Intrusion errors in numerical transcoding by Alzheimer patients

The errors made by brain-damaged patients when they attempt numerical trans coding tasks have recently been considered as a possible aid to early diagn osis of the disease. The transcoding errors of 20 Alzheimer's disease patie nts are described, and the incidence of each kind of error compared with no rms from healthy subjects. Tegner and Nyback (Tegner R, Nyback H. "To hundr ed and twenty4our'': a study of transcoding in dementia. Acta Neurologica S candinavia 1990; 81: 177-178) reported that Alzheimer patients often expres s numerical information in a mixture of verbal and digital codes and Kessle r and Kalbe (Kessler J, Kalbe E. Written numerical transcoding in patients with Alzheimer's disease. Cortex 1996: 32: 755-761) suggested that such int rusions of the source code into the target code may not only be largely abs ent from the responses of the healthy population, but also from the transco ding operations of patients with other kinds of brain damage, such as aphas ia. It was found that intrusion errors occurred much more frequently in the transcoding protocols of some of the Alzheimer patients than they do in th ose of healthy subjects. On the other hand, they were entirely absent from the protocols of other Alzheimer patients. The implications of the findings for the early diagnosis of Alzheimer's disease are discussed, and the phen omenon of intrusion errors is considered in terms of some of the models of arithmetical processing that have been proposed. (C) 2000 Elsevier Science Ltd. All rights reserved.