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Phonological neighborhood density effects in prefrontal cortex when listening to speech in noise
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Mel Mallard1, Chad S. Rogers2, Michael S. Jones1, Sarah McConkey1, Brent Spehar1, Kristin J. Van Engen1, Mitchell S. Sommers1, Jonathan E. Peelle3; 1Washington University in St. Louis, 2Union College, 3Northeastern University
Phonological neighborhood density—the number of words that sound similar to a target word—has long been considered in the context of spoken word recognition. However, the neural mechanisms through which listeners deal with increased competition are unclear. Some studies suggest neighborhood density effects are present in the temporal lobe, potentially relating to representations of acoustic features in competing words. Other studies suggest frontally-mediated mechanisms to handle ambiguity and resolve conflicts. Furthermore, how such processes might change in the context of normal aging are unclear, and of particular importance given older adults’ challenges understanding speech in noise. We conducted an fMRI study of a speech-repetition task in which we presented single spoken words in background noise to both young and older adults. Words varied in lexical competition demands, being selected to have either few neighbors (i.e., from a sparse phonological neighborhood, low competition) or many neighbors (i.e., from a dense phonological neighborhood, high competition). Participants were both young (n = 46; aged 19-30 years) and older (n = 30; aged 65-81 years) adults. To measure recognition accuracy, each trial was scored as either a correct or incorrect repetition. Accuracy was generally good (M = .81, SD = .12), and we restricted further analyses to correct responses only. As expected, at the whole brain level, spoken word recognition in noise was associated with activity in the left and right superior temporal gyrus. Supporting our hypothesis about DLPFC involvement in spoken word recognition, a region near the left inferior frontal sulcus showed a significant density effect, with Dense words eliciting more activity than Sparse words. To further characterize this effect, we extracted parameter estimates from each participant. Notably, the density effect did not significantly differ by age [t(72.4) = 0.87, p = .387, d = -0.20] and was not significantly correlated with hearing ability (better-ear pure-tone-average) in either the younger [r(44) = -.18] or older [r(28) = .10] group. These findings support a role for DLPFC in resolving lexical competition during spoken word recognition. Interestingly, DLPFC involvement was not related to either age or hearing sensitivity, suggesting a degree of stability in the neural systems underlying spoken word recognition outside the temporal lobe.
Topic Areas: Speech Perception, Control, Selection, and Executive Processes