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The neural basis of phonological neighborhood density and lexical frequency across adulthood
Poster Session D, Saturday, October 26, 10:30 am - 12:00 pm, Great Hall 3 and 4
Michele Diaz1, Abigail Cosgrove1, Kathryn Walters1, Jie Yan1, Haoyun Zhang2; 1Penn State University, 2University of Macao
Although many aspects of language remain stable with age, aging is often associated with declines in language production. For example, compared to younger adults, older adults experience more tip-of-the-tongue states, show decreased speed and accuracy in naming objects, increased errors in spoken and written production, and more pauses and fillers in speech, all of which suggest age-related increases in retrieval difficulty. Although these behavioral effects are commonly observed, the mechanisms underlying age-related speech disfluencies is less understood. Prior work has demonstrated that words with small phonological neighborhoods and words that have a lower lexical frequency are produced more slowly by adults of all ages. Moreover, although older adults’ neural sensitivity to phonological and semantic features is stable across adulthood (Diaz et al., 2021; 2022), older adults may be particularly vulnerable to retrieval deficits with words that have particular characteristics such as sparse phonological neighborhoods or low lexical frequency (Gertel et al., 2020). Here we examined the combined effects of these lexical factors with functional Magnetic Resonance Imaging (fMRI). We used overt picture naming and manipulated the phonological neighborhood density (PND) and lexical frequency of the pictures to be named (N = 91, ages 20 - 89). Behaviorally, we found that adults of all ages were sensitive to lexical frequency and PND. In addition, increases in age were associated with naming pictures more slowly and less accurately. There were also Age x Frequency and Age x PND interactions such that increases in age were associated with slower and less accurate naming primarily when naming pictures with low frequency and PND. In terms of fMRI results we observed age-related increases in activation to picture naming in general, largely outside of typical language regions. We also observed an Age x PND x Frequency interaction, where older adults elicited less activation to the PND x Frequency interaction compared with younger adults in bilateral Inferior Frontal Gyrus and Insula, as well as right Superior Temporal Gyrus. The neuroimaging findings suggest that picture naming is associated with both neural dedifferentiation, as well as under recruitment of language specific regions.
Topic Areas: Language Production, Meaning: Lexical Semantics