Horizontal angular discrimination by an echolocating bottlenose dolphin ( Tursiops   truncatus )

• Published in: The Journal of the Acoustical Society of America Vol. 108; no. 5_Supplement; p. 2636
• Main Authors: Branstetter, Brian K., Herman, Louis M., Pack, Adam A., Mevissen, Sonja J., Moore, Amanda M., Granum, Jamie, Carsrud, Lea, Butler, Carol, Lecaroz, Sarah B., Roberts, Scotty
• Format: Journal Article
• Language: English
• Published: 01-11-2000
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4743813

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 meters from the stimuli and indicate if 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 rods within each array were separated by 2 deg and the two arrays were separated by eight different angles between 2.25 and 6 degrees. A modified method of constant stimuli was used to test for angular discrimination ability. The results yielded a high-pass psychometric function with an arbitrary 75% correct threshold of 1.5 deg. These data agree well with passive listening minimum audible angle thresholds of 0.9 deg for click signals and 2.1 deg for a pure tone signal (Renaud and Popper, 1975). Analyses of response times, number of clicks and inter-click intervals suggested no significant adaptive behavior was used as the task became more difficult. These results help define angular resolution capabilities of dolphin sonar that may play an important role in representing spatial information in the dolphin’s environment.