Tengiz Zorikov

A process of echo-image formation in bottlenose dolphin’s 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 feature’s 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 in order to preserve the image of the reference stimulus in the animal’s perception, it is necessary and sufficient to preserve the same values of the distinctive feature and all higher ones in order of hierarchy. These data were formalized mathematically and used in our computational model, comparative testing of which has revealed critical capabilities comparable with those of bottlenose dolphins. 

Echolocating bottlenose dolphins can detect, discriminate and recognize, with remarkable accuracy, small-size submerged objects slightly differing from each other. Animals, interrogating their environment, utilize echolocation pulses, which, having been examined chaotically, are rather different in structure and duration. However, on-axis emitted clicks, which provide maximally informative echoes, are almost standard once the animal has had experience with the echolocation task. These clicks are usually one and a half period pulses approximately 8–12 ms in duration, with peak frequency of about 80–120 kHz [1–2]. Dolphins identify targets by acute processing of back-scattering echoes of complex multi-highlight structure that contain information about physical characteristics of targets. The sonar system of dolphins is promising for modeling technical analogues, and is the main reason of scientific researches, have studied these animals for more than 40 years in a number of technically advanced countries. The main objective of our studies of the sonar system of dolphins was accumulation of data necessary for the creation of bio-mimetic devices with matching performance. (The aspects of echo discrimination and recognition, but not of echo detection). Accordingly, our attention was focused on echo-processing procedures taking place in the animal’s brain. A set of logically interrelated tests (15 in total) were developed and conducted on the bottlenose dolphins for that purpose, and a computational model was developed based on the gained results [3–7]. Creating the model, we utilized a simple mathematical interpretation of these results, just to check out comparative effectiveness of the feature extracting method revealed in our experiments, in echo-discrimination tasks. We used echo-like signals simulated in a computer and echoes reflected from actual targets to compare effectiveness of the model and dolphin performances. Temporal characteristics of simulated echoes were randomized and white noise was added to complicate discrimination tasks and make them closer to the actual conditions. The real echoes, used in these measurements, were recorded during a matching-to-sample task performed by dolphin

The main objective of our studies of the sonar system of dolphins was accumulation of data necessary to creation of bio-mimetic devices with matching performance. A set of special tests was developed and conducted on the bottlenose dolphins for that purpose, and computational model was embodied on the gained data. This study used synthetic two-highlight echoes with randomized parameters mixed with white noise to compare effectiveness of the model and dolphin performances. The measurements reveal advantage of the model over the bottlenose dolphin’s sonar on signals used. The further steps to the probable improvement of the model are discussed.eps to the probable improvement of the model are discussed.

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.

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