HORIZONTAL ANGULAR DISCRIMINATION BY AN ECHOLOCATING BOTTLENOSE DOLPHIN TURSIOPS TRUNCATUS |
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Authors: | BRIAN K. BRANSTETTER SONJA J. MEVISSEN LOUIS M. HERMAN ADAM A. PACK SCOTT P. ROBERTS |
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Affiliation: | 1. Kewalo Basin Marine Mammal Laboratory , 1129 Ala Moana Boulevard, Honolulu , HI , 96814 , USA;2. Psychology Department , University of Hawaii , HI , USA;3. Kewalo Basin Marine Mammal Laboratory , 1129 Ala Moana Boulevard, Honolulu , HI , 96814 , USA;4. Psychology Department , University of Hawaii , HI , USA;5. The Dolphin Institute , 420 Ward Ave., Suite 212, Honolulu , HI , USA |
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Abstract: | ABSTRACT A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between two arrays of vertical, air-filled, PVC rods. The blindfolded dolphin was required to station in a submerged, vertically-oriented hoop, 2 radial metres from the stimuli, and indicate whether an array with four rods (S+) was to the left or the right of an array with two rods (S-), by pressing a corresponding paddle. The angular separation between the rods within each array (θw) was maintained at 2 degrees but the angular separation between the two arrays (θb) was varied to produce angular differences (δθ = θb-θw)ranging from 0.25 degrees to 4 degrees. A modified method of constant stimuli was used to test for angular discrimination ability, and yielded a psychometric function having a 75% correct threshold of 1.6 degrees. This threshold fell between the passive listening minimum audible angle thresholds of 0.9 degrees for click signals and 2.1 degrees for a pure tone signal (Renaud & Popper 1975). Analyses of response times, number of clicks and inter-click intervals failed to detect any significant adaptive behaviour occurring as the task became more difficult. These results help to define angular resolution capabilities of dolphin sonar that may play an important role in representing spatial information in the dolphin's environment. |
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Keywords: | dolphin echolocation localisation spatial resolution |
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