2.2. ResultsThe points in the top p

2.2. Results
The points in the top panel of Fig. 1 represent, for each session, the mean proportion of trials with a head entry. The solid symbols represent responding to Stimulus A; the open symbols, to Stimulus B. Rats initially responded to A and B on 85% of the trials (Condition 1, Acquisition). As training progressed in this condition, responses to B (the CS−) dropped to 40%, whereas responses to A (the CS+) remained above their initial frequency. Under Extinction (Condition 2), responding to A and B declined to 15 and 5% of trials, respectively. On the first session in which the CS+ was reinstated (Condition 3, Reacquisition), responding to A and B recovered to pre-extinction levels. Responding to A during Reacquisition remained relatively stable, whereas responding to B declined to 30% of trials, seemingly continuing the downward trend observed during Acquisition and interrupted by Extinction. Extinction performance was replicated in the second Extinction condition (Condition 4). When the dipper activations were reinstated, but following B and not A (Condition 5, Reversal), responding to A and B recovered close to pre-extinction levels, but whereas responding for B (now the CS+) rose over 90% of trials within 4 sessions and remained at that level, responding for A (now the CS−) slowly dropped to 70% of trials. Prior extinction performance was essentially replicated in the third Extinction condition (Condition 6). Reversal performance in Condition 5 was replicated in the second Reversal condition (Condition 7), but with A as CS+ and B as CS−. Prior extinction performance was again replicated in the final Extinction condition (Condition 8). Responding to A (CS+) during the final Reacquisition (Condition 9) remained relatively stable, whereas responding to B (CS−) declined to 35% of trials. The latter was a replication of the first Reacquisition (Condition 3), and like then, responding to A and B during the second Reacquisition appeared to continue the trend observed before Extinction.