[The study of individual differences as a method for dividing into stages the acquisition of a complex reflex].

Two-way active avoidance learning is a complex task characterized by a high level of interindividual variability. We have demonstrated in our previous paper that rats with different rate of learning vary in expression of freezing responses, which reflects a conflict tendency not to re-enter the previous chock compartment [4]. In the present work we analyzed as main indices the proportions of avoidance, rapid escape, and freezing responses and their distribution within a session. Sequences of occurrence of these three types of responses were examined in groups of rats with different success of avoidance learning. The obtained results confirmed a hypothesis that overcoming the conflict tendency was a separate stage of learning which preceded avoidance response appearance and subsequent stabilization. Only in rats which failed to learn and develop avoidance responses within the first session, freezing responses were observed in successive session being indicative of reappearance of the conflict tendency. The intensity of the conflict tendency did not depend on the type of the first response of an animal (fleeing or freezing) to an unexpected aversive stimulus.