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underwater audiogram of the West Indian manatee (Trichechus manatus latirostris)
Title
The underwater audiogram of the West Indian manatee (Trichechus manatus latirostris).
Creator
Gerstein, Edmund Roy, Florida Atlantic University, Salmon, Michael
Abstract/Description
The hearing abilities of two adult manatees were tested using a forced two-choice paradigm and an up/down staircase psychometric technique. Prior to this research, no hearing tests or audiograms had been measured for any Sirenian species. This test was also the first controlled underwater infrasonic hearing test conducted on any marine mammal. The audiogram demonstrated a wider range of hearing (0.5 to 38 kHz) and greater sensitivity (50 to 102 dB re:1muPa) throughout this range than had...
Show moreThe hearing abilities of two adult manatees were tested using a forced two-choice paradigm and an up/down staircase psychometric technique. Prior to this research, no hearing tests or audiograms had been measured for any Sirenian species. This test was also the first controlled underwater infrasonic hearing test conducted on any marine mammal. The audiogram demonstrated a wider range of hearing (0.5 to 38 kHz) and greater sensitivity (50 to 102 dB re:1muPa) throughout this range than had previously been suggested by averaged evoked potential and anatomical studies. The audiogram was a typical U-shaped mammalian hearing curve and was compared with other marine mammal underwater audiograms. Both manatees were most sensitive to frequencies between 12-18 kHz at 50-54 dB. The manatees' hearing sensitivity dropped more than 20 dB per octave below 1600 Hz. This higher frequency sensitivity may have evolved as an adaptation to a shallow water existence where low frequency sound propagation is limited. Limited hearing sensitivity at lower frequencies may be a contributing factor to the manatees' vulnerability to boat collisions.
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Date Issued
1995
PURL
http://purl.flvc.org/fcla/dt/15192
Subject Headings
West Indian manatee, Manatees--Florida, Manatees--Sense organs, Audiometry, Hearing levels
Format
Document (PDF)
Psychoacoustic evaluations of the West Indian manatee (Trichechus manatus latirostis)
Title
Psychoacoustic evaluations of the West Indian manatee (Trichechus manatus latirostis).
Creator
Gerstein, Edmund Roy, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Psychology
Abstract/Description
Psychoacoustic procedures were used to measure the heating thresholds of captive West Indian manatees under simultaneous masking conditions. Auditory detection thresholds of pulsed and non- pulsed pure tones, and complex sounds were measured against continuous white noise backgrounds through a series of forced-choice paradigms. Auditory thresholds as a function of signal intensity, center frequency, pulse repetition, spectral characteristics and bandwidth were measured. Resulting critical...
Show morePsychoacoustic procedures were used to measure the heating thresholds of captive West Indian manatees under simultaneous masking conditions. Auditory detection thresholds of pulsed and non- pulsed pure tones, and complex sounds were measured against continuous white noise backgrounds through a series of forced-choice paradigms. Auditory thresholds as a function of signal intensity, center frequency, pulse repetition, spectral characteristics and bandwidth were measured. Resulting critical signal-to-noise ratios for pure tone measurements suggest manatees have relatively acute frequency filtering abilities compared with humans and other marine mammals. Signal characteristics such as repetition rate along with amplitude and frequency modulation may lower detection thresholds by providing temporal contrasts against aperiodic background noise. Thresholds for frequency modulated bandlimited signals were measured near or below background noise levels. Threshold tests using broadband signals, including a species specific call and samples of boat noise suggest that loudness summation across critical bands, as well as modulation of signals, can reduce the effects of masking observed with pure tones. To test a manatee's ability to localize sound sources in relation to its position in the water, a forced-choice egocentric (orientation) paradigm was used. The manatee demonstrated equal localization of sounds originating from the left or right side. While accuracy improved with higher frequencies the manatee demonstrated good overall localization of both low and higher frequency sounds, suggesting it may utilize both time of arrival cues and intensity difference cues for localizing brief sounds. The psychoacoustic data reveal some hearing abilities unique to manatees, as well as hearing phenomena similar to those observed among mammals and other vertebrates species. Manatees are well adapted for hearing and locating high frequency sounds in noisy shallow water habitats where physical boundary and near surface phenomena such as the Lloyd Mirror Effect can impede the propagation of low frequencies. Narrow critical bands and selective perception of pulsed signals may be adaptations for detecting species-specific vocalizations. Results indicate manatees can not effectively detect the low frequency sounds of approaching boats from safe enough distances to avoid collisions in the wild.
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Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/12601
Subject Headings
Psychology, Psychobiology, Biology, Zoology, Agriculture, Fisheries and Aquaculture
Format
Document (PDF)