Phonological blocking during picture naming in dementia of the Alzheimer type.

Individuals with dementia of the Alzheimer type (DAT; n = 53, ages 55-91), healthy older adults (n = 75, ages 59-91), and younger adults (n = 24, ages 18-24) performed a word-primed picture-naming task. Word primes were neutral (ready), semantically or phonologically related, or unrelated to the correct picture name. AH groups produced equivalent unrelated-word interference and semantic priming effects in response latencies. However, analysis of errors revealed a DAT-related increase of phonological blocking. The results suggest that picture-naming errors in DAT are due, at least in part, to a breakdown in access to phonological representations of object names as a consequence of reduced inhibitory control over other highly active alternatives.