Researchers explain how to win the game rock-paper-scissors, sort of

HANGZHOU, China, May 2 (UPI) -- If the game rock-paper-scissors were played by random number generators, or robots, there would never be any way to game the system. Each robotic player would randomly throw out one of the three signs, and over a long enough sample sizes, the games would be equally split between wins for player A, wins for player B and ties.

But rock-paper-scissors is rarely played by robots. More often, it's played by humans -- humans that operate emotionally, even irrationally. And humans playing rock-paper-scissors, as researchers from Zhejiang University in China recently showed, often follow a predictable pattern -- the "win-stay lose-shift" strategy.

Researchers recruited several hundred students to play in a tournament of rock-paper-scissors featuring cash prizes (so as to incentivize genuine competition). In studying the games, strategies and patterns, researchers noticed that after a contestant won a round, they were much more likely to stick with the same symbol, whereas losers were more likely to switch to one of the other two.

In theory, a good player should employ game theory: randomizing their choices to remain unpredictable. Two players employing game theory tactics would essentially cancel each other out, each with equal probability to win -- a reality known as the Nash equilibrium.

But, as the researchers found out, humans often fail to employ such tactics.

"The game of rock-paper-scissors exhibits collective cyclic motions which cannot be understood by the Nash equilibrium concept," explained researchers.

"Whether conditional response is a basic decision-making mechanism of the human brain or just a consequence of more fundamental neural mechanisms is a challenging question for future studies," the study's authors added.