Memory and schizophrenia: differential link of processing speed and selective attention with two levels of encoding

The purpose of this study was to investigate how underlying cognitive defic its such as a defect in processing speed or in selective attention contribu ted to different types of memory impairment observed in schizophrenia (supe rficial vs deep encoding). 49 schizophrenic patients and 40 normal controls were administered a verbal memory task. Superficial encoding was assessed by the ability to recall items in their serial order. Deep encoding was ass essed by the ability to organise words into semantic categories. Two measur es of processing speed (Digit Symbol Substitution Test and Stroop colour ti me) and one measure of selective attention (Stroop test) were used. Regress ion analyses were carried out. In the patient group, processing speed contr ibuted to both superficial and deep encoding, and to a global verbal memory score. Selective attention only contributed to the superficial encoding pr ocesses. Thus, slowing of processing speed in schizophrenia seems to be mor e crucial for memory performance, since it affects memory in a pervasive wa y. (C) 2000 Elsevier Science Ltd. All rights reserved.