Neuroanatomical characteristics and speech perception in noise in older adults

Previous research has attributed older adults' difficulty with perceiving speech in noise to peripheral hearing loss. However, recent studies have suggested a more complex picture and implicate the central nervous system in sensation and sensory deficits. This study examines the relationship between the neuroanatomical structure of cognitive brain regions and the ability to perceive speech in noise in older adults. In particular, the neuroanatomical characteristics of the left ventral and dorsal prefrontal cortex (PFC) are considered relative to standard measures of hearing in noise.

The participants were 15 older and 14 younger right-handed native speakers of American English who had no neurologic deficits and scored better than normal on standardized cognitive tests. We measured the participants' peripheral hearing ability and their ability to perceive speech in noise using established tests. Anatomical magnetic resonance images were taken and analyzed to extract regional volumes and thicknesses of several key neuroanatomical structures.

Younger adults had better hearing sensitivity and better speech perception in noise ability than older adults. For the older adults only, the volume of the left pars triangularis and the cortical thickness of the left superior frontal gyrus were significant predictors of performance on the speech in noise test.

These findings suggest that, in addition to peripheral structures, the central nervous system also contributes to the ability to perceive speech in noise. In older adults, a decline in the relative volume and cortical thickness of the PFC during aging can therefore be a factor in a declining ability to perceive speech in a naturalistic environment. These findings are consistent with the decline-compensation hypothesis, which states that a decline in sensory processing caused by cognitive aging can be accompanied by an increase in the recruitment of more general cognitive areas as a means of compensation. We found that a larger PFC volume may compensate for declining peripheral hearing. Clinically, recognizing the contribution of the cerebral cortex expands treatment possibilities for hearing loss in older adults beyond peripheral hearing aids to include strategies for improving cognitive function. We conclude by considering several mechanisms by which the PFC may facilitate speech perception in noise, including inhibitory control, attention, cross-modal compensation, word prediction and phonological working memory, although no definitive conclusion can be drawn.