Response consistency on a semantic memory task in persons with dementia of the Alzheimer type

The purpose of this investigation was to determine the test-retest response consistency rate on a semantic memory task in persons with dementia of the Alzheimer type (DAT). Ten mildly and 13 moderately impaired DAT subjects and 14 normal controls matched for age, years of education, and estimated IQ participated in this study. The Peabody Picture Vocabulary Test (PPVT) was administered twice to each subject with a 7-day intertest interval. The mild and moderate DAT subjects responded inconsistently to significantly more PPVT items than normal controls. When the effects of guessing were considered, moderate DAT subjects gave significantly more inconsistent PPVT responses than normal controls and mild DAT subjects showed a trend toward giving more inconsistent responses. These results substantiate the conclusion that the impairment of specific conceptual knowledge in DAT subjects cannot be reliably measured with a single administration of a semantic memory task such as the PPVT.