Written numeral transcoding in patients with Alzheimer's disease

Transcoding verbal numerals into Arabic numerals and vice versa was studied in 21 patients with probable Alzheimer's disease and 22 healthy subjects. Transcoding errors were analyzed according to the classification schemes by Deloche and Seron (1982a, 1982b) and Seron and Deloche (1983). In the control group, errors occurred only 2% of the time in transcoding Arabic numerals into verbal numerals, and in 1.4% for the reverse order. In AD patients, more than one error frequently occurred in the same item. In 672 transcriptions from Arabic numerals into verbal numerals 479 errors occurred in 312 items. In the reverse order 672 transcriptions were performed and 290 errors occurred in 238 items. One kind of error was striking in both transcoding directions, not reported in aphasic or other brain damaged patients: elements of the source code reappeared in the target code, e.g. 3436--> 3tausendvierhundert36 (3 thousand four hundred 36), or zweihundertelf (211)-->2hindert11 (2hundred11). It is concluded that this error type is the result of a cognitive system which has multiple impairments and in which control mechanisms are temporarily failing.