A comparison of the effects of d-amphetamine, cocaine, imipramine and pentobarbital on local and overall rates of responding maintained under a four-component multiple fixed-interval schedule.

Key pecking of pigeons was maintained under a four-component multiple fixed-interval schedule with values of 1-min, 3-min, 5-min and 10-min. Each schedule value was correlated with a different key color, each of which controlled distinctively different performances. This schedule generated a range of response rates both within and across the different interval components that permitted a direct comparison of drug effects on local and overall rates of responding. d-Amphetamine, cocaine, imipramine and pentobarbital all increased low local response rates at doses that did not affect or decreased higher rates within each fixed interval. Similar effects were obtained when different overall rates of responding were analyzed except that imipramine and pentobarbital also increased the highest overall rates occurring under the 1-min schedule.