Effects of Normal Cognitive Aging on Spoken Word Frequency: Older Adults Exhibit Higher Function Word Frequency and Lower Content Word Frequency than Young Adults

Background Recent work indicates that word frequency (WF), broadly defined as an estimate of how often a given word is produced during spontaneous speech, has been shown to be a sensitive marker for conditions like mild cognitive impairment (MCI) and Alzheimer’s disease (AD). WF has been linked to cognitive declines observed in these groups. However, it is largely unknown how WF for distinct word classes change as part of normative cognitive aging, and to what extent factors like education and life experience may protect against age-related cognitive decline. Objective The current study examined WF and its association with cognitive test performance in older and younger adults. Higher WF values indicate the use of more common, higher frequently used words that are more readily retrieved from the lexicon, whereas lower WF values indicate the use of less common, lower frequency words. Methods Expository speech transcripts of 70 older and 130 younger adults were analyzed. Subject-level WF indices were computed for all words (AWs), content words (CWs) and function words (FWs). Between-group differences in WF and neuropsychological test performance were examined using independent samples t-tests and associations between WF and cognitive performance were evaluated with Pearson correlations. Follow-up analyses clarified the possible contribution of education. Results Higher average AW and CW frequency was observed in younger adults and higher AW frequency was associated with poorer performance on a test of mental reasoning (Cognitive Estimation Test). Though small, differences between age groups remained significant after accounting for education levels. Conclusion The current results show generally preserved WF in older adults and suggest that healthy cognitive aging and formal education do not drive the age-related changes in WF found in other studies. If replicated, such findings suggest that a shift from lower to higher frequency words in the spontaneous speech of older adults may be a marker of early neuropathological changes rather than normative cognitive aging and that the specific pattern may be influenced by sociocultural factors like language exposure and life experience. Future studies examining changes in lexical retrieval with advancing age will help clarify the impact of normative cognitive aging on WF indices and the extent to which analysis of spontaneous speech may help with early detection for conditions like MCI and AD.