Vocal Mimicry of Computer-Generated Sounds and Vocal Labeling
of Objects by a Bottlenosed Dolphin, Tursiops truncatus
- Douglas G. Richards, James P. Wolz, Louis M. Herman
(C) 1984 by the American Psychological Association, Inc.
A bottlenosed dolphin (Tursiops truncatus) was trained to mimic
computer-generated “model” sounds, using a whistle mode
of vocalization. Prior to training, the whistle sounds of this dolphin
were limited to a few stereotyped forms, none of which resembled
the model sounds. After training, high-fidelity imitations were
obtained of model sounds having (a) moderately or widely swept,
slow-rate frequency modulation (1-2 Hz), (b) narrowly or moderately
swept frequency modulation at m moderate to rapid rates (3-11 Hz),
(c) square-wave frequency transitions. and (d) unmodulated (pure-tone)
waveforms. New models, not heard previously, could be mimicked immediately,
often with good fidelity, including mimicry of amplitude variation
that had not been explicitly reinforced during training. Subsets
of familiar models were mimicked with high reliability in repeated
tests. In additional training, control of the mimic response was
transferred from the acoustic model to objects shown the dolphin
(e.g., a ball or a hoop) so that, in effect, the dolphin gave unique
vocal labels to those objects. In a test of accuracy and reliability
of labeling, correct vocal labels were given on 91% of 167 trials
comprised of five different objects presented in random order. The
dolphin’s ability for vocal mimicry compared favorably with
that of the more versatile mimic birds, and it contrasted sharply
with the apparent lack of vocal mimicry ability in terrestrial mammals
other than humans. The ability to label objects vocally was similar
to abilities shown for some birds and similar, in principle, to
abilities of great apes trained in visual languages to label objects
through gestures or other visual symbols.
Richards, D. G., Wolz, J. P. & Herman, L. M. (1984). Vocal mimicry
of computer generated sounds and vocal labeling of objects by a
bottlenosed dolphin, Tursiops truncatus. Journal of Comparative
Psychology, 98, 10-28.
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