Evaluates previous round's payoffs. If in previous round, Pavlov received a "reward" (i.e. both Pavlov and partner cooperated), or a "temptation payoff" (i.e. Pavlov defected while partnercooperated), then Pavlov sticks with winning strategy. However, if Pavlov received a "punishment" in previous round (i.e. both Pavlov and partner defected) or a "sucker payoff" (Pavlov cooperated but partner defected), then Pavlov switches strategy.