Laser vibrometry measurements of acoustic coupling across alligator eardrums
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1
University of Maryland College Park, Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, United States
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2
University of Southern Denmark, Institute of Biology, Denmark
Physiological and anatomical studies have suggested that alligators have unique adaptations for spatial hearing. It has been hypothesized that directionality may be enhanced via the acoustic coupling of middle ear cavities, resulting in a pressure difference receiver (PDR) mechanism. Such coupling has been shown to generate directional pressure difference receiver effects in a number of other non-mammalian species; and anatomical evidence suggest that there maybe more than one potential pathway for interaural sound transmission in alligators. We have utilized laser vibrometry to record eardrum movement directly, and thereby measure the amplitude and phase gains afforded by sound transmission through the head of an anesthetized juvenile American alligator. We have also used free-field sound presentation to measure the directional sensitivity of eardrum vibration. By combining current eardrum vibration measurements with previous physiological, acoustic, and anatomical data we are able to provide a more complete picture of how these evolutionarily important low-frequency hearing animals localize sound. One kilohertz is an ethologically relevant frequency for these animals, because it is the best hearing frequency and a major component of juvenile American alligator vocalizations (Higgs et al., 2002, Campbell, 1973). Congruently, the alligator eardrum showed pronounced directionality around 1 kHz, where ipsi-contralateral differences are up to 10 dB. Interaural transmission shows a maximum around 1 kHz, so the directionality, measured in free-field, is likely produced by interaural coupling.
Acknowledgements
HSB was supported by NIH training grant to C-CEBH, UMCP.
References
D. M. Higgs et al., J Comp Physiol A 188, 217–223 (2002).
H. CAMPBELL, Zoologica-New York 58, 1–11 (1973).
Keywords:
alligator,
archosaurs,
directional,
Hearing,
Tympanum,
vibrometry
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Audition
Citation:
Bierman
HS,
Carr
CE and
Christensen-Dalsgaard
J
(2012). Laser vibrometry measurements of acoustic coupling across alligator eardrums.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00393
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Received:
01 May 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Hilary S Bierman, University of Maryland College Park, Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, College Park, United States, hilaryb@umd.edu