A computational model of the bottlenose dolphin sonar: Feature-extracting method
A process of echo‐image formation in bottlenose dolphin perception was investigated in our experiments, in which animals were trained to differentiate passive actual echoes recorded beforehand purposely, as well as echo‐like simulated impulses. The results suggest that dolphin, processing echoes within critical interval of time (∼0.2 ms), utilizes the string of three independent, hierarchically organized features (echoes subjective characteristics) being defined by different scales of spectral density oscillation, and energy. Herewith, dolphin is capable to assess features average value over a series of echoes. Distinguishing stimuli, dolphin estimates successively features values from senior to minor, terminating the process at the feature, which contains detectable differences in compared stimuli (the distinctive feature). A procedure of subsequent identification of the reference stimulus can be described by the following decision rule: If the dolphin utilizes some feature as the distinctive one, then i...
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.
Signal processing of the echo signatures returned by submerged shells insonified by dolphin "clicks:" active classification.
A large set of dolphin-emitted acoustic pulses ("echolocation clicks") have been examined, which were reflected from various elastic shells that were suspended, underwater, 4.5 m in front of the animal in a large test site in Kaneohe Bay, Hawaii. A carefully instrumented analog-to-digital system continuously captured the emitted clicks and also the returned, backscattered echoes (A/D conversion at 500 kHz). Using standard conditioning techniques and food reinforces, the dolphin is taught to push an underwater paddle when the "correct" target-the one he has been trained to identify-is presented to him. He communicates his consistently correct identifying choices in this manner. Many echoes returned by three types of cylindrical shells in both the time and frequency domains as well as in the joint time-frequency (t-f) domain, by means of Wigner-type distributions have been examined. It will be shown exactly how specific features observable in these displays are directly related to the physical characteristics of the shells. This processing takes advantage of certain fundamental resonance principles to show which echo features contain information about the size, shape, wall thickness, and material composition of both the shell and its filler substance. In the same fashion that these resonance features give the identifying characteristics of each shell, it is believed they may also give them to the dolphin. These echo features may allow him to extract the target properties by inspection without any need for computations. It is claimed that this may be the fundamental physical explanation of the dolphin's amazing target ID feats, upon which they base their recognition choices. This claim may be substantiated by the detailed analysis of many typical echoes returned by various shells, when they are interrogated by several dolphins. Thus far, this analysis of many echoes from many shells has only been carried out for a single dolphin.