Phantom echo generation: a new technique for investigating dolphin echolocation.

In behavioral experiments where real targets are used to investigate dolphin echolocation, it is often very difficult to extract the relevant echo parameters that the animals use to discriminate or classify. The complex relationship between the physical dimensions and the reflection characteristic of real targets prevents separate control of various echo parameters of the stimuli presented in an echolocation experiment. A new echo simulation method presented in this paper avoids this problem. Dolphin echolocation sounds are transformed with the target impulse response into artificial echoes, which are played back to the animal. The phantom echo system is implemented on a digital signal processing board and gives an experimenter fully programmable control over the echo generating process and the echo structure itself. Echoes of several underwater targets were simulated to evaluate the quality of the method. A comparison of simulated echoes with the original echoes demonstrated very good agreement independent of the incident signal (cross-correlation coefficient > 0.95). The method has tremendous potential for investigating animal echolocation and understanding biosonar signal processing.