Source: http://www.technologyreview.com/view/527...

The results reveal a surprising pattern of behavior. On average, the players in all the groups chose each action about a third of the time, which is exactly as expected if their choices were random.

But a closer inspection of their behavior reveals something else. Zhijian and co say that players who win tend to stick with the same action while those who lose switch to the next action in a clockwise direction (where R → P → S is clockwise).

This is known in game theory as a conditional response and has never been observed before in Rock-Paper-Scissors experiments. Zhijian and co speculate that this is probably because previous experiments have all been done on a much smaller scale.

“This game exhibits collective cyclic motions which cannot be understood by the Nash Equilibrium concept but are successfully explained by the empirical data-inspired conditional response mechanism,” say Zhijian and co.

In fact, a “win-stay, lose-shift” strategy is entirely plausible from a psychological point of view: people tend to stick with a winning strategy.