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The ear of lizards is highly directional. The directionality is generated by a simple principle: strong acoustical coupling of the eardrums through the large mouth cavity. Our laser vibrometry measurements show that the gecko ear is a two-input system with approximately 0 dB contralateral transmission gain in a 2 kHz frequency band. This transmission is boosted by resonances in the large, open tympanic cavities. Probably because of these resonances, the interaural delay is approximately three times larger than the arrival-time differences at the gekko eardrums. The directionality can be modelled by a simple three-impedance acoustical analog. Since already the ear is directional, the subsequent neural processing may be much simpler than in mammals, for example, where directionality is based on neural computation. Our neurophysiological experiments show that binaural comparison is based on contralateral inhibition with no apparent segregation of time and intensity processing. This simple computation generates a strongly directional lateralization that is sufficient to orient the animal, as shown by robot simulations.
3. maj 2007
<strong>Reverse engineering of the lizard ear</strong>