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Underwater hearing (of vertebrates). Human ear. The inner ear. Fish ears. Odontocete receiving system. “Acoustic fat” found ONLY here & melon. CT scan from Darlene Ketten. How do we test hearing?. Behavioral methods Animal trained Responds Go/no-go 2 alternative choice
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Odontocete receiving system “Acoustic fat” found ONLY here & melon CT scan from Darlene Ketten
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
Up-down staircase procedure 50% ‘catch trials’ (no signal present)
Envelope following response Supin et al.
ABR Magnitude
Behavioral vs. ABR Yuen et al. 2005
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
Fish hearing Tuna Damselfish Carp (goldfish) Salmon Cod Popper et al.
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
Human Cetacean hearing From: Au, 1993
Pinniped external ears Sea lion Elephant seal Harbor seal Kastak et al. 1999
Pinniped in-air hearing Kastak et al. 1999
Pinniped underwater hearing Kastak et al. 1999
Fur seal In air vs. underwater – pressure or intensity? Harbor seal Pressure – assumes hearing mechanism Intensity – corrects for acoustic properties of media. Energy flow measure Does not require knowledge of stimulus mechanism 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 Elephant seal
Hearing curves combined Sea lion Bottlenose dolphin Cod Catfish Harbor porpoise
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
Up to 40 tones were presented to the whale during a dive Ridgway, S. H. et al. J Exp Biol 2001;204:3829-3841
Increasing pressure (up to 300 m dives) Did not affect hearing Changed whistle spectra and intensity One whale only clicked at 300 m depth “Deep EAR” results
Diving and elephant seal hearing Kastak et al. 2001
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
TTS Finneran et al 2005
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
Signal effects on hearing • Received intensity (source level + range + environmental conditions) • Frequency • Duration • Timing (spacing between sounds)