We used an online ball-tossing game called Cyberball [38] to manipulate ostracism. We used Cyberball played by four people. Participants, who did not know each other, were told that they were playing the game with three other players in the same room who were also participating in this experiment. In reality, the computer controlled the three agents involved in the game. Participants were informed that they would be represented by an animated hand at the bottom of the screen whereas the other three players would be represented by animated figures located above and to the left, right and opposite side of the participant's animated hand. When the ball was tossed to the participants, they were instructed to press “1” to throw the ball to the left player, “2” to the opposite player, and “3” to the right player by using a key board. In a practice session, participants were thrown the ball roughly one fourth of the time by the other “players” in both the ostracism and the inclusion conditions. In an experimental session, participants assigned to the ostracism condition experienced that they and the opposite player received the ball twice at the beginning of the game, and for the remaining time, never received the ball again. Participants assigned to the inclusion condition received the ball one fourth of the time from the other “players” like in the practice session. The game ended after 10 throws in the practice session and 40 throws in the experimental session. It lasted approximately five minutes.

Recommendation game.

We developed a recommendation game based on the ultimatum game [39] to assess how people interact with others who attempt retaliation. This game was also played by four players like Cyberball. In reality, all other players were controlled by the computer. One round of the game consisted of the following procedures. First, the computer randomly assigned one player as a proposer, another player as a responder, and the other two players as recommenders. Next, the proposer decided how to divide 1000 points with the responder by choosing a multiple of 100 as the amount which the proposer would continue to hold. After that, the responder tentatively decided whether to accept or reject this offer. If the responder accepted the offer, the points were distributed in accordance with the offer. If the responder rejected the offer, neither the proposer nor responder received anything. On the basis of the responder's tentative decision, the recommenders recommended whether the responder should accept or reject the offer. Given these recommendations, the responder finally decided whether to accept or reject the offer. In accordance with this final choice, the points were distributed.

Participants took part in 12 rounds: three as the proposer, three as the responder, and six as the recommender. They were told that all decision had to be made within 15 seconds. Each player's decision was only known to players who made decisions after that in a round. Specifically, the proposer could not know any decision made by the responder or recommenders, the responder could know all decisions, and the recommender could know the proposer's decision and responder's first decision. Participants were told that the responder's second decision was not known to other players until the end of the game. They were informed that the points they received during the game were exchanged for an extra reward up to 500 yen (about US$5) in accordance with an absolute amount of the points. In actuality, all participants received 500 yen as an extra reward regardless of their decisions in addition to 500 yen as a basic reward.

We set the following situation to assess how people interacted with others who attempt retaliation. First, participants were assigned to the recommender, and the proposer (the left or right player, who was the ostracizer in the ostracism condition) offered the responder (the opposite player, who was the victim in the ostracism condition) 400 points out of 1000. This offer could be regarded as fair [40]–[42]. Next, the responder chose “reject” to this offer. This behavior could be conceived as retaliation by preventing the proposer from obtaining additional points [42]–[44]. The next participant's decision as the recommender was the target for assessment as correlates of participant's trait EI. If the participant recommended that the responder should accept the offer, this behavior would make the responder realize that accepting the offer was more rational because the offer was quite fair and the responder could increase his/her points. We used whether participants recommended that the responder should accept the offer in this situation as the behavioral measure of regulating emotions in others who attempt retaliation.

To make participants believe they played with real participants, they also completed not only rounds of the above situation but also following situations (e.g., participants were assigned to be the proposer or the responder). 1: When both participants and the opposite player were assigned to the recommender, the proposer (the left or right player) offered the responder (the right or left player, respectively) 400 points out of 1000. The responder selected “accept” for this offer. 2: When the participants and the opposite player were assigned as the recommender and proposer, respectively, the opposite player offered the responder (the left or right player) 800 points out of 1000. The responder selected “reject” for this offer. 3: When the participants and the opposite player were assigned to the responder and recommender, respectively, the proposer (the left or right player) offered the participants 400 points out of 1000. Following the participants' first decision, the opposite player recommended “reject” and the other recommender (the right or left player, respectively) recommended “accept” to the participants. 4: When the participants and the opposite player were assigned to the responder and proposer, respectively, the opposite player offered the participants 400 points out of 1000. Following the participants' first decision, the left player recommended “accept” and the right player recommended “reject” to the participants. 5: When the participants were assigned to the proposer, they first decided the offer. After that, they did not know what choice the other players had selected. How other people behaved was determined considering that the opposite player attempted to cause the left and right players to lose and the left and right players mostly behaved fairly. We also analyzed the participant behaviors in these other rounds as dependent variables, though they were not main aim of this study. We found no significant relationship between trait EI and these behavioral measures.

The order of completing these rounds was randomly assigned to each participant. The game ended after participants completed all 12 rounds. It lasted approximately 15 minutes.