Decline in homophone spelling associated with loss of semantic influence on spelling in Alzheimer's disease

Abstract

The homophone spellings of 20 subjects with Alzheimer′s disease (AD) and mild dementia were compared to those of matched normal controls. Both groups were tested once (Time 1) and then again 9 months to 1 year later (Time 2). At Time 1, AD subjects misspelled more homophones than the control group and the discrepancy between the two groups′ performances significantly increased by Time 2. Two types of errors were tabulated: homophone confusions (i.e. an inappropriate yet correctly spelled homophone given the context, such as spelling doe, given the context "bake the bread dough") and other spelling errors (e.g. doue, dogh). The relationship between homophone confusions and confrontation naming increased from Time 1 to Time 2. In contrast, the relationship between the number of spelling errors (that were not homophone confusions) and confrontation naming performance was not significant at Time 2. One subgroup of 3 subjects showed an increase in homophone confusions and confrontational naming errors and not more spelling errors. Another subgroup of 4 subjects showed neither an increase in homophone confusions nor in confrontational naming errors, but did show an increase in spelling errors. Based on these results, we suggest that homophone confusions are primarily due to impairment of semantic access to a functional orthographic output lexicon. Other spelling errors may reflect post-linguistic spelling deficits without a significant change in the use of semantic input for spelling homophones.