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LABORATORY FOR THE SENSORY SYSTEMS OF VERTEBRATES
MAIN GOALS AND TASKS
Professor, Laureate of the State Prize of the USSR A.Ya. Supin
Electrophysiological Laboratory at the Utrish Marine Station
Ecology of organisms and communities.
The most important achievements of the laboratory for the latest 10 years:
In the field of cetaceans hearing research:
The technique of electrophysiological study of cetaceans hearing was developed, with the application of which the data about hearing selectivity in cetaceans to the main characteristics of the sound signals (frequency, temporal structure, spatial location of the sound source) were obtained. Acuteness of the frequency selectivity (quality of the filters canals in the auditory system) in different species of dolphins constitutes the range of 30 to 50 that is 3-5 times higher than in most terrestrial mammals (excluding bats) and humans (about 10). Temporal resolution of the auditory system in dolphins allows to discriminate of fluctuations with the frequency up to 1500 per sec (in humans – unup to 50-70 per second).
Selectivity to the spatial location of the sound source results from a very steep dependence of inter-aural intensity difference on azimuth in the frontal sector: 1-2 dB/degree. At the threshold of inter-aural intensity difference of 0.5-1 dB this provides the accuracy of the sound source localization better than 1 degree. To investigate mechanisms of such a high selectivity, an original method was developed that determined position of "acoustic windows" - the parts on the body surface through which transmission of sound energy to the auditory organ occurred (the method was based on measurement of acoustic delays which allowed to determine the distances from the sound source to the "acoustic window"). The measurements carried out by this method revealed at least two acoustic windows with different directions of the best-sensitivity axis and with different frequency responses. Combination of signals from these two windows provides high spatial resolution of hearing.
In the field of cetacean echolocation research:
The method of registration of electric responses of the dolphin brain in the process of echolocation was developed. Recordings contained components, which were responses to both the emitted echolocation pulse and to the echo. Thereby a new instrument to study the mechanisms of analysis of echolocation information in the auditory system was elaborated. With the use of this method, a highly effective mechanism of automatic gain control (AGC) in the auditory system of dolphins was determined, making the responses of the auditory system little dependent on the distance to the located target. The mechanism of AGC implies interaction between the emitted and echo signals in the auditory system, and this interaction compensates for the dependence of the echo level on distance.
In the field of vision research in aquatic mammals:
Using morphologic investigation of ganglion layer of the retina, topographic organization of the visual fields in several cetaceans and pinnipeds was studied. The presence of the zones of high concentration of ganglion cells in the retina, i.e. the zones of high resolution in the visual field was shown. There are two zones of the best vision in cetaceans: in the nasal and temporal sectors of the visual field that provides universal aquatic-aerial vision and a wide coverage sector. In pinnipeds, there is one zone of the best vision similar to terrestrial Carnivora. On the basis of the data obtained, visual acuity of a number of cetaceans and pinnipeds was calculated. An new mechanism of increase of retinal resolution due to cluster grouping of ganglion cells was revealed.
In the field of psychophysical research of human's hearing:
The ability of human's hearing to discriminate complex spectral patterns of sounds was investigated, particularly in background of interfering noises. It was shown that interfering noise evoked deterioration of spectral discrimination, but at that the mechanisms of noise influence differed for noise coinciding or not coinciding with the spectrum of the probe signal. The difference in the spectra of noise and probe didn't eliminate the deteriorating influence of the noise, but an effective, practically complete binaural release of the noise influence took place.
The dolphin - false killer whale with a sensor-sucker
Hearing sensitivity of dolphins is one-order higher than the hearing sensitivity of man, the acuity of frequency tuning in dolphins exceeds that in man in several times, temporal resolving capacity – in dozens of times.
In the field of kinematics and hydrodynamics research in dolphins:
It was shown that critical influence on the character of water flow along the dolphin body in the process of its active swimming was exerted by forming on its body of the favorable gradient of dynamic pressure, which promoted significant laminarization of the interface and increase in the critical value of the Reynolds number. This led to economy of the energy (2-3 times) in the process of swimming and confirmed the existence of "Grey paradox". A mathematical model of this event was created. The fallaciousness of previous views was demonstrated according to which the dolphin was able to develop very great powers and needn't any mechanisms of resistance lowering. The correct estimation showed that the meanings of the pulling power of the dolphin were quite moderate, and calculated coefficients of resistance took place predominantly between turbulent and laminar values. Thus, the problem of dolphin hydrodynamics formulated in 1936 by J. Grey got a new light and a stimulus to further development.
A comparatively simple theory of hard hydrodynamic wing, modeling the caudal blade of the dolphin was developed. The formulas for calculation of hydrodynamic forces, developing by the wing for its different forms, kinematic modes of action and arbitrary values of amplitudes, angles of fluctuations and positions of pivot pin were created. The comparison of the calculated values of the traction, developed by the hard wing, with experimentally measured values showed their good concordance.