Interaural time discrimination in the bottlenose dolphin

Abstract

Binaural hearing is the advantage of two ears over one. Localization studies with marine mammals have shown that acoustic localization underwater is mediated by the same binaural mechanisms used by other mammals in air. Dolphin echolocation abilities are enhanced by the use of two separate receivers. Au and Moore [J. Acoust. Soc. Am. 75, 255–262 (1984)] modeled the animal’s hearing system as a two-element array using receiving beam pattern measurements. The present study sought to measure the interaural phenomena of interaural time difference discrimination (ITD) and interaural intensity difference discrimination (IID). A dolphin was trained to accept contact hydrophones, attached by suction cups, to the outer surface of the lower jaw in the area of the pan-bone and to perform detection threshold experiments. Audiometric data at several frequencies indicate that the dolphin minimum threshold for pure tones may be 20 dB different when measured with jaw phones. The first behavioral measures of ITD and IID discrimination and for a cetacean have been obtained. ITD and IID for clicks trains of various frequencies, presented with interclick intervals simulating various echolocation target ranges were collected. This method of collecting audiometric data represents a new approach for assessing bearing capabilities in cetaceans.