When more means less: Factors affecting human self-control in a local versus global choice paradigm

Adult human participants experienced 200 trials in which they repeatedly ch ose between two immediately available rewards of different magnitudes (poin ts exchangeable for money). Although choosing the larger reward always resu lted in more points per trial, choosing the smaller reward increased the ma gnitude of both rewards on the next trial. Thus consistent choice of the sm aller reward resulted in a greater average number of points overall. This e ffect on global (overall) reinforcement rate was gradual and difficult to p erceive by comparison with the (opposed) difference in points between the t wo alternatives on a given trial (local rate). Participants generally prefe rred the larger reward and thus failed to maximize the global reinforcement rate. Preference for this higher local rate of reinforcement increased whe n the difference in local rates was larger. However, when the salience of t he global contingency was enhanced by providing cognitive or social compara tive information, participants chose the larger reward less often and thus increased global reinforcement rate. (C) 1999 Academic Press.