Impaired spelling in Alzheimer's disease: a linguistic deficit?

Different kinds of real words and pronounceable pseudowords (PWs) were presented for writing to dictation to patients with the diagnosis of probable Alzheimer's disease (AD) and to age- and education-matched healthy controls. Though spelling less accurately on all tasks, AD patients responded in a manner generally qualitatively similar to controls. Except for a slightly enhanced effect of spelling regularity in real word writing accuracy, AD patients showed the same sensitivity to various lexical, orthographic and phonological variables as controls. Both groups showed no difference in spelling accuracy for words and PWs with regular vs ambiguous spelling patterns, and groups also showed similar orthographic preferences when spelling PWs having several different acceptable pronunciations. Finally, AD patients and controls produced similar types of errors when spelling real words. Dementia severity was related to the overall accuracy, but not to the pattern, of spelling responses. It is suggested that the decline in response accuracy in cognitively demanding writing tasks in patients with more advanced dementia is most likely due to semantic impairment and impairments of nonlinguistic functions of attention, executive control and praxis, rather than to a disturbance within language specific processes.