Storage and Access Procedures in Schizophrenia: Evidence for a Two Phase Model of Lexical Impairment

Abstract

Evidence has accumulated to show that schizophrenia is characterized by lexical-semantic difficulties; however, questions remain about whether schizophrenics have problems in accessing intact representations or a loss of the representations themselves. Both access and storage types of disorder have been reported and it has been speculated that this may reflect a transition from the former to latter with increasing length of illness. This study investigated whether illness duration, age or estimated premorbid IQ predict the size and accessibility of the lexical store. Fifty-six schizophrenic patients (chosen to represent a wide range of illness duration from 3–40 years) and 24 matched healthy controls were asked to name 120 pictures on two occasions. Estimates of store size and retrieval probability were derived from a two parameter stochastic Markov chain model. This revealed that even early in the course of illness, schizophrenics appear to have suffered a reduction in lexical store size and that those with longer length of illness show deficits in both their store size and their ability to retrieve names from that store.

Notes

¹ Whilst the effect of creating the appearance of store type difficulties in subjects with lower IQ was due to the difficulty of the naming test utilized in this study, it was necessary to use a test where performance was not at the ceiling in the control group thus we feel that this choice was justified.