Download - Underwater hearing (of vertebrates)
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Underwater hearing (of vertebrates)
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The inner ear
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Fish ears
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Odontocete receiving system
CT scan from Darlene Ketten
“Acoustic fat” found ONLY here & melon
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How do we test hearing?• Behavioral methods
– Animal trained– Responds
• Go/no-go• 2 alternative choice
• Auditory brainstem response– No training required– Record firing of auditory cortex
• Usually test pure tones• Occasionally test pulses
– Thresholds much lower for pulsed sounds than pure tones
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Up-down staircase procedure50% ‘catch trials’ (no signal present)
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Envelope following response
Supin et al.
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Envelope following response ABR
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ABR threshold calculation
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ABR
Mag
nitu
de
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Behavioral vs. ABR
Yuen et al. 2005
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Behavioral vs. ABR
• Behavioral– Requires months to train, months to test– Usually only 1 subject
• ABR– Requires no training, rapid testing
• Can be used to test for transient effects
– Can be done on more species e.g. stranded animals, catch and release animals
• Both require placement of a threshold that varies with conditions
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Fish hearing
Carp (goldfish)
Cod
Salmon
Damselfish
Tuna
Popper et al.
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3 types of fish ears• General fish
– No hearing specialization– 100-1,000 Hz– Best hearing 100-400 Hz
• Specialized hearing– Goldfish, catfish, etc.– 100-3,000 Hz– Best hearing 300-1,000 Hz
• High frequency adaptations– Clupeids (herring, shad, menhaden, sardine, anchovy)– Swimbladder morphology facilitates broad frequency hearing
range– 1-200,000+ Hz
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Cetacean hearing
Human
From: Au, 1993
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Pinniped external ears
Elephant seal Harbor seal Sea lion
Kastak et al. 1999
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Pinniped in-air hearing
Kastak et al. 1999
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Pinniped underwater hearing
Kastak et al. 1999
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In air vs. underwater – pressure or intensity?
Phocids (true seals) generally hear equally well in air and underwater – amphibious
Elephant seal – a deep diver hears better underwater (bone conduction in air)
Fur seals hear better in air – primarily terrestrial socialization and mating
Fur seal
Pressure – assumes hearing mechanismIntensity – corrects for acoustic properties of media. Energy flow measureDoes not require knowledge of stimulus mechanism
Elephant seal
Harbor seal
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Hearing curves combined
Bottlenose dolphinCod
Sea lion
Catfish
Harbor porpoise
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Project “Deep EAR”
• Human hearing attenuates with increasing pressure (chamber experiments)
• Beluga whales (a dolphin species) experience large pressure increases with diving
• Effects on whistling and hearing in free-swimming animals
Ridgway, S. H. et al. J Exp Biol 2001;204:3829-3841
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Ridgway, S. H. et al. J Exp Biol 2001;204:3829-3841
Up to 40 tones were presented to the whale during a dive
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Depth effects – Beluga whales
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“Deep EAR” results
• Increasing pressure (up to 300 m dives)
• Did not affect hearing• Changed whistle
spectra and intensity• One whale only
clicked at 300 m depth
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Diving and elephant seal hearing
Kastak et al. 2001
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Temporary threshold shifts
• Aural fatigue• Hearing threshold increased• Recovery follows with varying time course
(minutes – weeks)• Experiments in chinchillas and humans
have shown the relationship between TTS and PTS (permanent threshold shifts)
• Good predictor of auditory damage
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TTS
Finneran et al 2005
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Temporary threshold shifts
• Longer exposures to quieter sounds have the same effect as shorter exposures to louder sounds
• Exposure intensity usually relative to hearing threshold except for impulsive sounds
• The total exposure energy of the sound to which an animal is exposed important
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Signal effects on hearing
• Received intensity (source level + range + environmental conditions)
• Frequency• Duration• Timing (spacing between sounds)