Working memory, intelligence and knowledge base in adult persons with intellectual disability

Previous studies have suggested that performance in working memory (WM) tasks is deficient in all etiologies and at all levels of intellectual disability (ED). Knowledge about WM structure, cognitive processes reflected in WM tasks, or the long-term memory contribution to W-M capacity in ED is, however, not satisfactory. In the present study, WM capacity, WM task requirements, as well as effects between WM, skills, knowledge base, and intelligence were explored in two groups with matched fluid intelligence: adult persons with ID and normally developing children aged 3-6 years. The ED Group performed equally well as the children in WM tasks based on familiar semantic information and were significantly better on all measures reflecting skills and knowledge base. The Child Group performed better in phonological and visuo-spatial WM tasks including nonsemantic information, respectively. In particular, it appeared that the groups differed in their WM performance although they were matched for fluid intelligence. We hypothesize that the ID Group depended more on knowledge support from long-term memory whereas the Child Group could benefit more from efficient online WM processes. (C) 2002 Elsevier Science Ltd. All rights reserved.