Deficits in language-mediated mental operations in patients with schizophrenia

We found previously that a subgroup of schizophrenic patients who passed screening tests of attentional competence showed memory deficits on word memory tasks, but were comparable with controls on tone memory tasks. To better understand the nature of language-specific memory deficits in this subgroup of patients, the present experiment was designed to bypass early perceptual processing of verbal material and determine if patients continue to show impaired performance on verbal memory tasks. Patients who passed the screening tests ('discriminator' patients; DSz) received four serial position tasks. In two, familiar sounds or line drawings were presented and subjects were required to remember the word associated with each stimulus item. In the other two, subjects received hard-to-label auditory and visual stimuli (birdsongs or snowflakes). DSz patients showed large memory deficits compared with controls when required to remember words associated with the familiar sounds or drawings, providing clear evidence of deficits in verbal memory processes independent of sensory processing of verbal stimuli. The interaction between diagnosis and labeling was highly significant, confirming that these patients have particular difficulty with verbal as opposed to non-verbal memory. This was particularly striking on the auditory tests where two patients out-performed all controls on the birdsong test, but were below all controls on the easy-to-label sounds test. The verbal memory tests were easier than the non-verbal memory tests for controls, thus deconfounding task difficulty and deficit specificity.