1. Where to look and why? : Utility and heuristics as explanations of cooperation in one-shot PD games Shigehito Tanida & Toshio Yamagishi Hokkaido University

2. Overview We measured subject’s eye movements via an eye camera while Ss were looking at the matrix and making a decision in one- shot PD game. We examine the validity of explanation of cooperation in one-shot PD, analyzing relationship between the subject’s attention to the matrix and their decision. Our Question: Why do people cooperate in one-shot PD games with an unrelated partner?

3. Two alternative explanations of cooperation in one-shot PD game 1. Utility transformation explanation – Social Value Orientation (SVO) (e.g., van Lange, 1999): Utility of an outcome in a social exchange (e.g., PD game) is a combination of 1. Utility of own outcome 2. Utility of partner’s outcome 3. Disutility of inequality of the two players’ outcomes Cooperators (Pro-Socials) are expected to pay more attention to the partner’s outcome than defectors. Defectors (Pro-Selfs) care only about their own outcome.

4. Two alternative explanations of cooperation in one-shot PD game 2.Social Exchange Heuristic explanation Whether one cooperates or defects depends on how he/she define the game situation. In this approach, players’ decisions depend not so much on the utilities of outcomes but rather on activation of a particular heuristic SEH:A default decision rule in a social exchange that minimizes a particular type of error When activated by cues of being in a social exchange, it makes people seek mutual cooperation while avoiding being a sucker.  When activated by cues of being in a social exchange, it makes people seek mutual cooperation while avoiding being a sucker. The relative plausibility of the two explanations will depend on how easy it is for the player to intuitively grasp the game as an incidence of social exchange. We conducted two condition that was manipulated the kind of intuitive sense of exchange.

5. Simple Matrix Condition The gain of mutual cooperation is easy to understand Cooperate Defect Own Partner 1200 1800 0 0 600 Subject Partner

6. It is difficult to intuitively grasp that it represents a social exchange Cooperate Defect Own Partner 1281 1839 165 1839 723 Subject Partner (simple payoff x.93) + 165 Complex Matrix Condition

7. Eye Movement Tracking We observed where in the PD matrix players looked at with an eye camera. If the utility transformation explanation is valid, In both condition, Cooperators should look at their partner’s payoffs (compared to own payoffs) more than Defectors. If the Heuristic explanation is valid, The cooperation rate and the proportion of fixation of mutual cooperation cell that Ss looked at in Simple Matrix condition should be higher than in the Complex Matrix Condition.

8. Result1: Cooperation rate & Proportion of the fixation Simple Matrix Condition: 44.8 % Complex Matrix Condition: 36.7 % ( χ 2 (1)=0.30, n.s. ） Cooperation rate Cooperators D.38.21.25.16 D C C Defectors.23.21.25.32 D D C C Proportion of the fixation

9. Which did Ss look at matrix? - Own or Partner's payoff? Cooperate Defect Own Partner 1200 1800 0 0 600 Subject Partner Result : Simple Matrix Condition Result : Complex Matrix Condition p<.05

10. D.38.21 D C C.17.20.26.37 D D C C Proportion of fixation in Complex Matrix condition Cooperators Defectors Proportion of fixation in Simple Matrix condition D.39.21.27.13 D C C.27.22.24 D D C C.28 Cooperators Defectors

11. Discussion The result of Defectors’ attention in Complex Matrix Condition indicated that players’ social motivation plays an important role in the situation that is lacking the kind of intuitive sense of exchange. Defectors in Simple Matrix Condition paid attention to the mutual cooperation cell, suggested that their decision is more likely to be driven by heuristics rather than transformed utilities.