RESUMEN
In a midsession reversal task, the session begins with a simple simultaneous discrimination in which one stimulus (S1) is correct and the other stimulus (S2) is incorrect (S1+/S2-). At the midpoint of the session, the discrimination reverses and S2 becomes the correct choice (S2+/S1-). When choosing optimally, a pigeon should choose S1 until the first trial in which its choice is not reinforced and then it should shift to S2 (win-stay/lose-shift). With this task, pigeons have been shown to respond suboptimally by anticipating the reversal (making anticipatory errors) and continuing to choose S1 after the reversal (making perseverative errors). This suboptimal behavior may result from a pigeon's relative impulsivity due to the immediacy of reinforcement following choice. In other choice tasks, there is evidence that the introduction of a short delay between choice and reinforcement may decrease pigeons' impulsivity. In the present experiment, a delay was introduced between stimulus selection and reinforcement to assess whether it results in a decrease in anticipatory and perseverative errors. Pigeons that had a delay between choice and reinforcement were a bit slower in acquiring the midsession reversal task compared to those without a delay, but showed no decrease in either anticipatory or perseverative errors. It is likely that the pigeons' natural tendency to use time from the start of the session to the reversal as a cue to reverse prevented the delay from increasing accuracy on this task.