QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online March 14, 2005
Journal of Experimental Biology 208, 1209-1217 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01511

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Christensen-Dalsgaard, J. Articles by Manley, G. A. Search for Related Content PubMed PubMed Citation Articles by Christensen-Dalsgaard, J. Articles by Manley, G. A.

Directionality of the lizard ear

Jakob Christensen-Dalsgaard^1,* and Geoffrey A. Manley²

¹ Center for Sound Communication, SDU Odense University, Campusvej 55, DK-5230 Odense M, Denmark
² Lehrstuhl für Zoologie, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany

^* Author for correspondence (e-mail: JCD{at}biology.sdu.dk)

Accepted 26 January 2005

Lizards have highly sensitive ears, but most lizard heads are small (1-2 cm in diameter) compared to the wavelengths of sound of frequencies to which they are most sensitive (1-4 kHz, wavelengths 34-8.5 cm). Therefore, the main cues to sound direction that mammals use - binaural time and intensity cues due to arrival-time differences and sound shadowing by the head - will be very small in lizards.

The present work shows that acoustical coupling of the two eardrums in lizards produces the largest directionality of any terrestrial vertebrate ear studied. Laser vibrometric studies of tympanic motion show pronounced directionality within a 1.8-2.4 kHz frequency band around the best frequency of hearing, caused by the interference of ipsi- and contralateral inputs. The results correspond qualitatively to the response of a simple middle ear model, assuming coupling of the tympana through a central cavity. Furthermore, observed directional responses are markedly asymmetrical, with a steep gradient of up to 50-fold (34 dB) response differences between ipsi- and contralateral frontal angles. Therefore, the directionality is easily exploitable by simple binaural subtraction in the brain. Lizard ears are the clearest vertebrate examples of directionality generated by tympanic coupling.

Key words: hearing, auditory, eardrum, tympanum, reptile, lizard, frog, bird