The Jaw-Hearing Dolphin: Preliminary Behavioral and Acoustical Evidence
Two decades ago, Norris (1964, 1968) proposed that the lower jaw of the dolphin was the primary pathway to the tympanoperiotic bone for returning acoustic signals during echolocation. Unlike that of terrestrial mammals, the lower jaw in odontocetes is hollow and filled with a fatty material that extends beyond the pan bones to attach to the tympanic bulla. This material has been found to contain lipids which contribute to its ability to transmit sound (Varanasi and Malins, 1971; 1972). Electrophysiological studies have indicated that acoustical stimuli presented to the lower jaw evoke significant responses in the auditory system of the dolphin (Bullock et al., 1968; McCormick et al., 1970; 1980). Bullock et al. (1968) further reported that foam rubber or paper placed over the lower jaw to block acoustical stimuli significantly attenuated responses. Several investigators have considered the jaw-hearing hypothesis and its possible role, at least in part, in the findings of their acoustical experiments with dolphins as well (Renaud and Popper, 1975; Au, Floyd, and Haun, 1978; Au and Moore, 1984). Other than a limited attempt to hinder a dolphin’s use of its lower jaw which remained inconclusive (Norris, 1974), what has lacked in the evaluation of this theory is behavioral and acoustical evidence gained from a living animal actively echolocating under controlled conditions.
KeywordsAcoustical Stimulus Echolocation Signal Acoustical Experiment Tympanic Bulla Cassette Tape Recorder
Unable to display preview. Download preview PDF.
- Brill, R.L., 1981, R.I.R. in use at the Brookfield Zoo: random and interrupted reinforcement redefined in perspective, in: “Proceedings of the Annual Conference of the International Marine Animal Trainers Association, 1981, Niagara Falls, New York,” J. Barry and R.L. Brill, eds., New England Aquarium, Boston.Google Scholar
- Bullock, T.H., Grinnell, A.D., Ikezono, E., Kameda, K., Katsuki, Y., Nomoto, M., Sato, O.,Suga, N., and, Yanigasawa, K., 1968, Electrophysiological studies of central auditory mechanisms in cetaceans, Z. Vergleich. Physiol., 59: 117–156.Google Scholar
- Green, D.M., and Swets, J.A., 1966, “Signal Detection Theory and Psychophysics,” Robt. E. Krieger Publishing Co., Huntington, New York.Google Scholar
- McCormick, J.G., Wever, E.G., Ridgway, S.H., and Palin, J., 1980, Sound reception in the dolphin ear as it relates to echolocation, in: “Animal Sonar Systems,” R.-G. Busnel and J.F. Fish, eds., Plenum Publishing Corp., New York.Google Scholar
- Norris, K.S., 1964, Some problems of echolocation in cetaceans, in: “Marine Bioacoustics,” W.N. Tavolga, ed., Pergamon Press, New York.Google Scholar
- Norris, K.S., 1968, The evolution of acoustic’-mechanisms in odontoncete cetaceans, in: “Evolution and Environment,” E.T. Drake, ed., Yale University Press, New Haven, Connecticut.Google Scholar
- Norris, K.S., 1974, “The Porpoise Watcher,” W.W. Norton and Co., Inc., New York.Google Scholar
- Renaud, D.L., and Popper, A.N., 1975, Sound localization by the bottlenose porpoise Tursiops truncatus, J. Acoust. Soc. Am., 63: 569–585.Google Scholar
- Schusterman, R.J., 1980, Behavioral methodology in echolocation by marine mammals, in: “Animal Sonar Systems,” R.-G. Busnel and J.F. Fish, eds., Plenum Publishing Corp., New York.Google Scholar
- Siegel, S., 1956, “Nonparametric Statistics for the Behavioral Sciences,” McGraw-Hill, New York.Google Scholar