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.
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