"The human mind is built for approximations," begins Jerald Kralik in a paper published October 3, 2012 in the Public Library of Science (PLoS). "While useful in many situations, this … can lead to apparently irrational decision-making."
Kralik is an assistant professor in the Department of Psychological and Brain Sciences at Dartmouth, and his co-authors include graduate student Eric Xu, Sara Khan '08, who worked in Kralik’s lab as an undergraduate and then as a research assistant after she graduated, previous research assistant Emily Knight, and William Levine '11, who spent his four undergraduate years working in Kralik's lab.
"Like humans, monkeys can make irrational decisions when making choices. When making decisions about the value of an assortment of different objects, people approximate an average overall value, which though frequently useful can lead to apparently irrational decision-making," writes the PLoS in its summary announcement.
The paper cites studies in which people demonstrated a willingness to pay more for a small set of high-quality goods than for the same set of high-quality goods with lower-quality items added. To test whether this kind of choice behavior could also be seen in other primates, Kralik and his team carried out both laboratory and field experiments using rhesus macaque monkeys.
The monkeys were first presented with a highly prized fruit (e.g., a grape) or a less-prized vegetable (e.g., a green bean). When each item was offered alone, the monkeys readily accepted and ate them. Then the monkeys were offered a choice between one piece of fruit alone and a larger amount of food in which the same piece of fruit was paired with the vegetable. While the paired option constituted a larger meal, the macaques chose the smaller, fruit-only meal. In other words, the monkeys chose the option with the higher average value (one piece of fruit alone) rather than the higher overall value (same piece of fruit with a vegetable).
In these experiments, Kralik and his Dartmouth group showed for the first time that both human and non-human primates follow similar decision-making routines that may not necessarily be rational. Kralik sees these shared behaviors as a "way of simplifying the world around us, making choices easier, sometimes at the expense of 'rationality.'"