ACOUSTIC BASIS FOR RECOGNITION OF ASPECT-DEPENDENT 3-DIMENSIONAL TARGETS BY AN ECHOLOCATING BOTTLE-NOSED-DOLPHIN

The relationships between acoustic features of target echoes and the c ognitive representations of the target formed by an echolocating dolph in will influence the ease with which the dolphin can recognize a targ et. A blindfolded Atlantic bottlenose dolphin (Tursiops truncatus) lea rned to match aspect-dependent three-dimensional targets (such as a cu be) at haphazard orientations, although with some difficulty. This tas k may have been difficult because aspect-dependent targets produce dif ferent echoes at different orientations, which required the dolphin to have some capability for object constancy across changes in echo char acteristics. Significant target-related differences in echo amplitude, rms bandwidth, and distributions of interhighlight intervals were obs erved among echoes collected when the dolphin was performing the task. Targets could be classified using a combination of energy flux densit y and rms bandwidth by a linear discriminant analysis and a nearest ce ntroid classifier. Neither statistical model could classify targets wi thout amplitude information, but the highest accuracy required spectra l information as well. This suggests that the dolphin recognized the t argets using a multidimensional representation containing amplitude an d spectral information and that dolphins can form stable representatio ns of targets regardless of orientation based on varying sensory prope rties. (C) 1996 Acoustical Society of America.