Cognitive dysfunction in first-episode psychosis: the processing speed hypothesis.

BACKGROUND Speed of processing is a cognitive process underlying cognitive dysfunction in people with chronic schizophrenia. AIMS To investigate the contribution of speed of processing to the cognitive deficits observed in a representative large sample with first-episode schizophrenia. METHOD People with a diagnosis of first-episode schizophrenia-spectrum disorders (n=26) and healthy controls (n=28) were compared on several cognitive measures before and after controlling for speed of processing. RESULTS Before controlling for speed of processing, patients and controls differed significantly on all cognitive measures. All significant differences in cognitive functioning disappeared when the result of the Digital Symbol Substitution Test was included as an additional covariate. CONCLUSIONS Speed of information processing may be considered a core cognitive deficit in schizophrenia and might be mediating a broader diversity of cognitive disturbances.