Preattentive and focal attentional processes in schizophrenia: a visual search study.

Using a visual search task, the present study investigated preattentive and focal attentional processes in schizophrenic patients. The performance of 15 schizophrenic patients and 20 normal subjects was compared in three search tasks: feature search, 2-D feature search, and conjunction search. The target item was a red 'X' in all search tasks, and the distractor items were red 'O' in the feature search, green 'O' in the 2-D feature search, and red 'O' and green 'X' in the conjunction search. Set size total number of items presented in the display was 4, 16, or 25. Reaction times (RTs) for the subject's correct detection of target presence and absence were measured, and slopes of linear function relating RT to set size were computed. In the feature and the 2-D feature search, the schizophrenic subjects showed nearly zero slopes as did the normal subjects, indicating that in the preattentive process the schizophrenic patients functioned at a normal level. In the conjunction search, the schizophrenic subjects showed steeper slopes than the normal subjects for target absence (but not for target presence), suggesting that there was a deficit in the focal attentional process. Those results are consistent with the view of Callaway and Naghdi (1982) that a deficit in schizophrenic patients is mainly confined to the attentional process (cf., Lieb et al., 1994).