Animal behavior in the irrelevant situation has been paid little attention in contrast to that in the relevant situation, i. e., typical conditioning researches. The present article reviewed the researches using the “dual-training paradigm” for investigating the animal behavior in the irrelevant situation which includes “learned irrelevance” and “learned helplessness” phenomena. To classify the researches, three criteria were applied; type of training (S-S* or R-S*), type of S* (aversive or appetitive), and type of contingency (+, -, or 0). The classification made it clear the direction of investigation.
