Anuran ears function as pressure difference receivers, and the amplitude and phase of tympanum vibrations are inherently directional, varying with sound incident angle. We quantified the nature of this directionality for Cope's gray treefrog, Hyla chrysoscelis. We presented subjects with pure tones, advertisement calls, and frequency-modulated sweeps to examine the influence of frequency, signal level, lung inflation, and sex on ear directionality. Interaural differences in the amplitude of tympanum vibrations were 1-4 dB greater than sound pressure differences adjacent to the two tympana, while interaural differences in the phase of tympanum vibration were similar to or smaller than those in sound phase. Directionality in the amplitude and phase of tympanum vibration were highly dependent on sound frequency, and directionality in amplitude varied slightly with signal level. Directionality in the amplitude and phase of tone- and call-evoked responses did not differ between sexes. Lung inflation strongly affected tympanum directionality over a narrow frequency range that, in females, included call frequencies. This study provides a foundation for further work on the biomechanics and neural mechanisms of spatial hearing in H. chrysoscelis, and lends valuable perspective to behavioral studies on the use of spatial information by this species and other frogs.
|Number of pages
|Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology
|Published - Apr 2014
Bibliographical noteFunding Information:
Acknowledgments We thank Sandra Tekmen and Jessica Ward for logistical support and for assistance in the lab, Marcos gridi-Papp for consultation on the development of our experimental methodology, and two anonymous reviewers for their helpful comments on an earlier version of this manuscript. All procedures followed the guide for the Care and Use of laboratory Animals and were approved by the University of Minnesota’s Institutional Animal Care and Use Committee (protocol #1103A97192) or the Danish national Animal experimentation board (protocol 2009/561-1645). This work was supported by a grant from the national Institute on Deafness and Other Communication Disorders (r01 DC009582). Katrina Schrode was supported by a national Institutes of Health Pre-doctoral Training grant (nIH T32 nS048944).
- Auditory periphery
- Eardrum vibrations
- Hyla chrysoscelis
- Lung inflation