Consistency and regularity in past-tense verb generation in healthy ageing, Alzheimer's disease, and semantic dementia.

Older adults, individuals with dementia of the Alzheimer's type (DAT), and individuals with semantic dementia (SD) produced the past tense of verbs based on present-tense carrier sentences (e.g., Everyday I ding the bell. Yesterday I_____the bell). Both regularity (i.e., whether or not -ed is used for the past tense) and consistency (i.e., the degree to which verbs of similar orthography and phonology in the present tense have similar past tenses to the target) were manipulated. Participants received regular consistent (e.g., land-landed), regular inconsistent (e.g., weed-weeded), irregular consistent (e.g., sting-stung), and irregular inconsistent (e.g., light-lit) verbs. The dependent measures were overall accuracy rates and error rate types (e.g., regularizations, analogies, and other errors). Both consistency and regularity influenced performance. In addition, individuals with DAT showed a disproportionate deficit for inconsistent verbs associated with a high summed frequency of enemies, whereas SD individuals produced disproportionate breakdowns in performance on regular inconsistent, irregular consistent, and irregular inconsistent verbs. These results are consistent with the perspective that semantic/lexical processes are involved in processing the past tense of both irregular verbs and regular inconsistent verbs, and that attention is used to select appropriate responses and control inappropriate responses.