Richards, J. B., Zhang, L., Mitchell, S. H., & de Wit, H. (1999).
Delay or probability discounting in a model of impulsive behavior: Effect of alcohol.
Journal of the Experimental Analysis of Behavior,
71, 121-143.
Little is known about the acute effects of drugs of abuse on
impulsivity and self-control. In this study, impulsivity was
assessed in humans using a computer task that measured delay and
probability discounting. Discounting describes how much the value
of a reward (or punisher) is decreased when its occurrence is
either delayed or uncertain. Twenty-four healthy adult volunteers
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 task the participants were given a
series of choices between a small, immediate, 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 the smaller immediate or certain reward and
the $10 delayed or probabilistic reward was identified using an
adjusting-amount procedure. The results indicated that (a) delay
and probability discounting were well described by a hyperbolic
function; (b) delay and probability discounting were positively
correlated within subjects; (c) delay and probability discounting
were moderately correlated with personality measures of
impulsivity; and (d) alcohol had no effect on discounting.
Key words: impulsivity, self-control, delay discounting,
probability discounting, alcohol, choice, humans