2013年10月1日火曜日

Thirst-dependent risk preferences in monkeys identify a primitive form of wealth

Hiroshi Yamada, Agnieszka Tymula, Kenway Louie, and Paul W. Glimcher
PNAS September 9, 2013

「サルは(ヒトと違って)リスク愛好的だ」と信じられていたが、実験課題について十分に訓練したら、サルもヒトと同様にリスク回避的だった。
http://www.pnas.org/content/early/2013/09/04/1308718110

サルのリスク下の意思決定(報酬は水)。
十分なトレーニングを積むことで、(ヒトと同様に)合理的な選択を行う事ができ、ややリスク回避的。
また、喉が乾いているときは、よりリスク回避的になる。

Experimental economic techniques have been widely used to evaluate human risk attitudes, but how these measured attitudes relate to overall individual wealth levels is unclear. Previous noneconomic work has addressed this uncertainty in animals by asking the following: (i) Do our close evolutionary relatives share both our risk attitudes and our degree of economic rationality? And (ii) how does the amount of food or water one holds (a nonpecuniary form of “wealth”) alter risk attitudes in these choosers? Unfortunately, existing noneconomic studies have provided conflicting insights from an economic point of view. We therefore used standard techniques from human experimental economics to measure monkey risk attitudes for water rewards as a function of blood osmolality (an objective measure of how much water the subjects possess). Early in training, monkeys behaved randomly, consistently violating first-order stochastic dominance and monotonicity. After training, they behaved like human choosers—technically consistent in their choices and weakly risk averse (i.e., risk averse or risk neutral on average)—suggesting that well-trained monkeys can serve as a model for human choice behavior. As with attitudes about money in humans, these risk attitudes were strongly wealth dependent; as the animals became “poorer,” risk aversion increased, a finding incompatible with some models of wealth and risk in human decision making.

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