Neural Correlates of Auditory Function and Training in Older Adults

Abstract

Older adults often report that they can hear what is being said, but that speech is unclear or distorted, especially when spoken rapidly or in background noise. These difficulties cannot be fully explained by the decrease in hearing thresholds that often accompanies aging. For these reasons, attention has increasingly focused on the impact of aging on central auditory processing of speech, and on the ways in which older adults access cognitive skills to compensate for the effects of hearing loss or reduced auditory processing.

The purpose of this is dissertation is to examine the neural processing underlying speech-in-noise perception deficits in older adults, and to assess the effects of auditory-based cognitive training on neural processing of speech in noise and associated perceptual and cognitive skills. Five studies were undertaken to explore the neural mechanisms contributing to successful speech-in-noise performance and the effects of aging and hearing loss on speech-evoked subcortical responses. The auditory brainstem response to complex sounds (cABR) was used to provide an estimate of the auditory system's ability to encode speech. The fundamental frequency, the neural correlate of pitch, is more robustly represented in the brainstem responses of older adults with good hearing in noise, compared to those with relatively poorer hearing in noise. In addition, the deleterious effects of background noise are increased in individuals who have trouble hearing in noise. The cABR is a better predictor of self-reported hearing-in-noise ability than typically used measures of hearing and speech-in-noise performance. In addition to brainstem processing, cognitive measures also play a big role in prediction of hearing in noise. The effects of aging and hearing loss can extend beyond reduced audibility. Two studies evaluated the effects of auditory-based cognitive training on subcortical measures of speech-in-noise processing and concomitant behavioral gains. After eight weeks of training, participants experienced improvements in speech-in-noise processing and in perceptual and cognitive function. These studies suggest an important role for the neural evaluation of auditory function in the clinical assessment and management of auditory dysfunctions. Importantly, impaired processing resulting from age or hearing loss can be partially reversed with training.