Abstract
Background. Schizophrenia patients poorly integrate oriented elements into cohesive contours. The deficit worsens as the stimulus is globally scaled down in size (Keane et al., 2016), but it is unknown which stimulus features are driving this scaling effect or whether they are diagnostically specific. Addressing this issue could suggest new behavioral tools for flagging current or impending psychosis; it could also clarify the visual mechanisms disturbed. Method. We compared schizophrenia patients (n=19), bipolar disorder patients (n=16), and well-matched healthy controls (n=25) on a task in which subjects sought to identify the quadrant location of an integrated circular target embedded in noise. Task difficulty was staircase controlled and depended on the number of noise elements co-presented with the target. There were 16 conditions corresponding to the crossings of four parameters that would change with spatial scaling: (1) spatial frequency (SF; 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). A five-way ANOVA (with subject group) revealed the stimulus properties that might amplify group differences. Results. Subject group interacted with SF but not with any other factor or combination of factors. Follow-up ANOVAs showed group differences for high but not low SF stimuli. After collapsing performance across the high SF conditions, each patient group performed worse than controls (ps<.03, ds>.88) but comparably to one another (p>.6, d<.17). Discussion. High SF stimuli similarly contribute to contour integration deficits in schizophrenia and bipolar disorder; this happens independently of other scaled stimulus attributes. Our results further demonstrate that seemingly subtle stimulus features can play a powerful role in determining whether any group deficit is observed.