Spelling and attention in early Alzheimer's disease: evidence for impairment of the graphemic buffer.

The present study was conducted to investigate the spelling ability of persons affected by mild Alzheimer's disease (AD). AD subjects produced more phonemically implausible (PI) spelling errors (e.g. enough-->enougigh) than normal subjects; in addition, AD subjects produced a higher percentage of PI spelling errors than normal AD subjects. We found that two clinical visual attention tests were better predictors of the number of PI spelling errors than a language measure. Moreover, we also found that AD subjects performed more poorly when they copied words that were viewed and removed from sight than when the same words were copied directly. In contrast, there was no significant difference in the performance of the normal elderly on direct and delayed copying tasks. AD subjects produced more errors when spelling long words than when spelling short words. Although the spelling performance of the normal elderly was also affected by the length of the words spelled, AD subjects showed a significantly greater drop in performance than normal subjects when the length of the words increased. The vocabulary of the short and long word lists did not differ in frequency of occurrence or imagability (i.e. abstractness). The results suggest that visual attention impairment and not language impairment accounts for the PI spelling errors of mild AD subjects. The results are discussed with reference to graphemic buffer deficits identified in case studies of stroke patients with dysgraphia.