The purpose of this study is to test the effects of a major dopaminergic drug of abuse, amphetamine, on time perception and time production under both short- and long-term treatment conditions in pigeons. Drug dependency is associated with increased impulsiveness. This impulsiveness has been linked to changed temporal discounting - drug abusers undervalue the future compared to the present and choose small immediate rewards in preference to larger delayed rewards to a greater degree than do non-abusers. The impulsiveness of habitual drug users may help to maintain their risky drug-taking behavior, as well as placing them in danger of disease and injury through other high-risk activities. One reason why drug users may undervalue future events is because of changes in their perception of time. Most drugs of abuse stimulate the dopamine neurotransmitter system and thus alter the perception and production of arbitrary time intervals. Consequently, drug abuse may have its observed effects on impulsivity by virtue of dopaminergic effects on time perception. Though prior studies have assessed the short-term effects of dopaminergic drugs on the timing of arbitrary intervals no prior attempts have been directed towards examining possible longer-term effects of dopaminergic drugs on time perception and production. Aside from their practical importance the results of these studies will also contribute to an ongoing debate about how dopamine controls timed behavior. Some theorists believe that drugs affect the speed of an 'internal clock.' We believe, however, that there is no internal clock as such, and that drugs influence the perception of time by altering the perceived salience of the events used to delineate time intervals in experiments on timing.
