Is action naming better preserved (than object naming) in Alzheimer's disease and why should we ask?

The present study compared object and action naming in patients with Alzheimer's dementia. We tested the hypothesis put forward in (some) previous studies that in Alzheimer's dementia the production of verbs, that is required in action naming, is better preserved than the production of nouns, that is required in object naming. The possible reason for the dissociation is that verbs are supported predominantly by frontal brain structures that may remain relatively better preserved in early Alzheimer's disease. Objects, on the other hand, are supported by temporal lobe structures that are affected early in the disease. An alternative hypothesis, which is supported by other studies, is that action naming is more impaired than object naming due to verbs being semantically more complex than nouns. In order to test these contrasting hypotheses, the present study used more stringent methodology than previous studies. We used a larger set of stimuli with carefully matched object and action items and we collected not only accuracy data but also naming latencies, a measure that is sensitive to even mild lexical retrieval problems. We compared the performance of 19 patients with mild to moderate Alzheimer's disease with that of 19 healthy age matched participants. We found that both the patients and the comparison group responded faster and made fewer errors on the object pictures than the action pictures. A qualitative analysis of the naming errors indicated that object and action naming pose different demands for the language system. The results overall suggest that the patients' performance is an exaggeration of the pattern present in the comparison participants.