Movies, vacations, and meals are all examples of events composed of a sequence of smaller events. How do we go from our evaluations of each scene in a movie to an evaluation of the sequence as a wholeα In theory, we should simply average the values of the individual events. In practice, however, we are biased towards sequences where each element tends to be better than the previous, where the last value is large, and we overweight the best (or worst) part of the sequence. To study how general these biases are we examined monkeys' preferences for sequences of rewards in a novel reward repeat task. Monkeys were first given a sequence of rewards and then chose between repeating the sequence or receiving a standard comparator sequence. We found that, like humans, monkeys overweight events that happen later in a sequence, so much so that adding a small reward to the end of a sequence can paradoxically reduce its value. Monkeys were also biased towards sequences with large peak values (the highest value in the sequence), but only following a working memory challenge, suggesting that this preference may be driven by memory limitations. These results demonstrate the cross-species nature of biases in preferences for sequences of outcomes. In addition, monkeys' consistent preference for sequences in which large values occur later challenges the generality of discounting models of intertemporal choice in animals.
Bibliographical noteFunding Information:
We thank Marc Mancarella, Mariah Meyer, Meghan Castagno, Evan Alter, and Alberto Sepulveda for help in data collection. We thank John Pearson (Duke University) for help with statistics. This research was supported by a K99/R00 from the NIH (DA027718) and a Sloan Foundation fellowship to BYH.
- Intertemporal choice