Given the rapid proliferation of advanced information technologies, including the Internet, modern humans can easily access vast amount of socially transmitted information. Intuitively, this situation is isomorphic to some eusocial insects that are known to solve the exploration-exploitation dilemma collectively through information transfer (e.g., honeybees [Seeley et al., 1991]; and ants [Shaffer, Sasaki & Pratt, 2013]). Yet, in contrast from the eusocial insects, whose colonies are composed of kin, human collective performance may be affected by an inherent free-rider problem [Bolton & Harris, 1999; Kameda, Tsukasaki, Hastie & Berg, 2011]. Specifically, in groups involving non-kin members, it is expected that free-riders, who allow others to search for better alternatives and then exploit their findings through social learning ("information scroungers"), will frequently appear, and consequently undermine the advantage of collective intelligence [Rogers, 1998; Kameda & Nakanishi, 2003].