高橋泰城准教授らの論文が『Journal of the Physical Society of Japan』に公刊されました

Hino, M., Irie, Y., Hisakado, M., Takahashi, T ., & Mori. S. (2016). Detection of Phase Transition in Generalized Pólya Urn in Information Cascade Experiment. Journal of the Physical Society of Japan, 85, 3, 034002.

Abstract

We propose a method of detecting a phase transition in a generalized Pólya urn in an information cascade experiment. The method is based on the asymptotic behavior of the correlation C(t) between the first subject’s choice and the t + 1-th subject’s choice, the limit value of which, c≡limt→∞C(t), is the order parameter of the phase transition. To verify the method, we perform a voting experiment using two-choice questions. An urn X is chosen at random from two urns A and B, which contain red and blue balls in different configurations. Subjects sequentially guess whether X is A or B using information about the prior subjects’ choices and the color of a ball randomly drawn from X. The color tells the subject which is X with probability q. We set q∈{5/9,6/9,7/9,8/9} by controlling the configurations of red and blue balls in A and B. The (average) lengths of the sequence of the subjects are 63, 63, 54.0, and 60.5 for q∈{5/9,6/9,7/9,8/9}, respectively. We describe the sequential voting process by a nonlinear Pólya urn model. The model suggests the possibility of a phase transition when q changes. We show that c > 0 (= 0) for q=5/9,6/9 (7/9,8/9) and detect the phase transition using the proposed method.

PDF paper download here: http://journals.jps.jp/doi/full/10.7566/JPSJ.85.034002

高橋伸幸准教授、小野田竜一専門研究員の論文が『心理学研究』に公刊されました

小野田竜一・高橋伸幸 (2016). 2つの集団で構成される社会で一般交換を維持させる利他行動の特徴ー心理学研究, 87, 240-250.

Abstract

Previous studies on generalized exchange have argued that group plays an important role in the emergence of cooperative society. To examine to what extent the role of a group is important, we conducted computer simulations in which players decide whether to give resources to members of a society composed of two groups. We examined whether a society consisting of any of the possible conceivable strategies (65536 strategies total) could resist invasion by an unconditional defector (ALLD) and an unconditional cooperator (ALLC). The results showed that universalist strategies, which give resources to both in-group members and out-group members equally, and in-group favoring strategies, which give resources to in-group members more than outgroup members, could resist invasion. Furthermore, we found that in-group favoring strategies could exclude ALLC from the circle of resource flow more easily than universalist strategies. These results imply that it may be necessary to employ an in-group favoring strategy that utilizes the group membership information of other people in order to maintain generalized exchange in a society composed of two group

PDF paper download here: https://www.jstage.jst.go.jp/article/jjpsy/advpub/0/advpub_87.14080/_article/-char/ja/

カヴァナ客員研究員のエッセイがデジタルマガジン『aeon』に掲載されました

Kavanagh, C. (2016,May). Did Easter Island culture collapse? The answer is not simple. Aeon Magazine. Retrieved from https://aeon.co/ideas/the-easter-island-controversy-has-no-single-simple-answer

Click here to read the article: https://aeon.co/essays/can-religion-be-based-on-ritual-practice-without-belief