[Model of the bicercal mechanism of constant direction perception of a mechano-acoustic signal in the insect].

Model of signal processing in mechano-acoustical cercal system of insects is described in which the invariance of the perceived signal direction with respect to the positions of sense organs (cerci) is achieved due to connections of four central neurons with certain receptor groups on both cerci. The data published earlier suggest that the monocercal constancy mechanism for invariant estimation of signal direction is based on a proper change in the weights of receptoral inputs to the central neurons in accordance with the position of each cercus. In contrast with it the bicercal constancy mechanism discussed in this paper does not imply either any regulation of receptoral inputs to the central neurons or some other utilization of information about the position of sense organs at the moment of signal perception. The model is based on two properties of the cercal system: on each cercus there are receptors with optimal directions of stimulation which are parallel and perpendicular to the cercus axis; two cerci usually occupy symmetrical positions relative to the insect body. Signal processing in the proposed neural circuit is equivalent to the signal direction estimation by projecting the vector of velocity on the two stable basic directions whose orientations do not change when symmetrical changes in cercus positions occur.