| Abstrakt: |
This study analyzes the algorithm by which a distributed system of neurons evaluates specific features in sensory feedback and thereby controls a behavioral response. The electric fish Eigenmannia raises or lowers the frequency, f, of its electric organ pacemaker in response to a neighbor's frequency, f, which is slightly lower or higher respectively than its own frequency. This Jamming Avoidance Response (JAR) thus serves to increase the difference in frequencies, Δf=f− f, which is necessary to enhance the animal's electrolocation ability. The JAR is driven by electroreceptive afferences from the individual's electric organ discharges (EODs) which, in different parts of the body surface, are unevenly contaminated by EODs of the other fish. This can be demonstrated, in an open loop experiment, by replacing the silenced, nearly sinusoidal EODs of a curarized fish by a sine wave stimulus, S, mixed with a similar stimulus, S, which mimicks EODs of another fish. The JAR is controlled by joint modulations of instantaneous phase, H, and amplitude, ¦ S¦, of the composite signal, S+S. These modulations, if plotted in a two-dimensional state-plane with H and ¦ S¦ as its axes, form a circular graph whose sense of rotation is counterclockwise for positive Δfs and clockwise for negative Δfs. The sense of rotation thus determines the direction in which the pacemaker frequency is to be shifted. Modulations of H and ¦ S¦ are encoded by specialized electroreceptors, T- and P-units respectively (Fig. 1). Applying various forms of artificial computer generated modulations of phase and amplitude, many of which never occur in a natural situation, and by independently stimulating different parts of the curarized animal's body surface, we demonstrate the following: The findings in this paper are based on behavioral experiments on basically intact animals. The subsequent paper treats neuronal correlates of the JAR. [ABSTRACT FROM AUTHOR] |
