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"Palmagatchi"   (Summer 2005)



Tit for Tat Game Instructions

Playing the Game

This game is based on the problem of the Prisoner's Dilemma. You have the choice of cooperating with their partners or defecting against them. Depending on what both you and your partner do, the payoffs are different. In the standard game, the payoffs are as follows:

   Defect Cooperate
Defect  1  5
Cooperate  0  3

Start the game by entering your name in the start screen (see the general instructions page). When you start the game you will find a screen that reports your score, last play, results of your last exchange and your predominant strategy. There are also buttons at the bottom marked for Cooperate and Defect. To play, choose one of the two strategies and hit the Hide button, which will make your decision choice disappear from site. You can meet other players by lining up your Palms and having ONE player hit the Meet button (one person is the sender and the other is the receiver). The machines will then display the results of your interaction and update your display accordingly. At any point in time you can hit the show button to make the Cooperate and Defect buttons reappear so that you can change your decision. The left/right positioning of the choices is randomized so that your partner can't tell your decision by the side that you click on. The game is over when one player gets to a set score (25 or 50 usually).

Game Parameters

Unlike the other games, players have access to changing the preferences themselves. Players can view the current preferences when they are playing the game by going to the menu in the upper left and choosing view preferences. To change the preferences you will need to go to the main screen where you enter your name and choose Set Preferences from the menu in the upper left. From this screen you can change the payoffs from each of the four possible meetings by clicking on the number that you want to change and then clicking the up or down adjust arrows.

You can also change some other parameters as follows:

  • Force consecutive meetings - Choosing a number greater than one here will require a player to play multiple games with a given player before moving on to the next player.
  • Limit to first opponents - Choosing a number for this parameter will limit the number of different opponents that one player can compete against. Whoever the first n opponents are will be the only people that the player can interact with, though they can repeatedly interact with those players.
  • Show Last Played - Shows the last strategy played on the screen
  • Show Predominant Play - Show your predominant strategy on the screen.

Information for Instructors

This game can be played on many different levels - from a simple problem about cooperating in communities to a more complex discussion of game theory. The key to the game is creating scenarios under which cooperation can persist. Usually we start out with the default values shown above, and often defectors win. Then we try having everyone force 3-5 consecutive meetings and see what happens. You can try various combinations of the different parameters to see what strategies people come up with.

Discussion in the end can be based on evolution of cooperation, community formation, game theory, or related systems.



MIT Teacher Education Program