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Temporal resolution of the Florida manatee (Trichechus manatus latirostris) auditory system

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Auditory evoked potential (AEP) measurements of two Florida manatees (Trichechus manatus latirostris) were measured in response to amplitude modulated tones. The AEP measurements showed weak responses to test stimuli from 4 kHz to 40 kHz. The manatee modulation rate transfer function (MRTF) is maximally sensitive to 150 and 600 Hz amplitude modulation (AM) rates. The 600 Hz AM rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1,000–1,200 Hz). Audiograms estimated from the input–output functions of the EPs greatly underestimate behavioral hearing thresholds measured in two other manatees. This underestimation is probably due to the electrodes being located several centimeters from the brain.

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Auditory evoked potential


Envelope following response


Modulation rate transfer function


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We thank J. Warfield, and J. Leach for assistance with training and data collection. We appreciate the assistance of the manatee care interns, B. Jarvis, A. Breault, and L. Gilbert. We thank S. Rommel for discussions on manatee ear and brain anatomy. Research was supported by funding from the Florida Fish and Wildlife Conservation Commission, University of South Florida, Peg Scripps Buzzelli Endowed Chair in Psychology at New College of Florida, Mote Marine Laboratory and Aquarium, and Walt Disney Animal Programs. This research was conducted with the permission of the U.S. Fish and Wildlife Service, Permit Number: MA837923-4. The experiments comply with the "Principles of animal care", publication No. 86-23, revised 1985 of the National Institute of Health, and also with the current laws of the US.

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Correspondence to David A. Mann.

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Mann, D.A., Colbert, D.E., Gaspard, J.C. et al. Temporal resolution of the Florida manatee (Trichechus manatus latirostris) auditory system. J Comp Physiol A 191, 903–908 (2005).

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