Analysis of auditory information in the brains of cetaceans.

A characteristic feature of the brains of toothed cetaceans is the exclusive development of the auditory neural centers. The location of the projection sensory zones, including the auditory zones, in the cetacean cortex is significantly different from that in other mammals. The characteristics of evoked potentials demonstrate the existence of several functional subdivisions in the auditory cortex. Physiological studies of the auditory neural centers of cetaceans have been performed predominantly using the evoked potentials method. Of the several types of evoked potentials available for non-invasive recording, the most detailed studies have been performed using short-latency auditory evoked potentials (SLAEP). SLAEP in cetaceans are characterized by exclusively high time resolution, with integration times of about 0.3 msec, which on the frequency scale corresponds to a cut-off frequency of 1700 Hz. This is more than an order of magnitude greater than the time resolution of hearing in terrestrial mammals. The frequency selectivity of hearing in cetaceans has been measured using several versions of the masking method. The acuity of frequency selectivity in cetaceans is several times greater than that in most terrestrial mammals (except bats). The acute frequency selectivity allows the discrimination of very fine spectral patterns of sound signals.