Echo highlight amplitude and temporal difference resolutions of an echolocating Tursiops   truncatus

A dolphin’s ability to discriminate targets may greatly depend on the relative amplitudes and the time separations of echo highlights within the received signal. Previous experiments with dolphins have varied the physical parameters of targets, but did not fully investigate how changes in these parameters corresponded with the composition of the scattered acoustic waveforms and the dolphin’s subsequent response. A novel experiment utilizes a phantom echo system to test a dolphin’s detection response of relative amplitude differences of secondary echo highlights and the time separation differences of all the echo highlights both within and outside the animal’s integration window. By electronically manipulating these echoes, the underlying acoustic classification cues can be more efficiently investigated. In the first study, the animal successfully discriminated between a standard echo signal and one with the middle highlight amplitude at −7 dB. When the middle highlight amplitude was raised to −6 dB, the animal’s discrimination performance radically dropped to 65%. This study suggests the animal may not be as sensitive to the secondary echo highlights as previously proposed. The experiments were repeated for the trailing highlight amplitude and the time separations between the primary and middle highlights and the middle and trailing highlights.