Delay or probability discounting in a model of impulsive behavior: Effect of alcohol

Little is known about the acute effects of drugs of abuse on impulsivity an d self-control. In this study impulsivity was assessed in humans using a co mputer task that measured delay and probability discounting. Discounting de scribes how much the value of a reward (or punisher) is decreased when its occurrence is either delayed or uncertain. Twenty-four healthy adult volunt eers ingested a moderate dose of ethanol < 0.5 or 0.8 g/kg ethanol; n = 12 at each dose) or placebo before completing the discounting task. In the tas k the participants were given a series of choices between a small, immediat e, certain amount of money and $10 that was either delayed (0, 2, 30, 180, or 365 days) or probabilistic (i.e., certainty of receipt was 1.0, .9, .75, .5, or .25). The point at which each individual was indifferent between th e smaller immediate or certain reward and the $10 delayed or probabilistic reward was identified using an adjusting-amount procedure. The results indi cated that (a) delay and probability discounting were well described by a h yperbolic function; (b) delay and probability discounting were positively c orrelated within subjects; (c) delay and probability discounting were moder ately correlated with personality measures of impulsivity; and (d) alcohol had no effect on discounting.