On-line lexical processing in AD and MCI: An early measure of cognitive impairment?

The present study examines on-line processing of mass nouns (e.g. honey), count nouns (e.g. table) and dual (metonymic) nouns (e.g. chicken) in healthy elderly controls with no evidence of cognitive impairment, patients suffering from probable Alzheimer's disease (pAD), and patients diagnosed with mild cognitive impairment (MCI). Participants performed a lexical decision task using a go/no-go paradigm, where they responded to words but not non-words. Within-group comparisons revealed that elderly controls manifested longer reaction times to mass nouns and count nouns than to dual nouns, while pAD and MCI patients manifested longer latencies to mass nouns, but no significant difference between count and dual nouns. The way in which lexicosemantic knowledge breaks down in the case of memory impairment is discussed, and it is argued that breakdown in lexical representations may provide a sensitive early measure of cognitive impairment.