Pigeons' midsession reversal: Greater magnitude of reinforcement on the first half of the session leads to improved accuracy.

In the midsession reversal task, pigeons are trained on a simultaneous two-alternative discrimination in which S1 is correct for the first half of the session and S2 is correct for the second half of the session. Optimally, pigeons should choose S1 until it stops being correct and choose S2 afterward. Instead, pigeons anticipate S2 too early and continue choosing S1 even after the reversal. Research suggests that they attempt to time the reversal rather than use the feedback from the preceding response(s). Recently, there is evidence that performance is almost optimized by generating an asymmetry between S1 and S2. For example, pigeons' accuracy improves if correct S1 responses are reinforced 100% of the time, but correct S2 responses are reinforced only 20% of the time. Similarly, accuracy improves if S1 requires one peck but S2 requires 10 pecks. Accuracy does not improve, however, if the value of S1 is less than the value of S2. In the current experiment, we manipulated the magnitude of reinforcement. For the experimental group, correct responses to S1 were reinforced with five pellets of food and correct responses to S2 were reinforced with one pellet. For the control group, all correct responses were reinforced with three pellets. Consistent with the earlier findings, results indicated that there was a significant reduction in anticipatory errors in the experimental group compared with the control, and there was no significant increase in perseverative errors.