Animal Sonar Systems

Volume 28 of the series NATO Advanced Study Institutes Series pp 495-509

Peripheral Sound Processing in Odontocetes

  • Kenneth S. NorrisAffiliated withCoastal Marine Laboratory, University of California — Environmental Studies

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A decade ago two divergent theories describing peripheral sound processing in odontocetes had been formulated. Their differences were unresolved. One view held that sounds were generated in the larynx, radiated through the soft tissue of the throat or transmitted up through the skull and rostrum. Reception was thought restricted to the region of the external auditory meatus, a pinhole in most odontocetes. Sounds gathered at this region were thought to be transmitted to the middle ear via the narrow and sometimes occluded external auditory canal and the tympanic ligament (Fraser and Purves, 1959; Purves, 1966). The second view suggested quite radical modification of both sound reception and transmission paths. Sounds were envisioned as being produced by extra-laryngeal structures adjacent to the nasal passages in the forehead, and transmitted and transduced into the water via the fatty melon of the odontocete forehead, or through the mesorostral canal of the odontocete snout.