Contour integration (CI) refers to the process that represents spatially separated elements as a unified edge or closed shape. Schizophrenia is a psychiatric disorder characterized by symptoms such as hallucinations, delusions, disorganized thinking, inappropriate affect, and social withdrawal. Persons with schizophrenia are impaired at CI, but the specific mechanisms underlying the deficit are still not clear. Here, we explored the hypothesis that poor patient performance owes to reduced feedback or impaired longer-range lateral connectivity within early visual cortex - functionally similar to that found in 5- to 6-year old children. This hypothesis predicts that as target element spacing increases from .7 to 1.4° of visual angle, patient impairments will become more pronounced. As a test of the prediction, 25 healthy controls and 36 clinically stable, asymptomatic persons with schizophrenia completed a CI task that involved determining whether a subset of Gabor elements formed a leftward or rightward pointing shape. Adjacent shape elements were spaced at either .7 or 1.4° of visual angle. Difficulty in each spacing condition depended on the number of noise elements present. Patients performed worse than controls overall, both groups performed worse with the larger spacing, and the magnitude of the between-group difference was not amplified at the larger spacing. These results show that CI deficits in schizophrenia cannot be explained in terms of a reduced spatial range of integration, at least not when the shape elements are spaced within 1.5°. Later-developing, low-level integrative mechanisms of lateral connectivity and feedback appear not to be differentially impaired in the illness.
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Acknowledgments We would like to thank the following Research Assistants for helping to bring this project to completion: Robin S. Lyons, Yushi Wang, Jamie Joseph (UMDNJ); Emily Thomason, Cindy Feldt, Jennifer Shuite, Melissa Cornejo (Washington University, St. Louis); Sharon August, Leeka Hubzin, Samual Kaiser, Tatyanna Matveeva (MPRC); Dori Henderson, Madelyn Steen, Anna Schnurrer, Joe Lowinske, Lindsay Swanson (Minnesota); and Brit-taney Haley (UC-Davis). We also appreciate the input of four anonymous reviewers whose extensive comments improved the manuscript. Funding for this research was provided by the following collaborative RO1s: MH084828-01 to SMS (UMDNJ), MH84840 to DMB (Washington University, St. Louis), MH084826 to CSC and JDR (UC Davis), MH084821 to JG (MPRC), and MH084861 to AM (Minnesota). Support from an F32 (MH094102-01A1) was provided to BPK (UMDNJ/Rutgers) during the write-up of the manuscript.
- Contour integration
- Perceptual organization
- Spatial range
- Visual integration