The use of language structure by demented patients in a visual search task.

Recent findings suggest that some components of semantic memory are spared by Alzheimer's disease. The present study used a visual-search task to determine whether knowledge of the sequential letter dependencies present in spelling remains intact in demented patients. The speed with which twenty Alzheimer patients, twenty young and twenty old controls searched an array of letters for a target was measured. Arrays varied in how closely they approximated English-spelling patterns (zero-order, and third-order approximations and actual words). Despite differing in their overall speed of response, normal and demented subjects were affected equally by the approximation to English of the stimuli (i.e., both searched words faster than low-order approximations). Thus, knowledge of the probability patterns of spelling appears to remain intact and accessible in the semantic memory of demented patients.