Bright, Kathryn


Stoody, Tina M.

Committee Member

Weber, Jennifer E.


Audiology & Speech-Language Sciences


University of Northern Colorado

Type of Resources


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Greeley (Colo.)


University of Northern Colorado

Date Created





80 pages

Digital Origin

Born digital


A brainstem auditory evoked response (BAER) is an objective test that measures changes in voltage in the ongoing electroencephalogram (EEG) in response to the presentation of acoustic stimuli, and is observed as a waveform with a known series of peaks. While the gold standard for measuring hearing sensitivity in humans is behavioral testing during which the listener provides a behavioral response to a sound (e.g., raising a hand or pressing a button), objective testing allows clinicians to estimate behavioral hearing sensitivity when behavioral testing is not possible. Therefore, BAER testing has been used as a tool to measure hearing in various animal species. In humans, aging typically affects the brainstem auditory evoked response, producing waveforms with decreased amplitudes, wave V thresholds at higher stimulus intensities, and increased latency of wave V responses. The purpose of this study was to evaluate the effects of aging on the BAER in equines. The following research questions were investigated: Can brainstem auditory evoked responses be identified and replicated for older horses? If they can be identified, are there differences in response characteristics between young and old horses who have not participated in or been exposed to noisy situations in a convenience sample of horses? It was hypothesized that the older group of horses would exhibit poorer thresholds, poorer morphology, increased latencies, and a decrease in amplitude of waves compared to the younger group. Data were collected and analyzed from ten test subjects, five old (>20 years) and four young (<7 years) horses. Data obtained from one of the older horses was not included in the data analysis due to excessive noise from tooth grinding that obscured the waveforms. BAER testing was performed and waveforms were identified and replicated. Peak amplitudes, peak latencies, and thresholds were descriptively and statistically analyzed. There were no statistically significant differences between the two test groups. It is unclear why age-related differences were not observed. It is possible that what is considered age-related hearing loss (presbycusis) in humans, is the cumulative effect of noise, ototoxicity, and other environmental factors. It is also possible that the click stimulus did not elicit responses from the frequency range most sensitive to age- related changes in horses. Future research should explore using other stimuli, such as high-frequency tonebursts, to evaluate other frequency ranges, determine the feasibility of sedating subjects to reduce artifact, evaluate test-retest reliability of the brainstem auditory evoked response in horses, and include brainstem auditory evoked response testing on a group of horses with noise exposure to compare with the results from this study.

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