Meeting Abstract

P2.152  Thursday, Jan. 5  Evidence for a pressure difference receiver system in alligator sound localization. BIERMAN, H.S.*; YOUNG, B.A.; THORTON, J.L.; JONES, H.G.; KOKA, K.; CARR, C.E.; TOLLIN, D.J.; University of Maryland, College Park; University of Massachusetts, Lowell; University of Colorado Medical School, Aurora; University of Colorado Medical School, Aurora; University of Colorado Medical School, Aurora; University of Maryland, College Park; University of Colorado Medical School, Aurora hilaryb@umd.edu

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. We have therefore measured the acoustic cues available to the animal, and re-examined the skull anatomy of the juvenile American alligator. Directional transfer functions, the directional component of the head-related transfer function, were measured for 4 specimens. Interaural differences in time and level, as well as monaural spectral shape cues, calculated from these measurements, showed no evidence for enhanced cues generated by the animal’s morphology. Behaving similarly to a spherical model, results refute the null hypothesis that physiological results are accounted for by cues generated by the passive transformation of sound pressures about the animal’s head and body. The PDR hypothesis is instead supported by anatomical data verifying the presence of continuous dorsal and ventral pathways that connect the middle ear cavities. A muscular flap separating the Eustachian tube from the pharynx further suggests that these animals may have some control over transmission through the ventral pathway.