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Controlled Clinical Trial
. 2013 Jun 18;8(6):e68090.
doi: 10.1371/journal.pone.0068090. Print 2013.

Abnormal Contextual Modulation of Visual Contour Detection in Patients With Schizophrenia

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Free PMC article
Controlled Clinical Trial

Abnormal Contextual Modulation of Visual Contour Detection in Patients With Schizophrenia

Michael-Paul Schallmo et al. PLoS One. .
Free PMC article

Erratum in

  • PLoS One. 2013;8(10). doi:10.1371/annotation/f082ec4d-419c-43ce-ae50-e05107539bf3

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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Example Stimuli.
Top, Random condition. Target contours (composed of 5 Gabors) were presented in a vertical line in the second column to either the right (as shown in top example) or left of fixation. The Gabors horizontally adjacent to possible target positions are termed flankers, and were oriented randomly in this condition. The distribution of flanker orientations is shown at the top of each panel in brackets. Bottom left, zoomed region to show detail of Parallel condition. Average orientation of flankers (four sets bracketed in red) is parallel to the vertical contour axis. Target contour is presented on the left in both bottom panels. Flankers surrounded both possible target contour locations on every trial. Bottom right, detail of Orthogonal condition. Flankers (bracketed in blue) are on average oriented orthogonal to the vertical target contour.
Figure 2
Figure 2. Contour Detection Thresholds.
Mean contour detection thresholds are plotted for 28 healthy controls (circles), 13 first-degree relatives (squares), and 25 patients with schizophrenia (triangles) for the Parallel (red), Random (gray), and Orthogonal (blue) conditions. Example contours with 4.5° jitter (bottom) and 31.5° jitter (top) are shown along the y-axis. Error bars are S.E.M. Double asterisk indicates significant differences in Random condition thresholds between schizophrenia patients and both healthy controls and first-degree relatives, single asterisk indicates a significant difference in Orthogonal condition thresholds between patients and relatives. Corrected for multiple comparisons via Tukey’s HSD, p < 0.05.
Figure 3
Figure 3. Contextual Modulation Indices.
Mean indices are plotted for 28 healthy controls (circles), 13 first-degree relatives (squares), and 25 patients with schizophrenia (triangles) in the Parallel (red) and Orthogonal (blue) conditions. Negative indices indicate conditions where contour detection was suppressed relative to the Random condition, whereas positive indices indicate enhanced contour perception. Asterisk indicates a significant difference between schizophrenia patients and healthy controls, corrected for multiple comparisons via Tukey’s HSD, p < 0.05. Error bars are S.E.M.
Figure 4
Figure 4. Computational Modeling.
Computational model predications based on parameters from Table 2 for 28 control subjects (green solid lines) and 25 schizophrenia patients (purple dashed lines). A) Equation 1 was fit to contour detection task data in all three flanker conditions from healthy controls (circles) and patients with schizophrenia (triangles). Plotted thresholds are identical to those in Figure 2. Error bars are S.E.M. B) Bootstrapped estimates of T 0, c s and σs were used to calculate flanker suppression orientation tuning distributions (in arbitrary units) for the control and patient groups. Lines plot the mean bootstrapped tuning curves for patients and controls. Shaded regions illustrate 1 standard deviation of the bootstrapped distributions for each group. Gray arrows indicate corresponding positions in both panels.

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