Some general principles of signal processing in the auditory system.

Overview of the current state of problems connected with some general principles of sounds coding of in auditory system is presented. It is emphasized that after transformation in the cochlea an auditory signal is presented only as a pulse activity in a population of auditory nerve fibers. Statistical independence of firing in different fibers is urgently required in order to encode spectro-temporal features of the sound in very big frequency and dynamic ranges. Complex mechanism of frequency analysis in cochlea as well a specific system of synaptic transmission between inner hair cells and auditory nerve fibers serve to ensure this independence. The presence of independent noise components in each fibers also serves the same aim. These properties allow to code in a population of fibers such time intervals which are considerably shorter than duration of a single neuron's pulse (spike). On the following levels of the auditory pathway this information is processed by several different methods. As a consequence a sharp increase in the number of single neurons takes place along the auditory pathway. Starting from the auditory midbrain center the plasticity of the nervous tissue is becoming increasingly important. Virtually every nerve cell could be considered as a self-learning element, which internal properties are determined mainly by its prior experience. The experimental data which serves to justify the expressed provisions are discussed.