Hearing Loss in Harbor Seals: Differential Diagnoses of Conductive and Sensorineural Losses via Auditory Evoked Potentials (AEP), Otoacoustic Emissions (OAE), and Computerized Tomography (CT)

TitleHearing Loss in Harbor Seals: Differential Diagnoses of Conductive and Sensorineural Losses via Auditory Evoked Potentials (AEP), Otoacoustic Emissions (OAE), and Computerized Tomography (CT)
Publication TypeConference Paper
Year of Publication2011
AuthorsKetten, D. R., A. T. Mooney, R. C. Williams, K. Matassa, K. Patchett, J. J. Arruda, and S. R. Cramer
Conference Name19th Biennial Conference on the Biology of Marine Mammals
Pagination156
Date Published11/2011
PublisherSociety for Marine Mammology
Conference LocationTampa, FL
KeywordsAEP, auditory evoked potential, computerized tomography, ct, harbor seal, hearing loss, noise impacts, oae, otoacoustic emissions, phoca vitulina, pinniped
AbstractAs concerns for noise impacts continue, more species and individuals are being tested to determine hearing ranges and peak sensitivities. In employing these results, it must be considered that data, particularly from stranded wild animals, older individuals, or high noise areas, may reflect abnormal hearing. Case studies demonstrate pinnipeds sustain a wide range of conditions that may impair hearing.
Full TextAs concerns for noise impacts continue, more species and individuals are being tested to determine hearing ranges and peak sensitivities. In employing these results, it must be considered that data, particularly from stranded wild animals, older individuals, or high noise areas, may reflect abnormal hearing. Case studies demonstrate pinnipeds sustain a wide range of conditions that may impair hearing. Approximately 20 % of stranded seals have ear infections which if undetected and untreated may lead to septicemia. In this study, 5 harbor seals (Phoca vitulina) with overt or suspected infections were examined with CT, OAE, and AEP to determine the form, severity, and progress of pathologies and attendant hearing loss over time. CT scans were obtained prior to and during the hearing tests. For OAEs, the scans were used to assure that the ear canal remained open during testing and for measuring distance from the probe microphone tip to the eardrum. OAEs were obtained between 0.5-15 kHz. AEPs were obtained using surface electrodes with tones from 1-30 kHz. CT, AEP, and OAE results were assessed independently. Four animals had moderately elevated thresholds but normal brainstem responses, consistent with CT findings of conductive loss from occluded middle ears but normal inner ears. Differences in percent occlusion over time and across individuals were consistent with interaural threshold differences of 20-25 dB or more, progressing to a 55 dB deficit and retrograde loss in one case. A fifth animal with no overt infection had scans showing aggressive inner, middle, and external ear disease and no responses within 70 dB of normal response ranges. These techniques are useful for treatment and rehabilitation decisions, providing information on hearing losses that may be significant for foraging, navigation, and social interactions.