Object Perception and Representation by Echolocating Dolphins

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Object Perception and Representation by Echolocating DolphinsPrincipal Investigator: Louis M. Herman Ph.D.This research continues the investigation by this laboratory of the ability of the bottlenosed dolphin (Tursiops truncatus) to perceive the shape of objects through its echolocation sense. How does the dolphin represent objects it inspects through echolocation? Does it perceive only the raw echoes returning from ensonified objects or, like vision, does it directly perceive the shape of the object? The prior-published studies used a cross-modal matching-to-sample procedure to demonstrate that a dolphin could spontaneously recognize objects across the senses of echolocation and vision. The results suggested that object shape is directly perceived though the echolocation sense, and that the representations of objects obtained through echolocation are coordinated with or closely integrated with the representations obtained through vision. These conclusions strongly revise previous views of dolphin echolocation that postulated that discriminations among different objects were based on learning to associate the raw acoustic cues of returning echoes (e.g., amplitude, highlight structure, or spectral composition) with things seen or with reward received. The continuing investigations now ask how faithfully the dolphin's representations preserve the spatial structure of the object being ensonified, and what mechanisms can support the construction of a shape percept through echolocation. Other questions include whether the dolphin's perception of shape though echolocation is invariant with changes in the orientation of the object, with changes in material composition of the object, and with changes in object size. In each manipulation, object shape will remain constant, but the sound reflection properties of the object will vary. The cross-modal matching technique will continue to be used, as well as intra-modal techniques in which object recognition performance is examined within the senses of echolocation and vision rather than across the senses. The issues considered in these studies and the findings obtained establish links with issues and findings in object-based perception and in intersensory perception in infant and adult humans, and in nonhumans. The studies also make contact with general issues in memory and representation in human and nonhuman animals.