Perceptual and conceptual disorganization in schizophrenia: Two sides of the same coin?
16.503, Friday, May 10, 5:30 - 8:00 pm, Vista Ballroom
Brian Keane1,2,3, Jamie Joseph4, Steve Silverstein1,2; 1Department of Psychiatry, UMDNJ--Robert Wood Johnson Medical School, 2University Behavioral HealthCare, UMDNJ, 3Center for Cognitive Science, Rutgers University, New Brunswick, 4Graduate School of Biomedical Sciences, UMDNJ-Rutgers, New Brunswick
Background. People with schizophrenia are impaired at representing Kanizsa shapes, but why? Here, we hypothesize that the impairment arises at late processing stages, and is intimately related to disorganized thinking. Method. To consider the hypothesis, we had 13 healthy controls, 17 patients with disorganized schizophrenia, and 54 patients with non-disorganized schizophrenia engage in a "fat/thin" discrimination task (Ringach & Shapley, 1996). Subjects determined on each trial whether four individually rotated pac-men formed a fat or thin rectangle (illusory condition), or whether four downward pointing pac-men were all rotated to the left or right (fragmented condition). Half of the trials in each condition incorporated distractor lines, which disrupt discrimination when appearing near illusory contours but which can be ignored otherwise. Task difficulty depended on the amount by which pac-men were individually rotated to create the response alternatives, where larger rotations made for an easier classification. Performance was assessed with an adaptive staircase and threshold corresponded to the amount of rotation needed for 80% accuracy. Shape integration was measured as the threshold difference between the illusory and fragmented conditions (without distractors); a lower relative illusory threshold signifies better integration. Results. Distractor lines raised thresholds more in the illusory than in the fragmented condition (p<.001). This interaction did not depend on participant group (p>.7), suggesting that illusory contour formation was intact in all groups. However, disorganized patients were worse at shape integration than non-disorganized patients (p=.03) who in turn were marginally worse than controls (p=.07). Conclusion. People with schizophrenia form illusory contours but they are not able to use those contours to normally discern global shape. Shape integration impairments are especially pronounced among conceptually disorganized patients. These findings, taken together, show that schizophrenia entails a high-level visual integration deficit that is fundamentally related to disorganized thought.