Fig. 6.

Experiment 2. Mean performance of lever-press and chain-pull actions per minute, averaged over 3 min periods, during each of the 4 d of contingency assessment (left four panels) and during the extinction test (right panel). Test performance is divided into two panels: A, showing the data from group sham; andB, showing the data from group GC. In this figure, performance of each action is presented separately in eachpanel according to whether the action-outcome contingency has been degraded, i.e., the outcome delivered by performing the action is the same as the one now delivered without performing the action (Same, filled circles) or has not been degraded, i.e., the outcome delivered by performing the action differs from that delivered without performing the action (Diff, open circles). In thepanel illustrating the extinction test, the previously degraded action-outcome contingency remains designated asSame and the nondegraded as Diff, although no outcomes of any kind were presented in this test.