Left: probability of switching to another strategy depending on the payoff differences for both the spatial and non spatial experiment. The payoff difference is between the focal player and the best player of the opposite strategy. The results are consistent with imitating the neighbors with higher payoffs. However this imitation is not unconditional, but the higher the payoff difference the larger is the probability of imitation. In addition, players might spontaneously switch their strategies even if they have no neighbors playing the other strategy, resembling mutations. Error bars are the standard deviations of a binomial distribution,

, where

is the number of samples and

is the probability of changing the action). Right: Probability of mutations in time. Mutations are defined as the probability that a cooperator surrounded by four cooperators would change the strategy in the next round or that a defector surrounded by four defectors will change the strategy in the next round. We see a large number of mutations, which decreases over time, but always stay substantial. Again in both treatments the players show a similar pattern of behavior. Error bars are the standard deviations of a binomial distribution,

, where

is the number of samples and

is the probability of mutation).

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