UUCF Summer RE 2011 Brain Glitches Session 4: Prisoner’s Dilemma

Prisoner’s Dilemma One of the classic examples of “game theory” A simple game with strategies that are anything but simple, and which we can use to help understand the way human brains work.

The Story Two people rob a bank together. They promise each other not to say anything to the police about their accomplice if captured. The police catch and arrest them. They think they have the right suspects but have no specific evidence against them. The suspects are put in separate rooms for interrogation.

Each suspect is given a choice: Squeal – Tell the police everything he knows about his accomplice. (Defect) Or Stay silent – Tell the police nothing and honor the promise made to the other thief. (Cooperate)

The possible outcomes Both suspects stay silent. The police have no evidence and both suspects walk, but remain under suspicion. Both suspects squeal. They share the blame for the crime, and both serve moderate prison sentences. One suspect squeals. He receives a full pardon, and the other suspect takes all the blame and receives a long prison sentence.

The Game rules Two players, each with a choice. C: Cooperate Or D: Defect Each player makes their choice in secret, without discussing it with the other player. Then the choices are revealed simultaneously Points will be awarded in M&M’s

Possible results Both players Cooperate. Each player receives 3 points. Both Players Defect. Each player receives 1 point. One player Defects and the other Cooperates. The Defecting player receives 5 points, and the Cooperating player receives 0

Opponent picks You Pick CooperateDefect Cooperate 30 Defect 51 Prisoner’s Dilemma - scoring

Possible variations Play one round and stop. Play a preset number of rounds. Play a number of rounds, but the players will not know in advance how many rounds there will be.

Now let’s play!

What’s going on? What’s the best strategy for the benefit of the group as a whole? What’s the best strategy for any one individual? Is there a perfect strategy for playing repeated rounds? Would the results be different if the players could talk to each other?