Institute of Biology of Inland Waters, Russian Academy of Science, Borok, Yaroslavskaya obl. 151742, Russia

Abstract

Animal's responses to repeated identical stimulation are notoriously variable. The variability is not always resulted from differences between individuals, stimulus action, or habituation. Goldfish(s responses to a visual stimulus were studied in order to reveal the nature of variability. The experimental device consisted of a white circular corridor, and the black band stimulus drown across the corridor. Fish responded to the stimulation by an increase in frequency of turns in the vicinity of the band. The response, however, was not always positive: sometimes fish passed by the band with no turns (negative response). The significant tendency to repeat positive and negative responses by series was observed. Intensity of the response differed between individuals, and some individuals never responded at all. The simulating dynamic model of goldfish behaviour was studied both qualitatively and quantitatively. The model assumes that the control mechanism of the behaviour is influenced by the noise (fluctuations of nervous activity) which causes phase transitions in the mechanism. The similarity of the model(s behaviour to experimental data suggests that the response variability observed in goldfish resulted from the self-organising process. Therefore, the variability should persist even in the absence of any variations in an external stimulation, as well as in the absence of individual differences.