Role of processing speed and premorbid IQ on visual recognition in patients with schizophrenia

Previous research had shown that processing speed and premorbid IQ are predictors of verbal-memory efficiency in patients with schizophrenia. We investigated whether the same factors are involved in visual memory. A total of 49 patients with schizophrenia and 43 healthy controls were administered a picture recognition task. Half of the pictures were black and white, and half were in color, in order to vary the depth of encoding. Processing speed was measured by three standard tasks, and premorbid IQ was measured by the National Adult Reading Test (NART). Patients were significantly impaired in picture recognition. Regression analyses revealed that NART score was a significant predictor of the recognition of both types of picture in patients. Processing speed was a significant predictor of the recognition of the colored pictures. The effect of diagnosis on the recognition of colored pictures was reduced to nonsignificance when processing speed was entered in the regression. These data suggest that premorbid IQ is involved in visual-recognition efficiency. However, the deficit observed in patients is accounted for by decreased processing speed.