Poster C53, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall
How aging affects the neural basis of phonological and semantic neighborhood density
Michele T Diaz1, Victoria H. Gertel1, Hossein Karimi1, Sara B.W. Troutman1, Abigail L. Cosgrove1, Carla B. Fernandez1, Haoyun Zhang1;1Pennsylvania State University
Although many aspects of language remain stable with age, aging is 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 indicate age-related increases in retrieval difficulty. Moreover, prior work has suggested that these retrieval difficulties may be phonologically based. In contrast to language production, semantic aspects of language are relatively preserved: healthy older adults generally have larger and more diverse vocabularies and demonstrate comparable performance to younger adults on semantic tasks. Age differences in phonological processes, contrasted with the relative sparing of semantic processes, suggest a fundamental difference in the organization of these two abilities. In the present picture naming study, we investigated the influence of lexical factors (phonological and semantic neighborhood densities, PND & SND) on the neural basis of word retrieval across the lifespan (N=91, ages 20-75). Prior work has demonstrated that words with large phonological neighborhoods are produced faster, while words with large semantic neighborhoods are produced slower. However, the neural bases of these effects remain unknown. Behavioral results revealed that as PND increased, naming times decreased, and accuracies increased, ps < .001. In contrast, as SND increased, naming became more difficult, as reflected in increased naming times and decreased accuracies, ps < .001. Interestingly, we did not see a significant effect of age on RT, although the effect was trending in the expected direction, p = .07. Consistent with the behavioral analyses, fMRI analyses showed that decreasing PND was associated with increases in activation throughout the left hemisphere language network, as well as its right hemisphere homologues (e.g., bilateral superior temporal, inferior frontal, insula). As age increased, decreases in PND were associated with increases in activation in left superior temporal gyrus and left posterior middle temporal gyrus (MTG) – regions that are important for phonological encoding and retrieval. In contrast to our phonological findings, both increases and decreases in SND were associated with changes in activation. Increasing SND was associated with activation in bilateral lateral occipital cortex, suggesting increased visual competition. Decreasing SND was associated with activation in left orbital frontal gyrus, left middle frontal gyrus (MFG), and bilateral MTG – which suggests that weaker semantic neighborhoods engage both domain general cognitive control regions as well as semantic regions. Age effects showed that as SND decreased, reflecting sparser semantic networks, there were age-related increases in right middle and superior frontal gyri. Overall, these results suggest that increasing phonological selection demands engaged core language regions, and engagement of these phonological regions increased with age. While increasing semantic selection demands engaged both language-specific and domain general control regions, and that engagement of these domain general control regions increased with age.
Themes: Language Production, Phonology and Phonological Working Memory
Method: Functional Imaging