Vol 5, Issue 1, February 2018

The Ephemeral Reward Task: Pigeons and Rats Fail to Learn Unless Discouraged from Impulsive Choice


Zentall, T. R., Case, J. P., Berry, J. R., & Luong, J. (2018). The ephemeral reward task: Pigeons and rats fail to learn unless discouraged from impulsive choice. Animal Behavior and Cognition, 5(1), 169-180. https://doi.org/10.26451/abc.


The failure of certain species to learn a particular task while others learn it easily can help identify the learning mechanisms involved. In the ephemeral reward task, animals are given a choice between two distinctive stimuli, A and B, each containing an identical bit of food. If they choose A they get the food on A and the trial is over. If they choose B they get the food on B and they are allowed to get the food on A before the trial is over. Thus, it is optimal to choose B. Although cleaner fish (wrasse) and parrots acquire the optimal response easily, several primate species do not. Furthermore, pigeons and rats also appear to be unable learn to choose optimally. The failure of primates, pigeons, and rats to learn this task and the ease with which cleaner fish and parrots learn it raises important questions about the learning mechanisms involved in those differences. To account for these paradoxical findings, we proposed that certain species may have difficulty with this task because they tend to respond impulsively to the initial choice which has similar immediate outcomes and they do not associate the choice and reinforcement with the second reinforcement. To test this hypothesis, we temporally separated the initial choice from the first reinforcement by imposing a 20-s delay between the choice and its outcome. Under these conditions both pigeons and rats gradually acquired the optimal choice response. We suggest that impulsive choice may make it difficult to acquire certain tasks and imposing a delay between choice and outcome may decrease impulsivity and allow for closer to optimal task performance.


Ephemeral choice task, Suboptimal choice, Prior commitment, Delay of reinforcement