Echo-processing procedure in bottlenose dolphins

For investigation of the echo-processing mechanisms in dolphins a set of logically interrelated tests is developed. In these experiments animals are trained to differentiate simulated echo-like signals and echoes from actual targets. Application of this set of tests to the Black Sea bottlenose dolphins revealed that signal components highlighted within a time interval /spl sim/0.2 ms are shown to produce a merged auditory image in dolphins´ perception. By analysis of echo within this time window, dolphins utilize three independent discriminative features being determined by the different scale of spectral density oscillations of the echo and by its energy. The animals do not assess differences in signals´ polarity. The invariant hierarchical relations between these features were found out, and the structure of the hierarchy was established. The ability of animals to evaluate an average value of the dominant feature in a series of echoes was demonstrated as well. The decision rule describing the process of echoes identification by the dolphins is stated.