Exploring decoy effects on computerized task preferences in rhesus monkeys (Macaca mulatta).

Abstract

Citation-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.05.02.06.2018 Note: This paper is the final report based on an accepted peer-reviewed preregistered submission that can be found here. Abstract-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. Choice behavior reveals a wealth of information regarding one's preferences, perceptions, thoughts, and ideas, and, of equal importance, the factors that impact decision-making. To this latter point, choice behavior does not occur in a vacuum. Rather, choices are largely context-dependent in terms of the environment in which decisions are made. One clear example of context-dependent choice behavior that is prevalent across a variety of domains and includes a growing number of species is the asymmetric dominance effect (ADE), also referred to as the decoy effect (for a review, see Huber, Payne, & Puto, 2014). In the decoy effect, a decision-maker chooses among two options that differ on multiple dimensions and the relative preference between original options is altered following the introduction of a third weaker option (the decoy). In the original choice set, the first option (e.g., an expensive 5-star restaurant) dominates the second option (e.g., a less-expensive 3-star restaurant) on one dimension