De Gustibus Disputare: Hyperbolic delay discounting integrates five approaches to impulsive choice

Impulsiveness is the tendency to shift preference from a better, later option to a poorer, earlier option as the two get closer. Explanations have extrapolated from five piecemeal elements of psychology – failure of cognitive rationality, Pavlovian conditioning, force of habit, incentive salience, and long chains of secondary reward – but in doing so have created models that stretch the properties of these elements as observed in the laboratory. The models are hard to integrate with each other, much less with the utility-maximizing structure of microeconomics. The increasing prominence of addictions, particularly addictions that do not involve a substance, have confronted behavioral science with these shortcomings. I suggest that the roles of all five phenomena follow from the hyperbolic discounting of expected reward: rationality can be seen as maximizing expected discounted reward as seen at a distance, which can be approximated by making choices in bundles; Pavlovian conditioning reduces to reward learning when a very short-term rewarding effect of conditioning stimuli is factored in; ‘habit’ subsumes various kinds of reward-seeking, especially that which has been narrowed by failures of self-control; incentive salience is a kind of short-term reward; self-reward is possible – and probably common – without being secondary to inborn turnkeys, limited rather by not being occasioned so often that the appetite(s) for it fail to build up.