Seeing through Sound
Echolocation is the process of detecting and identifying objects
by emitting sounds, such as the broadband clicks used by dolphins,
and listening to the
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| Dolphin inspects object inside box using
echolocation. |
echoes returning from objects reflecting those sounds. A recent discovery
we made is that dolphins appear capable of directly perceiving the
shapes of objects through echolocation. Prior to this finding, it
had been generally assumed that dolphins learned to identify and recognize
objects through echolocation by a process of associative learning-by
comparing the echoes returning from targets with the visual appearance
of those targets.
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| Dolphin chooses the object visually from
3 alternatives. |
Instead, our work has shown that echolocation can yield an immediate
perception of the shapes of objects without any intervention by
associative learning. We established this finding by asking the
dolphin to inspect an object inside of a visually opaque box, using
echolocation alone, and then to find a match for that object from
among two or more objects inspected through vision alone. The box
was filled with water and an object was suspended inside in the
water column. The front of the box, constructed of a thin sheet
of black Plexiglas, allowed sound to penetrate but preventing any
visual view inside the box. The objects shown to the dolphin's visual
sense were held in air, a medium in which echolocation is ineffective.
We also studied the reverse condition, in which the dolphin was
required to
examine an object visually, and then select a match from two or
more boxes, each containing an object. In either case, echolocation
to vision or vision to echolocation, the dolphin's matching performance
for objects of a variety of shapes was almost perfect. These findings
suggested strongly that the mental representations of objects developed
through echolocation are integrated with or closely coordinated
with those developed through vision. In effect, then, the dolphin
can "see" though sound.
Click here to see
a virtual reality VRML of the experimental setup of this study.
Pack, A. A., Herman, L. M., & Hoffmann-Kuhnt
(in press). Dolphin echolocation shape perception: From sound to
object. In J. Thomas, C. Moss, & M. Vater (Eds.). Echolocation
in Bats and Dolphins. Chicago: University of Chicago Press.
Pack, A. A. & Herman
L. M. (1995). Sensory integration in the bottlenosed dolphin: Immediate
recognition of complex shapes across the senses of echolocation
and vision. Journal of the Acoustical Society of America, 98, 722-733.
Herman, L. M., Pack,
A. A., & Hoffmann-Kuhnt, M. (1998). Seeing through sound: Dolphins
perceive the spatial structure of objects through echolocation.
Journal of Comparative Psychology, 112, 292-305.
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