The following article on Kewalo Basin Marine Mammal Laboratory's ongoing
investigations of dolphin echolocation perception through cross-modal
recognition has recently been published in the journal Behavioural
Processes. Reprints will be available shortly. Please send reprint
requests to Adam Pack at email@example.com.
Pack, A. A., Herman, L. M., Hoffmann-Kuhnt, M., & Branstetter, B. K. (2002).
The object behind the echo: dolphins (Tursiops truncatus) perceive object
shape globally through echolocation. Behavioural Processes, 58, 1-26.
Two experiments tested a bottlenosed dolphin¹s ability to match objects
across echolocation and vision. Matching was tested from echolocation
sample to visual alternatives (E-V) and from visual sample to echolocation
alternatives (V-E). In Experiment 1, the dolphin chose a match from among
three alternative objects that differed in overall (global) shape, but
shared several 'local' features with the sample. The dolphin conducted a
right-to-left serial nonexhaustive search among the alternatives, stopping
when a match was encountered. It matched correctly on 93% of V-E trials and
on 99% of E-V trials with completely novel combinations of objects despite
the presence of many overlapping features. In Experiment 2, a fourth
alternative was added in the form of a paddle that the dolphin could press
if it decided that none of the three alternatives matched the sample. When
a match was present, the dolphin selected it on 94% of V-E trials and 95% of
E-V trials. When a match was absent, the dolphin pressed the paddle on 74%
and 76%, respectively, of V-E and E-V trials. The approximate 25% error
rate, which consisted of a choice of one of the three non-matching
alternatives in lieu of the paddle press, increased from right to center to
left alternative object, reflecting successively later times in the
dolphin¹s search path. A weakening in memory for the sample seemed the most
likely cause of this error pattern. Overall, the results gave strong
support to the hypothesis that the echolocating dolphin represents an object
by its global appearance rather than by local features.
Adam A. Pack, Ph.D., Assistant Director
Kewalo Basin Marine Mammal Laboratory
1129 Ala Moana Blvd.
Honolulu, HI 96814
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