Dolphin Cognition and Behavior: A Comparative Approach

By Ronald J. Schusterman; Jeanette A. Thomas et al. | Go to book overview
discrimination experiment ( Evans & Powell, 1967). Similar results were obtained from divers and porpoises for this particular set of targets and conditions. For the divers to make their target discrimination it was necessary to scan the targets by moving their heads if they did not they had difficulty in making choices.Other experiments have been conducted using human listeners and time- stretched echoes ( Au & Martin, 1983; Martin & Au, 1983). In these experiments echoes from targets ensonified with dolphin-like signals were digitized and played back at slower rates to the subjects. No scanning was involved in these measurements. They found that, under controlled laboratory conditions, humans had discrimination scores about as good as dolphins under less controlled conditions.
Important Areas For Future Work
1. The actual operation of the sound source and sonar beam generation is not understood. Measurements using velocity detectors instead of pressure transducers in the near-field would be helpful. Also, measuring changes in the shape of the nasal sacs might help clarify their role in sound production. When the "state of the art" is more advanced, pulse interference laser holography could be a powerful tool to study melon and other displacements during phonations.
2. Experiments using human listeners and electronically transformed echoes are a useful method of studying echolocation and should be continued. The importance of target scanning needs to be determined.
3. Floyd ( 1980) suggestion of using "electronic phantom" targets to test various theories is an extremely promising approach. In this type of experiment echoes are produced electronically and projected back to the dolphin in response to its own outgoing sonar pulses instead of using physical targets which simply reflect the outgoing signal. This approach allows the experimenter to check responses to specific changes in the echo.

REFERENCES

Altes R. A. ( 1973). A theory for animal echolocation and its application to ultrasonics. Ultrasonics Symposium Proceedings, IEEE Cat. No. 73 CHO 807-8 SU, 67-72.

Altes R. A. ( 1980). "Models for echolocation". In R. -G. Busnel & J. F. Fish (Eds.), Animal sonar systems (pp. 625-671). New York: Plenum Press.

Altes R. A., Evans W. E., & Johnson C. S. ( 1975). "Cetacean echolocation signals and a new model for the human glottal pulse". Journal of the Acoustical Society of America, 57, 1221-1224.

Anderson V. C. ( 1950). "Sound scattering from a fluid sphere". Journal of the Acoustical Society of America, 22, 426-31.

Au W. W. L. ( 1980). "Echolocation signals of the Atlantic bottlenose dolphin (Tursiops truncatus) in open waters". In R. -G. Busnell & J. F. Fish (Eds.), Animal sonar systems (pp. 251-282). New York: Plenum Press.

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