Preattentive information processing in schizophrenia.

Preattentive and attentive information processing was investigated in 24 schizophrenic patients and 24 control subjects using a texture discrimination task based on Julesz's texton theory. Texton theory essentially defines a certain limited number of texture elements that can be detected readily and simultaneously without attentional effort irrespective of the size and information content of the rest of the visual field. During the first task, subjects had to detect texton elements (one 'L' among 35 '+'), which were presented on slides for 40 ms and were followed by a mask after different stimulus onset asynchronies (SOA: 200-800 ms). At all SOAs tested schizophrenics reported significantly fewer correct responses compared to the control group. In the second task, subjects had to search for texton (one 'L' among 35 '+') and non-texton elements (one 'L' among 35 'T') in the stimulus displays, whereby response times were measured. Schizophrenics showed significantly slower response times only to texton elements, whereas response times to non-texton elements did not significantly differ from controls. Additionally, schizophrenics made significantly more errors detecting non-texton elements than controls. The results suggest a deficit in processing of visual information in schizophrenic patients, which is confined to preattentive processes and may consist of a slowing of those processes. Schizophrenics may also have difficulty in sustaining their attention during search tasks.