Bioacoustics and physiology of hearing
 

Studying the human and animal auditory systems with electrophysiological and morphological methods and modelling them as signal processing systems, studying low frequency sound influence on marine animals, methods of bioacoustical monitoring of the ocean.

The bioacousical group in Acoustics Institute was organized under the initiative of academician N. N. Andreyev at the end of the 50th. During a long time the acting institute director N. A. Dubrovsky had been the head of the group. At present time the head of the group is N. G. Bibikov.

The main scientific interest of the group is connected with the study of the sound processing in the neural auditory pathway.

During more than four decades the stuff of the group has been exploring the information processing in peripheral and central auditory regions of the frog. The frogs seem to be a simple and convenient object for studying of auditory processing. These animals demonstrate both good hearing and active auditory communication, having comparatively simple structure of the auditory pathway. We believe that auditory processing in frogs has many common features with auditory processing in mammals. The study was performed mainly by single cell's recording using home-made software for signal generation and software for data processing.

The direct estimations of the main parameters of neurons (time constant of integration, level of internal noise, etc.) were received for many cells located on different levels of the system. Many specialized cells, allocating separate attributes of sound signals (frequency peaks of the carrier and envelope, modulation depth, duration, on/off ratio, etc.) were found out.

Neural activity on various levels of the auditory system during the action of amplitude-modulated signals was investigated in the most detail. Two effects were founded out. The first is the considerable enhancement of the neural response to small amplitude changes during the long-term adaptation. This effect manifests itself dramatically in the situation when an amplitude-modulated segment is embedded in a long pure tone.

The initial part of this effect was explored. The considerable increase of the synchronization to the stimulus waveform during the initial part of amplitude-modulated tone bursts was demonstrated. The response to a single "auditory events" (increment or decrement in amplitude) increased with the delay of this event from onset of a tone burst. The last observation can be treated as a physiological analog of psychophysical "overshoot effect".

The second effect is the high resistance of the periodicity extraction to noise inference of the modulation waveform. Moreover, in adapted state the low-frequency noise could improve the extraction of small envelope periodicity. We considered these data as a demonstration of "a stochastical resonance" phenomena in auditory system. Even more pronounced enhancement of hidden periodicity could be observed when very low sinusoid was added to small higher frequency modulating waveform.

The modelling of these effects is now under study.