Abstract
Perceptual organization, which refers to the ability to integrate fragments of stimuli to form a representation of a whole edge, part, or object, is impaired in schizophrenia. A contour integration paradigm, involving detection of a set of Gabor patches forming an oval contour pointing to the right or left embedded in a field of randomly oriented Gabors, has been developed for use in clinical trials of schizophrenia. The purpose of the present study was to assess contributions of early and later stages of processing to deficits in contour integration, as well as to develop an event-related potential (ERP) analog of this task. Twenty-one patients with schizophrenia and 28 controls participated. The Gabor elements forming the contours were given a low or high degree of orientational jitter, making it either easy or difficult to identify the direction in which the contour was pointing. ERP results showed greater negative peaks at ~165 (N1 component) and ~270 ms for the low-jitter versus the high-jitter contours, with a much greater difference between jitter conditions at 270 ms. This later ERP component was previously termed Ncl for closure negativity. Source localization identified the Ncl in the lateral occipital object recognition area. Patients showed a significant decrease in the Ncl, but not N1, compared to controls, and this was associated with impaired behavioral ability to identify contours. In addition, an earlier negative peak was found at ~120 ms (termed N120) that differentiated jitter conditions, had a dorsal stream source, and differed between patients and controls. Patients also showed a deficit in the dorsal stream sensory P1 component. These results are in accord with impairments in distributed circuitry contributing to perceptual organization deficits and provide an ERP analog to the behavioral contour integration task.
Highlights
Visual integration, referred to as “perceptual organization,” is impaired in schizophrenia (Silverstein and Keane, 2011)
The present paper focuses on a visual integration paradigm that has been widely used in schizophrenia—contour integration (Field et al, 1993; Silverstein et al, 2000, 2006, 2012; Uhlhaas and Silverstein, 2005; Kozma-Wiebe et al, 2006; Silverstein and Keane, 2011)
A significant group × jitter interaction was found [F(1, 47) = 4.1, p = 0.05, η2p = 0.081], indicating lack of differential current source density (CSD) to low versus high jitter in patients [F(1, 20) = 0.001, p = 0.97, η2p < 0.001] but differential CSD to the jitter conditions in controls [F(1, 27) = 11.5, p = 0.002, η2p = 0.298, a large effect size; (Pallant, 2007)]
Summary
Referred to as “perceptual organization,” is impaired in schizophrenia (Silverstein and Keane, 2011). The importance of visual integration impairments is underscored by inclusion of this domain as a core construct in the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) initiative (Green et al, 2009; Butler et al, 2012; Silverstein et al, 2012). Visual integration deficits are seen on a number of tasks in schizophrenia including contour integration (Silverstein et al, 2000, 2006, 2012; Uhlhaas and Silverstein, 2005; Kozma-Wiebe et al, 2006; Silverstein and Keane, 2011), coherent motion (Chen, 2011), object recognition from fragmented line drawings (Doniger et al, 2002; Sehatpour et al, 2010), grouping according to proximity or color similarity (Kurylo et al, 2007), and configural processing of faces (Silverstein et al, 2010). A salient aspect of these studies is that they do not appear to be due to a “general deficit,” in that patients perform more accurately than controls when the task relies on judgments about individual features or when grouping interferes with isolating or processing single features (Place and Gilmore, 1980; Silverstein and Keane, 2011)
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