Shigehito Tanida & Toshio Yamagishi Hokkaido University

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 • Our Question: • Why do people cooperate in one-shot PD games with an unrelated partner? • 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. • Weexamine the validity of explanation of cooperation in one-shot PD, analyzing relationship between the subject’s attention to the matrix and their decision.

3. Two alternative explanationsof cooperation in one-shot PD game • Utility transformationexplanation • 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 • Social Exchange Heuristicexplanation • 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 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. 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.

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

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

7. If the Heuristicexplanation 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. 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.

8. Proportion of the fixation Cooperators C Defectors D .38 C .25 C D .23 C .21 .21 D .16 .32 D .25 Result1: Cooperation rate & Proportion of the fixation • Cooperation rate Simple Matrix Condition: 44.8% Complex Matrix Condition: 36.7% (χ2(1)=0.30, n.s.）

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

10. Proportion of fixation inSimple Matrix condition C D .27 C .22 D .28 .24 Defectors Cooperators • Proportion of fixation inComplex Matrix condition C C D D .39 .38 C C .21 .27 C D .17 C .20 .21 .21 D D .21 .13 .37 D .26 Cooperators Defectors

11. Discussion • The result of Defectors’ attention in ComplexMatrix Condition indicated that players’ social motivation plays an important role in the situation that is lackingthe 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.