Why is contour integration impaired in schizophrenia? New insights from a cross-diagnostic parametrically varying behavioral task

Abstract

Background. Schizophrenia patients poorly integrate disconnected oriented elements into cohesive contours and shapes; the impairment worsens as the stimulus is globally scaled down in size (d=1.7; Keane et al., 2016). What stimulus features drive this scaling effect and how specific is it to schizophrenia? Addressing this issue will yield clues for building behavioral tasks that flag current or impending psychosis; it will also clarify the visual mechanisms disturbed. Methods. We compared schizophrenia patients (SZ; N=5), bipolar disorder patients (BD; N=9) and well-matched healthy controls (N=7) on a task in which subjects sought to identify the screen quadrant location of an integrated eight-element circular target. Task difficulty was staircase controlled and depended on the number of noise elements co-presented with the target. There were 16 different conditions corresponding to the crossings of four parameters that would change with spatial scaling: (1) Gabor spatial frequency (6 or 12 cycles/deg), (2) Gabor width (Gaussian envelope SD of 2.4 or 4.8 arcmin), (3) target eccentricity (2.3 or 4.7 degrees), and (4) target radius (.74 or 1.5 deg). Results. Subject group interacted with spatial frequency, eccentricity, and Gabor width (four-way interaction,p< .01); it also interacted with eccentricity, radius, and spatial frequency (four-way interaction, p< .05). Comparing controls and BDs, there were no group differences or interactions (ps>.05). Comparing SZs to controls and to BDs, there was the same four-way interaction with spatial frequency, eccentricity, and Gabor width (both p< .05). More specifically, increasing Gabor width improved performance more for lower than for higher spatial frequency Gabors; increasing eccentricity accentuated this two-way interaction for controls and BDs but not for SZs. Conclusion. Potentially all aspects of spatial scaling jointly contribute to contour integration deficits in SZ perhaps because of inadequate sampling within parafoveal relative to peripheral retinotopic locations. These deficits appear to be SZ-specific and thus cannot be attributed to general psychopathology (e.g., anxiety, medication)

Acknowledgement: K01MH108783