Phantom echo highlight amplitude and temporal difference resolutions of an echolocating dolphin, Tursiops truncatus

A dolphin's ability to discriminate targets may depend greatly on the relative amplitudes and the time separations of echo highlights within the received signal. Previous experiments with dolphins varied the physical parameters of targets, but did not fully investigate how changes in these parameters correspond with the scattered acoustic wave forms and the dolphin's subsequent response. This experiment utilizes a phantom echo system to test a dolphin's detection response to relative amplitude differences of secondary and trailing echo highlights and the time separation differences of all the echo highlights both within and outside the animal's integration window. By electronically manipulating the amplitude and temporal separation of the echo highlights, the underlying acoustic classification cues are more efficiently investigated. The animal successfully discriminated between a standard echo signal and one with the secondary highlight amplitude lowered by 7 dB from the standard. Furthermore, the animal successfully discriminated between a standard echo signal and one with the trailing highlight amplitude lowered by 3 dB from the standard and also a standard echo signal and one with a time separation of 150 mus between the secondary and trailing highlights.