Pigeons show near-optimal win-stay/lose-shift performance on a simultaneous-discrimination, midsession reversal task with short intertrial intervals

Abstract

Discrimination reversal tasks have been used as a measure of species flexibility in dealing with changes in reinforcement contingency. The simultaneous-discrimination, midsession reversal task is one in which one stimulus (S1) is correct for the first 40 trials of an 80-trial session and the other stimulus (S2) is correct for the remaining trials. After many sessions of training with this task, pigeons show a curious pattern of choices. They begin to respond to S2 well before the reversal point (they make anticipatory errors) and they continue to respond to S1 well after the reversal (they make perseverative errors). That is, they appear to be using the passage of time or number of trials into the session as a cue to reverse. We tested the hypothesis that these errors resulted in part from a memory deficit (the inability to remember over the intertrial interval, ITI, both the choice on the preceding trial and the outcome of that choice) by manipulating the duration of the ITI (1.5, 5, and 10 s). We found support for the hypothesis as pigeons with a short 1.5-s ITI showed close to optimal win-stay/lose-shift accuracy.

Figure 1

Percentage choice of S1 as a function of trial number (in blocks of 5 trials) averaged over Sessions 31–40 for Group 1.5 (filled circles), Group 5 (open circles), and Group 10 (open triangles). Error bars = ±1 sem

Figure 2

Percentage choice of S1 as a function of trial number for Trials 36–40 (immediately prior to the reversal) and Trials 41–45 (immediately after the reversal) averaged over Sessions 31–40 for Group 1.5 (filled circles), Group 5 (open circles), and Group 10 (open triangles). Error bars = ±1 sem.

Figure 3

Mean number of one-error sessions during training for Group 1.5, Group 5, and Group 10. Error bars = ±1 sem.

Figure 4

Percentage choice of S1 as a function of trial number (in blocks of 5 trials) averaged over Sessions 61–80. Half of the pigeons in Groups 5 and 10 were shifted to 1.5-s ITI s (from 5 and 10 s to 1.5 s) while the remaining pigeons in those groups stayed with 5- and 10-s ITIs, respectively, and the pigeons from Group 1.5 continued to have 1.5-s ITI s. Error bars = ±1 sem.

Figure 5

Percentage choice of S1 as a function of trial number for Trials 36–40 (immediately prior to the reversal) and Trials 41–45 (immediately after the reversal) averaged over Sessions 61–80 for Group 1.5, Groups 5 and 10 combined and for the pigeons transferred from Groups 5 and 10 to Group 1.5 (Trans to 1.5-s ITI). Error bars = ±1 sem.

Figure 6

Percentage choice of S1 as a function of trial number plotted separately for each point of reversal in the session for Group 1.5 (top), pigeons from Groups 5 and 10 that were transferred to 1.5-s ITIs (middle), and the pigeons from Groups 5 and 10 combined (bottom) that remained in the same ITI condition.