The Word-Frequency Mirror Effect in Young, Old, and Early-Stage Alzheimer's Disease: Evidence for Two Processes in Episodic Recognition Performance

Two experiments address the nature of the word-frequency mirror effect in episodic recognition performance and the underlying cognitive changes that occur in both healthy aging and in early-stage Dementia of the Alzheimer's Type (DAT). In Experiment 1, five groups of participants (young, healthy old, healthy old-old, very mildly demented individuals, and mildly demented individuals) studied lists of high- and low-frequency words and were given a yes/no episodic recognition test. The results indicated that there was a dramatic decrease in hit rate for low-frequency words across age and DAT, but no decrease for high-frequency words, thereby eliminating the low-frequency advantage typically found in recognition performance for the DAT individuals. For the distractor items, there was a clear advantage in rejecting low-frequency words compared to high-frequency words, and the size of this advantage was constant across groups of participants. This between-group pattern was replicated in a second experiment, in which only young adults were required to respond either under short or long response deadlines. The results are discussed with respect to an attentional control framework in which cognitively impaired groups of participants, and young adults at a short response deadline, rely more on baseline familiarity processes than on recollection-based processes. Discussion focuses on the nature of the recollection- and familiarity-based processes.