Table 1 shows these conditions with number of sessions in the order they occurred. Acquisition (Condition 1) occurred as described above. During all Extinction conditions (Conditions 2, 4, 6, and 8), dipper presentations were discontinued following presentation of both conditional stimuli. Following Extinction conditions, the original contingencies prior to Extinction were reestablished during Reacquisition conditions (Conditions 3 and 9) or were reversed between conditional stimuli during Reversal conditions (Conditions 5 and 7). To keep track of the stimulus assignments throughout all conditions, the CS+ and CS− stimuli arranged during the initial Acquisition condition will be referred to as Stimulus A and Stimulus B, respectively, throughout (regardless of whether they are the CS+ or CS−).