Abnormal Contextual Modulation of Visual Contour Detection in Patients with Schizophrenia

Abstract

Schizophrenia patients demonstrate perceptual deficits consistent with broad dysfunction in visual context processing. These include poor integration of segments forming visual contours, and reduced visual contrast effects (e.g. weaker orientation-dependent surround suppression, ODSS). Background image context can influence contour perception, as stimuli near the contour affect detection accuracy. Because of ODSS, this contextual modulation depends on the relative orientation between the contour and flanking elements, with parallel flankers impairing contour perception. However in schizophrenia, the impact of abnormal ODSS during contour perception is not clear. It is also unknown whether deficient contour perception marks genetic liability for schizophrenia, or is strictly associated with clinical expression of this disorder. We examined contour detection in 25 adults with schizophrenia, 13 unaffected first-degree biological relatives of schizophrenia patients, and 28 healthy controls. Subjects performed a psychophysics experiment designed to quantify the effect of flanker orientation during contour detection. Overall, patients with schizophrenia showed poorer contour detection performance than relatives or controls. Parallel flankers suppressed and orthogonal flankers enhanced contour detection performance for all groups, but parallel suppression was relatively weaker for schizophrenia patients than healthy controls. Relatives of patients showed equivalent performance with controls. Computational modeling suggested that abnormal contextual modulation in schizophrenia may be explained by suppression that is more broadly tuned for orientation. Abnormal flanker suppression in schizophrenia is consistent with weaker ODSS and/or broader orientation tuning. This work provides the first evidence that such perceptual abnormalities may not be associated with a genetic liability for schizophrenia.

Late, not early, stages of Kanizsa shape perception are compromised in schizophrenia

“…An objection so far is that subjects may be performing worse on Kanizsa shape perception tasks because these individuals have broader orientation tuning curves, making them less sensitive to the slants of the edges that decide contour convexity (Robol, et al, 2013; Schallmo, Sponheim, & Olman, 2013). This is unlikely in our case because the highly influential disorganized patients had (non-significantly) lower fragmented thresholds than the non-disorganized patients and had similar fragmented thresholds to the healthy controls ( p =.244).…”

Multiple forms of contour grouping deficits in schizophrenia: What is the role of spatial frequency?

“…Others have argued for broad orientation tuning in schizophrenia and that this might underlie at least some forms of contour grouping deficits in schizophrenia (Robol et al, 2013; Schallmo et al, 2013). We found no difference in orientation discrimination in our fragmented task.…”

“…The problem is that the individual elements in clinical CG studies are Gabor patches—that is, oriented sinusoidal luminance gratings multiplied with a circularly symmetric Gaussian kernel—and the carrier frequencies were almost always below 8.3 cycles/deg. In some cases, the SF was 6.7 cycles/deg (Keri, Kelemen, & Benedek, 2009; Keri, Kelemen, Benedek, & Janka, 2005; Keri, Kiss, Kelemen, Benedek, & Janka, 2005; Must, Janka, Benedek, & Keri, 2004); in other cases, it was 5 cycles/deg (Kozma-Wiebe et al, 2006; Silverstein et al, 2009; Silverstein, Kovacs, Corry, & Valone, 2000), and in still other cases, it was less than 4 cycles/deg (Robol et al, 2013; Schallmo, Sponheim, & Olman, 2013). It is thus entirely possible that the reason that patients perform poorly in grouping tasks owes not to an integration deficit per se , but to a problem in detecting or accurately representing the elements integrated.…”

On the functions, mechanisms, and malfunctions of intracortical contextual modulation

“…For example, patients have demonstrated weaker suppression for contrast (Dakin, Carlin and Hemsley, 2005;Tibber et al, 2013), and size (Uhlhaas et al, , 2006Silverstein et al, 2013), with mixed evidence on orientation (Schallmo, Sponheim, and Olman, 2013;Tibber et al, 2013;Yoon et al, 2009Yoon et al, , 2010. There is negative evidence in the case of luminance, the earliest processed of the dimensions studied, and that suggests a cortical locus for reduced surround suppression .…”