Vol 5, Issue 2, May 2018

Preregistered Report: Exploring Decoy Effects on Computerized Task Preferences in Rhesus Monkeys (Macaca mulatta)


Parrish, A. E., Afrifa, E., & Beran, M. J. (2018). Exploring decoy effects on computerized task preferences in rhesus monkeys (Macaca mulatta). Animal Behavior and Cognition, 5(2), 235–253. https://doi.org/10.26451/abc.


The asymmetric dominance effect or decoy effect emerges when a third inferior option is introduced to a choice set. The decoy option, although typically not chosen, impacts relative preference for the original two options. This decisional bias stands in contrast with rational choice theory, which dictates that choice behavior should remain consistent for the original options with the addition of different alternatives to a choice set such as the decoy. In the current study, we assessed the decoy effect in rhesus monkeys using a computerized task battery that introduced two different computerized tasks, including a matching-to-sample task and a psychomotor task called PURSUIT. Decoy tasks were designed such that they were inferior versions of these original task options, requiring longer time to completion (via slowed cursor speeds) and subsequently reduced reinforcement rates. Monkeys learned to associate unique icons for each task (including for decoy tasks), and used these icons to select their preferred task from a choice set of two to three task options. Monkeys learned to perform all tasks, but did not show evidence of the decoy effect using this task preference paradigm. We discuss the role of initial task preference (and task biases), task type (symbolic vs. perceptual), and decoy effect sizes in light of these findings. We contrast the current results to previous findings of the decoy effect in rhesus monkeys using a perceptual paradigm as well as to other evidence of the decoy effect in non-primate animal species.


Decoy effect, Asymmetric dominance effect, Decision-making, Rhesus monkeys