Poster D39, Friday, August 17, 4:45 – 6:30 pm, Room 2000AB
The neural basis of phonological and semantic neighborhood density
Michele T. Diaz1, Hossein Karimi1, Anna Eppes1, Victoria Gertel1, Sara Winter1;1The Pennsylvania State University
There is considerable evidence that aging has a substantial negative effect on language production. One of older adults’ most frequent, frustrating, and embarrassing cognitive problems is word retrieval difficulty. Consistent with these reports, older adults endure more tip-of-the-tongue states than younger adults, and during TOT states older adults report less phonological information and fewer alternative words compared to younger adults, consistent with a phonologically based deficit as the underlying causal mechanism of these retrieval deficits. Moreover, other indices of language production also demonstrate poorer performance for older compared to younger adults: aging is associated with decreased speed and accuracy in naming objects, increased errors in spoken and written production, and more pauses and fillers in speech, which indicate age-related increased retrieval difficulty. In contrast to language production, other aspects of language are largely preserved with age. Healthy older adults generally have larger and more diverse vocabularies and demonstrate comparable performance to younger adults in making word associations and semantic judgments. Age differences in phonological processes, contrasted with the relative sparing of semantic processes, suggest a fundamental difference in the cognitive organization of these two abilities. While word retrieval failures reflect a common aspect of aging that affects the vast majority of older individuals, the neural bases of language production in healthy aging has received little attention. Results from our lab have shown significant age-related decline and weaker brain-behavior links underlying phonological aspects of language production. However, the specific aspects of phonological processing that contribute to these retrieval difficulties remains unknown. In the present study, we investigated the influence of lexical factors (phonological and semantic neighborhood density) on the neural basis of word retrieval, with a picture naming task. Prior work has demonstrated that words with larger phonological neighborhoods are produced faster, and the opposite trend has been observed for words with large semantic neighborhoods, particularly for words with salient competitors. However, the neural bases of these effects remain unknown. Preliminary results from an fMRI experiment (N=9), show that naming pictures elicited activation in typical language regions including left inferior frontal gyrus, posterior inferior temporal gyrus, bilateral precentral gyri, and left dorsal medial prefrontal cortex, as well as posterior visual processing regions. Decreases in phonological neighborhood density were associated with increases in activation in bilateral posterior middle temporal gyri, which have been implicated in lexical and phonological selection. In contrast, increases in semantic neighborhood density were associated with increases in activation in bilateral inferior frontal gyrus, and right frontal pole – regions that have previously been associated with semantic selection (LIFG) and general cognitive control (right frontal). These preliminary results suggest that increasing phonological selection demands engage core language regions, and that increasing semantic selection demands engage both language-specific and domain general control regions.
Topic Area: Meaning: Lexical Semantics