Age-Related Changes of Amplitude Modulation Representations in the Auditory System and Behavioral Temporal Perception
Abstract
Age-related changes of temporal processing, which result in compromised speech and complex sound recognition, are common features of presbycusis, aka age-related hearing loss. Human speech, music and biological relevant sounds are dynamic in nature and contain complex modulations in amplitude and frequency. Evidences of previous findings showed that central auditory processing of temporally modulated sounds, such as amplitude and frequency modulation (AM and FM), declines with age . However, there is a lack of evidence on age-related changes of temporal representations at the peripheral level as well as the corresponding declination in behavioral temporal perception. There is also an intrinsic limitation to compare central temporal processing accurately in aging due to confounding effects from the degradation of the auditory periphery. To solve these issues, age-related changes of temporal representations of AM were characterized at the peripheral level and with more stringent conditions (e.g. at equivalent neural activation and in noisy backgrounds) at the central level. The resultant consequences of age-related deficits of temporal processing as expressed in the behavior were investigated as well. Taken together, the results of this study would aid in identifying the source(s) of age-related auditory deficits as well as the correlation of temporal processing with behavioral temporal perception. Examination of cochlear mechanics induced by AM stimulus using distortion product otoacoustic emissions (DPOAEs) revealed that age-related changes in cochlear AM representations are associated with reduced endocochlear potential and decreased prestin activity although hair cell bundle function is normal. DPOAEs evoked by a combination of pure tone and AM tone at various AM depths could be used as an estimate for cochlear AM representations. When neural activation was matched at the peripheral or central level, AM processing, as assessed by envelope-following responses (EFRs), in high passed noise suggested that young animals were able to segregate modulated noise from the target AM tone at lower noise intensities and maintain dual AM representations. In contrast, aged animals were able to detect the presence of modulated noise at lower noise intensities but could not segregate the two AM sources until noise level increased above the neural phase-locking thresholds. Behavioral AM frequency discrimination abilities, as measured using prepulse inhibition of the acoustic startle responses, were highly reduced in aging when temporal salience of AM depth or AM frequency difference decreased. Comparison of behavioral and neurophysiological responses to similar AM stimuli unraveled that age-related decline of behavioral AM frequency discrimination performance is larger than age-related reduction of EFRs.
Degree
Ph.D.
Advisors
Bartlett, Purdue University.
Subject Area
Audiology|Biology|Neurosciences|Aging|Biomedical engineering
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