RATES OF FORGETTING IN ALZHEIMER DEMENTIA

Patients diagnosed with Alzheimer's disease (AD) were compared with he althy controls on a picture recognition task, a forced choice word rec ognition task, a forced choice design recognition task, a picture reca ll task and a stem completion task. Performance on recognition and wor d stem completion was assessed at 1, 10 and 20 min after exposure to e xperimental stimuli, as these are delays across which previous studies had suggested there might be differing forgetting rates. AD patients did not show significantly faster rates of forgetting relative to cont rols on picture recognition, design recognition, word recognition or s tem completion, after levels of learning had been matched as closely a s possible. Moreover, once initial learning was equated in a small num ber of subjects, there were no qualitative differences between AD pati ents and controls following inclusion and exclusion instructions on th e stem completion task. In particular, those AD patients who were matc hed to controls for initial levels of ''recollection'' showed comparab le forgetting rates in recollection (or cued recall). Although matchin g was more difficult for a picture recall task, both the main analysis and subgroup analysis indicated faster forgetting in the AD group tha n controls, suggesting a difference between ''free recall'' and recogn ition or cued recall measures, comparable with the finding in a parall el study of organic amnesia. (C) 1998 Elsevier Science Ltd. All rights reserved.