The relative value of two options for pigeons depends on their context

It is well known that when humans are given a choice between two options, their preference is affected by the presence of a third. Generally, there is an increase in preference for the option closer to the third. We show that a shift in preference in the direction away from the third option can occur in animals. We gave pigeons a choice between A, reinforcement following 10 pecks and a 0.5-s delay, and B, reinforcement following 5 pecks and a 1.5-s delay. Once stable preferences were established, we introduced a third stimulus, less preferred than the other two: C, reinforcement following 20 pecks and a 0.5-s delay or D, reinforcement following 5 pecks and a 4.5-s delay. We found that pigeons presented with C showed an increased preference for B, whereas pigeons presented with D showed an increased preference for A. Our results were consistent with the similarity or attentional hypothesis, which suggests that the third option should interfere with the option more similar to it or would draw attention to the less preferred component of the third option and generalize to the option more similar to it. Possible accounts for the differences in outcomes are suggested.The authors would like to thank the students who helped to conduct the experiment. This work was supported by a Portuguese Foundation for Science and Technology (FCT) Doctoral Grant (SFRH/BD/78566/2011) to Carlos Pinto and a FCT Doctoral Grant (SFRH/BD/77061/2011) to Ines Fortes.