Hierarchical resurgence.

In resurgence, conventionally a target response is trained and then extinguished while some alternative response is reinforced. In the most common procedure, when the latter is extinguished, the former resurges. The present experiments examined resurgence after two responses were trained sequentially and subsequently extinguished. In Experiments 1 and 2, keypecking to one key was trained and then extinguished as keypecking to a different key was trained then later extinguished. In both experiments, regardless of the spatial location of the different keys, the last-trained response resurged before the first-trained one. The results were replicated in Experiment 3 where reinforcement rate of the first-trained response was four times that of the second-trained response. The results in conjunction with earlier experiments suggest that resurgence occurs hierarchically, although whether more or less recently trained target responses resurge first or later may depend on both current and historical variables. The results also raise questions about the interpretation of responding on a control key that sometimes is included in resurgence experiments to isolate resurgence from extinction-induced responding.