Underwater hearing (of vertebrates)

1. Underwater hearing (of vertebrates)

2. Human ear

3. The inner ear

4. Fish ears

5. Odontocete receiving system “Acoustic fat” found ONLY here & melon CT scan from Darlene Ketten

6. 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

7. Up-down staircase procedure 50% ‘catch trials’ (no signal present)

8. Envelope following response Supin et al.

9. Envelope following response ABR

10. ABR threshold calculation

11. ABR Magnitude

12. Behavioral vs. ABR Yuen et al. 2005

13. 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

14. Fish hearing Tuna Damselfish Carp (goldfish) Salmon Cod Popper et al.

15. 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

16. Human Cetacean hearing From: Au, 1993

17. Pinniped external ears Sea lion Elephant seal Harbor seal Kastak et al. 1999

18. Pinniped in-air hearing Kastak et al. 1999

19. Pinniped underwater hearing Kastak et al. 1999

20. 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

21. Hearing curves combined Sea lion Bottlenose dolphin Cod Catfish Harbor porpoise

22. 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

23. Up to 40 tones were presented to the whale during a dive Ridgway, S. H. et al. J Exp Biol 2001;204:3829-3841

24. Depth effects – Beluga whales

25. 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

26. Diving and elephant seal hearing Kastak et al. 2001

27. 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

28. TTS Finneran et al 2005

29. 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

30. Signal effects on hearing • Received intensity (source level + range + environmental conditions) • Frequency • Duration • Timing (spacing between sounds)