Ephemeral reward task: Why is it so difficult for pigeons to learn it?

In the Ephemeral Reward Task, a subject is presented with a choice between two stimuli, A and B. If it chooses A, it gets a reward and the trial is over. If it chooses B, it gets a reward and it can then respond to A, to obtain a second reward. Wrasse (cleaner fish) and parrots learn to choose B optimally within 100 trials, primates may also learn, whereas pigeons and rats do not. We attempted to determine why pigeons have difficulty learning their task. First, we tested the hypothesis that pigeons fail because the outcome after choice of A is similar to the outcome after a response to A given choice of B. For group AC, after the choice of B, stimulus A changed to stimulus C. For group BC, after the choice of stimulus B, stimulus B changed to stimulus C. For group BB, after the choice of stimulus B, stimulus B remained for a second reward. None of the three groups learned to choose optimally. In Experiment 2, the probability of reward for choice of stimulus A or B was reduced to 50%. Pigeons learned to choose optimally. We suggest that the difference in value between one and two rewards may not be as great as the difference in value between 0.5 and one reward. (PsycInfo Database Record (c) 2025 APA, all rights reserved).