Computational protocol: Sex, symptom, and premorbid social functioning associated with perceptual organization dysfunction in schizophrenia

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Protocol publication

[…] The Jittered Orientation Visual Integration (JOVI) task is a test of contour integration that determines a participant's ability to integrate Gabor elements into a perceptual whole. Gabor elements are sinusoidal luminance distributions that are Gaussian modulated (Silverstein et al., ; Uhlhaas et al., ). That is, Gabor elements show lower contrast at the edges compared to the center, and luminance varies from white to black in a gradually alternating fashion (Figure ). Gabor elements are considered to activate orientation-selective feature detectors in the primary visual cortex (Angelucci and Bullier, ), and are therefore a useful means to study their integration in early visual processing.The stimuli presented for this task are based on our recent study of contour integration in schizophrenia (Silverstein et al., ). Participants were shown static Gabor elements arranged in an oblong shape forming a contour embedded in a display of randomly oriented Gabor elements. The degree of orientation jitter of contour Gabor elements varied across six conditions (±0°, 7–8°, 9–10°, 11–12°, 13–14°, 15–16°), and this manipulation placed increasing degrees of burden on perceptual organization processes (i.e., at higher jitter levels, the correlations between adjacent element orientations become weaker, contour smoothness is increasingly disrupted, and contour perception becomes more difficult). For all stimuli, the ratio of the density of adjacent background elements to the density of adjacent contour elements was 0.9. Because adjacent background elements were, on average, closer together than adjacent contour elements, perceptual organization processes used to process contours are independent of density cues for this task (Silverstein et al., ).All JOVI stimuli trials were presented for 2 s followed by a 1 s inter stimulus interval during which responses were no longer recorded. There were 48 stimulus trials per jitter condition which were presented in blocks of 12 trials by condition. In addition, two types of catch stimuli (no errors expected) using 0° jitter were administered during each block to assess for attention lapses. One catch trial type had curved lines drawn through the contours (to eliminate the need for perceptual organization), and the other contained contour elements without any background elements (to remove effects of noise). The JOVI is a symmetric 1-alternative forced choice task where subjects responded whether the narrow end of the oblong contour was pointing left or right (Figure ). The task and stimuli patterns were created using E-prime (Psychology Software Tools, Pittsburgh, PA). [...] All data were analyzed using IBM SPSS Statistics 19. The demographic, clinical and perceptual data were compared between male and female participants using independent samples t-tests or χ2 square tests to analyze categorical variables (Table ). Spearman correlations were performed to examine the associations among demographic factors, PAS factors, PANSS factors and perceptual scores (Tables –).For multiple regression analyses, in cases where correlational analyses identified significant predictors of task performance that were predicted a priori (e.g., poor premorbid social functioning, disorganized symptoms), hierarchical regression analyses were employed in order to determine the extent to which each significant predictor accounted for variance in the dependent variable over and above that of other predictors, in addition to which variable alone accounted for the greatest proportion of variance in test score. In cases where correlational analyses indicated significant predictors that were not predicted a priori, stepwise regression was used to determine the descending order in which these predictors accounted for variance in the dependent variable.For the contour integration (JOVI) task, the mean score across all jitter conditions was used as the performance index since a previous study suggested higher test-retest reliability for the overall mean score compared to threshold values (Silverstein et al., ). Study participants with JOVI catch trial scores below 90% were excluded from all data analyses (n = 22). For the Ebbinghaus illusion task, a difference score index was computed: [(Helpful Context 2 Pixel Condition-No Outer Context 2 Pixel Condition)—(Misleading Context 2 Pixel Condition-No Outer Context 2 Pixel Condition)], which reflected overall context sensitivity. […]

Pipeline specifications

Software tools E-Prime, SPSS
Applications Miscellaneous, Neuropsychology analysis
Organisms Homo sapiens