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Michael-Paul Schallmo, Scott Sponheim, Cheryl Olman; Contextual Modulation of Contour Detection is Altered in Schizophrenia. Journal of Vision 2011;11(11):1050. doi: 10.1167/11.11.1050.
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Contour detection is an important step in early visual processing that facilitates figure-ground segmentation and object recognition. Patients with schizophrenia show abnormalities in early visual processing, and contour detection deficits have been observed in those with this disorder. It has recently been shown that during contour detection, nearby elements that are not part of a contour can influence detection thresholds, an effect referred to here as contextual modulation. The valence of this modulation depends on the relative orientation between contour elements and flankers, and agrees with known orientation selective surround suppression (OSSS) effects. It has also been shown that the OSSS effect is diminished in subjects with schizophrenia. However, is it currently unknown how deficits in OSSS in schizophrenia may influence contextual modulation by flanking elements during contour detection. Therefore, we measured contour detection thresholds in healthy adults and those with schizophrenia in a psychophysics experiment. Stimuli consisted of an array of Gabor elements with a vertically oriented group of elements forming a target contour to the left or right of fixation. Thresholds were obtained by determining a subject's tolerance to jitter in the orientation of target elements. Stimulus context differed between conditions, and was defined by the relative orientation between contour elements and flankers (5 Gabors flanking left & right of both possible target locations). Within subject groups, thresholds for randomly or orthogonally oriented flankers are significantly higher than for parallel flankers. In general, subjects with schizophrenia performed better on the task than healthy controls, with a significant increase in performance in the orthogonal condition, relative to randomly oriented flankers, that was not observed in controls. Increased performance in the orthogonal condition constitutes a context-specific visual processing abnormality during contour detection, and suggests broader tuning of orientation-dependent lateral masking effects in schizophrenia.
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