ILLUSORY CONJUNCTIONS AND PERCEPTUAL GROUPING IN A VISUAL-SEARCH TASKIN SCHIZOPHRENIA

This report describes part of a series of experiments, conducted withi n the framework of feature integration theory, to determine whether pa tients with schizophrenia show deficits in preattentive processing. Th irty subjects with a DSM-III-R diagnosis of schizophrenia and 30 age-, gender-, and education-matched normal control subjects completed two computerized experimental tasks, a visual search task assessing the fr equency of illusory conjunctions (i.e. false perceptions) under condit ions of divided attention (Experiment 3) and a task which examined the effects of perceptual grouping on illusory conjunctions (Experiment 4 ). We also assessed current symptomatology and its relationship to tas k performance. Contrary to our hypotheses, schizophrenia subjects did not show higher rates of illusory conjunctions, and the in influence o f perceptual grouping on the frequency of illusory conjunctions was si milar for schizophrenia and control subjects. Nonetheless, specific pr edictions from feature integration theory about the impact of differen t target types (Experiment 3) and perceptual groups (Experiment 4) on the likelihood of forming an illusory conjunction were strongly suppor ted, thereby confirming the integrity of the experimental procedures. Overall, these studies revealed no firm evidence that schizophrenia is associated with a preattentive abnormality in visual search using sti muli that differ on the basis of physical characteristics. (C) 1998 El sevier Science Ireland Ltd. All rights reserved.