Spelling via semantics and phonology: exploring the effects of age, Alzheimer's disease, and primary semantic impairment.

Spelling performance across a common set of stimuli was examined in young adults, healthy older adults, individuals with early stage dementia of the Alzheimer's type (DAT), and four individuals with a primary semantic impairment (PSI). The stimuli included homophones and low-frequency sound-to-spelling consistent (i.e. words with more predictable spellings) and inconsistent words (i.e. words with less predictable spellings). The results indicate that when spelling homophonic words (spelling/pleIn/ as plane versus plain), younger adults and to a greater extent individuals with PSI placed relatively more emphasis on phonological information (i.e. spell the word based on sound-to-spelling principles) whereas healthy older adults and individuals with DAT placed relatively more emphasis on semantic information (i.e. spell the word based on the dominant usage). For non-homophonic words, large consistency effects (spelling plaid as plad) were observed for both individuals with DAT and individuals with PSI. It is proposed that the decrease in accuracy for inconsistent words has different bases in DAT and PSI. We propose that deficits in attentional control (i.e. selection) underlie performance in DAT whereas disruption of semantic representations underlies performance in PSI.