The Ephemeral-Reward Task: Optimal Performance Depends on Reducing Impulsive Choice

摘要

The ephemeral-reward task involves providing subjects a choice between two distinctive stimuli, A and B, each containing an identical reward. If A is chosen, the food associated with A is obtained and the trial is over. If B is chosen, the food associated with B is obtained, but the food associated with A can be obtained as well. Thus, the food-maximizing solution is to choose B first. Although cleaner fish (wrasse) and parrots easily acquire the optimal response, choosing B, several primate species, as well as rats and pigeons, do not. To account for these paradoxical findings, we hypothesized that certain species do not associate the choice and reinforcement with the second reinforcement because they often respond impulsively to the seemingly equal, initial choice. To test this hypothesis, we 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 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, paradoxically, allow for optimal task performance. The general implications of this finding are discussed.