac-men were rotated left or right (fragmented condition). The pac-men were presented with all SFs (broadband) or with low SFs removed. Task difficulty depended on the amount by which the pac-men were individually rotated, and illusory shape discrimination was measured as the performance difference between the illusory and fragmented conditions. Results. Patients are at least marginally worse at contour integration and illusory shape discrimination, and such differences do not depend on SF structure. Moreover, contour integration and illusory shape discrimination are strongly correlated for both groups, suggesting a common underlying mechanism. Conclusions. The ability to distinguish Kanizsa shapes and detect gabor chains is reduced in schizophrenia, perhaps as a result of a disturbance to a common underlying mechanism. Crucially, illusory shape discrimination and contour integration deficits in SZ cannot be explained in terms of poor low SF processing, and therefore probably cannot be explained in terms of magnocellular dysfunction.