Integration of Visual and Echoic Information

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Bottlenosed dolphins have a highly efficient echolocation sense, enabling them to examine their physical world through sound. By emitting short-duration pulsed sounds and listening to the echoes received, dolphins are able to detect and identify objects. Because people lack this sense, it is difficult for us to appreciate the types of mental images or representations of objects that may be formed through echolocation. Dolphins also possess an efficient visual sense that is useful both underwater and in air. Are the images or representations formed through echolocation similar to those formed through vision? Can a dolphin recognize through echolocation an object it has inspected previously only through vision? Conversely, can it recognize through vision an object it has inspected previously only through echolocation? These and related questions are addressed in a set of experimental studies with dolphins at the Kawalo Basin Marine Mammal Laboratory of the University of Hawaii. By examining the types or attributes of objects that may be recognized across the two senses, the researchers will begin to develop ideas about what a dolphin "sees" with its echolocation sense. More fundamentally, the research will also provide information on the theoretical question of the degree to which information from different senses is integrated centrally--what may be called the issue of the unity versus the independence of the senses. Some degree of unity is seen in studies with humans and nonhuman primates of the relationships between vision and active touch. Does a similar degree of sensory unity occur in the dolphin, a nonprimate mammal with many demonstrated intellectual capabilities paralleling those found for nonhuman primates? What might such ability in a dolphin add to ideas about the convergent evolution of intelligence in cetacean and primate brains, which have traced different paths for some 20 million years? On an applied level, might the description of echoic "visualization" by a dolphin offer fresh insights into the construction of intelligent sonar apparatus?