Mutual Information Analysis of Neural Representations of Speech in Noise in the Aging Midbrain
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Abstract
Younger adults with normal hearing can typically understand speech in the presence of a competing speaker without much effort. However, the ability to understand speech in challenging conditions deteriorates with age. Older adults, even with clinically normal hearing, typically have problems understanding speech in noise. Earlier auditory studies using the frequency following response (FFR), dominantly generated by the midbrain, have demonstrated age-related neural deficits when analyzed using traditional measures. Here we analyze speech- driven FFR, for speech masked by competing speech, using a mutual information paradigm, by estimating the amount of stimulus information contained in the FFR. Our results show first a wide-band informational loss in both amplitude and phase of FFR associated with aging. Second, the loss of information is more severe in higher frequency bands (several hundred Hz) in older listeners. Third, the information decreases as noise level increases for both age groups, but older adults benefit when the background speech is changed from meaningful (talker speaking a language that they can comprehend, such as English) to meaningless (talker speaking a language that they cannot comprehend, such as Dutch), while younger do not. The results reveal a clear foreground informational loss in midbrain associated with aging, which is more severe when the background noise is meaningful to them than when it is meaningless. Download Poster