Lack of flexibility in visual grouping in patients with schizophrenia.

The study attempted to distinguish automatic grouping processes from top-down processes in a visual perceptual task in 30 patients with schizophrenia and 30 matched controls. Participants decided whether 7 figures were all different or whether 2 adjacent figures were identical. The distance between figures was manipulated to produce 3 separated pairs of figures, the targets belonging to either the same pair (within-group trials) or different pairs (between-groups trials). As controls, patients benefited from proximity for grouping. Top-down processes were explored by manipulating the proportion of within-group and between-groups trials in 3 experimental blocks. In patients, response times (RTs) decreased for within-group trials when within-group trials were more frequent, indicating that performance was correctly adapted to the type of block. Unlike controls, however, this RT decrease was not accompanied by a cost for between-groups trials. Ocular movement recordings revealed that controls were able to focus on between-groups regions selectively when between-groups trials were more frequent, whereas patients were unable to do so. The authors suggest that top-down processes allowing the construction of a selective representation of between-groups regions are impaired in patients with schizophrenia. (c) 2008 APA, all rights reserved