Discrimination of the signals with identical energy spectra by the bottlenose dolphin

Abstract

Dolphins are capable of discriminating a small click followed by a large click from a time reversed pair of the same clicks. Because the time reverse of a signal does not change its energy spectrum it appeared that the dolphins discriminated the waveforms of the mirror image double clicks. A short-time spectral analysis with a 0.3-ms chi-square window has been suggested as an alternative to the time domain discrimination of the double clicks with identical energy spectra. The length of the analysis window was chosen based on the dolphin's auditory time resolution of around 0.3 ms and integration time of 0.265 ms. Dolphin's discrimination of three different types of time mirror image signals is discussed in this paper. Our experiments indicate that the dolphin's auditory analysis window is not bigger than around 0.1 ms. The dolphin's performance appeared to be more coherent with the time domain analysis of the mirror image stimuli than with the short-time frequency analysis.