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
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.
| Dolphin inspects object inside box using echolocation. |
| 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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