Discrimination of mixed-directional whistles by a bottlenose dolphin (Tursiops truncatus)

Abstract

Dolphins are hypothesized to deduce the swimming direction of group members by attending to the spectral pattern of whistle harmonics. This is known as the direction of movement cue hypothesis and may facilitate coordination of complex group behavior when visibility is poor. The direction of movement cue hypothesis hinges on the assumption that dolphins can discriminate between whistles with different harmonic patterns that are associated with signaler orientation. This assumption was tested with a bottlenose dolphin. Whistles were recorded from a dolphin at different azimuth positions (0° to 180° in 45° increments). Noise-free, synthetic whistles were created to mimic the direction-dependant spectral profiles of the recorded whistles. A dolphin was then tested in its ability to discriminate between the synthetic whistles using fixed level and roving level conditions. The dolphin's discrimination performance in both the fixed and roving level conditions was near 100% for whistles separated by angles greater than 45°, and near chance for 45° separations. Computer simulations of the task, along with the dolphin's performance, suggest that the dolphin's discrimination was level invariant and based on the spectral pattern of the whistles.

Forward shift of feeding buzz components of dolphins and belugas during associative learning reveals a likely connection to reward expectation, pleasure and brain dopamine activation

“…The VS had nothing to do with the goal of the experiments (Ridgway et al, 1969;Ridgway et al, 1984;Ridgway et al, 1991a;Ridgway et al, 1991b;Schlundt et al, 2000;Ridgway et al, 2001;Blackwood, 2003;Moore et al, 2008;Ridgway, 2011;Branstetter et al, 2012;Branstetter et al, 2013). We observed no differences in the trials where no VS was recorded after an SR.…”

“…We have heard the VS during different experiments on hearing and sound production (Ridgway and Carder, 1988;Ridgway et al, 1991b;Ridgway and Carder, 1997;Schlundt et al, 2000;Ridgway et al, 2001;Moore et al, 2008;Ridgway, 2011;Branstetter, 2012;Branstetter, 2013). However, in none of these studies did we define the metrics of these incidental vocalizations.…”

“…Both of these particular pulsed sounds remind us of a child's squeal of delight. Thus we named them victory squeals (VS) (Ridgway et al, 1991a;Ridgway and Carder, 1998;Finneran, 2013;Branstetter et al, 2013). Both dolphins and belugas produce many bursts of pulses in many different behavioral contexts.…”

Recognition of Frequency Modulated Whistle-Like Sounds by a Bottlenose Dolphin (Tursiops truncatus) and Humans with Transformations in Amplitude, Duration and Frequency

“…In the current study, the dolphin SAY’s ability to recognize frequency modulated tones was robust to changes in amplitude and duration, but constrained by absolute frequency. Although the dolphin SAY had extensive experience in cognitive tasks [ 27 , 28 ] and psychoacoustic tasks [ 30 ], this study, as well as all studies with a limited subject pool, should be interpreted with caution. Replication of this study (and similar laboratory studies) is difficult due to obstacles associated with housing and long-term training.…”

“…An Atlantic bottlenose dolphin (SAY, female, age 36, Tursiops truncatus ) with extensive experience in cognitive [ 27 , 28 ] and psychophysical testing [ 29 , 30 ] participated in the experiment. She had normal hearing sensitivity at the frequencies tested as determined via auditory evoked potential testing [ 31 ].…”