Recent publication: Branstetter, B. K., Mevissen, S, J., Herman, L, M., Pack, A. A., Roberts, S. P. (2003). Horizontal angular discrimination by an echolocating bottlenose dolphin (Tursiops truncatus). Bioacoustics 14, 15-34.
A bottlenose dolphin was tested on its ability to echoically discriminate horizontal angular differences between two arrays of vertically oriented 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 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 (qw) was maintained at 2 degrees but the angular separation between the two arrays (qb) was varied to produce angular differences (Dq= qb-qw) 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). Analysis of response times, number of clicks and inter-click intervals failed to detect any significant adaptive behavior 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. Please contact [EMAIL PROTECTED] for reprint requests.
