Roberts Gilbert, Renwick James S
School of Biology, University of Newcastle upon Tyne, Henry Wellcome Building, Newcastle upon Tyne NE2 4HH, UK.
Proc Biol Sci. 2003 Nov 7;270(1530):2279-83. doi: 10.1098/rspb.2003.2491.
Pairs of individuals frequently face situations in which they could do well if they cooperated, but each risks being exploited. The Prisoner's Dilemma is widely used for investigating such scenarios, but it is framed in terms of cooperating and defecting, whereas in reality cooperation is rarely "all or nothing". Recent models allowing for variable investment in cooperation indicated the success of a strategy of "raising-the-stakes" (RTS), which invests minimally at first and then increases its investment if its partner matches it. We tested whether this strategy was adopted by subjects participating in an experiment in which they could choose how much money to give to a partner, reciprocity being encouraged by doubling donations. Subjects did increase their donations over successive rounds, both when playing against a stooge who reciprocated with the same investment, and when playing with a partner who was free to choose their investment. Subjects showed a strong tendency to match variations in their partner's investments. Cooperation was therefore achieved through a combination of initial escalation (RTS strategy) and quantitative responsiveness ("give-as-good-as-you-get" strategy). Although initial offers were higher than predicted, our results were broadly consistent with theoretical expectations.
如果他们合作，就能取得良好的结果，但每个人都有被对方利用的风险。囚徒困境被广泛用于研究此类情景，但其设定是关于合作与背叛，而在现实中合作很少是“全有或全无”的。最近允许对合作进行可变投资的模型表明了“提高赌注”（RTS）策略的成功，该策略一开始投资极少，然后如果其伙伴也进行同样投资，它就增加投资。我们测试了参与一项实验的受试者是否采用了这一策略，在该实验中他们可以选择给伙伴多少钱，通过将捐赠翻倍来鼓励互惠。受试者在连续几轮中都增加了他们的捐赠，无论是与以相同投资进行互惠的傀儡玩家对战时，还是与可以自由选择投资的伙伴对战时。受试者表现出强烈的倾向，即与伙伴投资的变化相匹配。因此，合作是通过初始升级（RTS策略）和定量响应（“一报还一报”策略）的结合来实现的。尽管初始报价高于预期，但我们的结果与理论预期大致相符。
