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    Rock-Paper-Scissors: Not So Random After All?
    By Gunnar De Winter | July 20th 2011 03:18 AM | 1 comment | Print | E-mail | Track Comments
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    Rock-paper-scissors (henceforth, it shall be known as RPS) is a game, or method to determine who has to do something nobody really wants to do. The rules are pretty well-known. The players simultaneously form a rock, paper or scissors gesture with their hands, and rock beats scissors beats paper beats rock. The same gesture results in a draw. Since one person’s win means the other one’s loss, it can be considered a zero-sum game. Players can only achieve optimal outcomes if they do not imitate each other.

    A recent study went looking for the occurrence of automatic imitation in games of RPS. Ever since the discovery of mirror neurons, ensuing research has shown that human beings often spontaneously imitate each other’s behavior. To address whether this also takes place in a strategic context where imitation is discouraged (winning could earn the participants money), the researchers compared the players’ performance under two conditions:

    •  One player blindfolded, and one sighted.

    •  Both players blindfolded.

    Since blindfolded players cannot see their opponents gesture, one would expect that, in the case of automatic imitation, the proportion of draws would exceed one third in the first condition, but not in the second one.

    And indeed, the study found that the proportion of draws was higher in the blind-sighted condition (see figure 1), but not in the blind-blind one, thereby suggesting that, in RPS, players seem to imitate their opponents, despite being discouraged to do so.

      

    Figure 1: Mean probabilities of gesture execution by the sighted person, given the gesture of the blindfolded player. (Source: Cook et al., 2011)

      

    The authors conclude that

    The draws effect observed in this experiment provides evidence that automatic imitation is ‘automatic’ in the sense of being very difficult to inhibit. Only by avoiding imitation could pairs maximize their chances of achieving the win bonus. Thus, players imitated their opponents' actions despite having a financial incentive to avoid imitation. More broadly, our results challenge the tendency in economic and game theory to ignore, or abstract away, the physical aspects of social interaction. The draws effects hows that physical factors are not only important in complicated strategic interactions, where strong emotional drivers such as fairness, trust and reputation play a role. Rather, the embodied aspects of cognition play a significant role even at the simplest level of game playing, and when they work against players' interests.

      

    Reference

    Cook, R.; Bird, G.; Lünser, G.; Huck, S. and Heyes, C. (2011). Automatic imitation in a strategic context: players of rock-paper-scissors imitate opponents’ gestures. Proceedings of the Royal Society B. doi: 10.1098/rspb.2011.1024. (full article here)

    Comments

    The Stand-Up Physicist
    My friend Dean at MIT would always crush Dave at RPS. Dave was some kind of grand master at chess, but Dean was skilled with reading people. I was 50-50 against both in the game because I practice at being random. I did avoid eye contact.