Memory in schizophrenia: what is impaired and what is preserved?

This study assesses the pattern of long-term memory performance in a sample of 12 schizophrenic patients who were selected on the basis of showing a memory deficit in the absence of gross overall intellectual impairment. When compared with 12 control subjects matched for age, sex and estimated premorbid IQ, presence of an episodic memory deficit was confirmed for both prose recall and forced-choice word and face recognition. Semantic memory was assessed using the sentence verification task developed by Collins and Quillian, an unpaced category judgement task, and the Mill Hill Vocabulary Scale. The schizophrenic patients were slower on sentence verification and they made significantly more errors in all three tasks. Procedural tasks included pursuit rotor performance, speed of repeatedly assembling a jigsaw puzzle and rate of improvement in reading transformed script. Here, while the schizophrenic patients showed poor overall performance on the pursuit rotor and jigsaw learning, their rate of learning on all three procedural tasks was comparable with that of the controls. When examined on two implicit memory tasks involving biasing of spelling of homophones and word stem completion, the patients showed a normal degree of priming in both. Implications for the nature of the memory deficit in schizophrenia are discussed.