  What is intuitive: pro-social or anti-social behaviour? To answer this
fundamental question, recent studies analyse decision times in game theory
experiments under the assumption that intuitive decisions are fast and that
deliberation is slow. These analyses keep track of the average time taken to
make decisions under different conditions. Lacking any knowledge of the
underlying dynamics, such simplistic approach might however lead to erroneous
interpretations. Here we model the cognitive basis of strategic cooperative
decision making using the Drift Diffusion Model to discern between deliberation
and intuition and describe the evolution of the decision making in iterated
Prisoner's Dilemma experiments. We find that, although initially people's
intuitive decision is to cooperate, rational deliberation quickly becomes
dominant over an initial intuitive bias towards cooperation, which is fostered
by positive interactions as much as frustrated by a negative one. However, this
initial pro-social tendency is resilient, as after a pause it resets to the
same initial value. These results illustrate the new insight that can be
achieved thanks to a quantitative modelling of human behavior.
