Memory, aging, and Alzheimer Disease

Abstract

"Levels of processing" and "dual-store" models were used to examine memory in persons with mild to moderate senile dementia of the Alzheimer type (SDAT) and carefully matched controls free of neurological impairment. Methods of testing included free and cued recall, and recognition memory for lists of words learned under conditions which ranged from free through phonemic (letter, rhyme) to three semantic conditions (object, praxic and objectpraxic combined). The findings were as follows. First, although recalling fewer words under all conditions and test measures, the SDAT subjects produced a pattern of recall qualitatively similar to that of the controls for cued recall and recognition, but not for free recall where their semantic processing appeared differentially impaired. Second, within the SDAT group, the milder but not more impaired subjects freely recalled more words under one semantic (object) relative to a phonemic condition. Third, more words were recalled following a semantic (praxic) cue compared with a phonemic cue, a result which held for both groups as well as the most impaired SDAT subjects. Fourth, the SDAT free recall score in the combination procedure was lower than expected if the individual conditions were additive, as seemed the case for the controls. The findings suggested that the semantic memory system may be selectively vulnerable, and the degree of impairment to certain structures appears related to the degree of dementia. There was also modest indication of a deficiency in processing greater number of stimulus features and attributes. It was proposed that person’s with SDAT have difficulty gaining access to concepts in semantic memory. Regarding the dual-store model, primary (PM) and secondary (SM), and types of intrusion errors were examined. PM and SM measures appeared independent in both groups. (Abstract shortened)