Three adolescent marmosets were trained on simultaneous and successive versions of a red-white visual discrimination task. The effects of doses of 0.2-1.2 mg/kg D-amphetamine on the performance of these tasks were assessed using a balanced design. It was found that while there was no drug effect on performance of the simultaneous task, amphetamine exerted a dose dependent disruptive effect on the successive version of the task. It is argued that amphetamine disrupts response control rather than discriminative ability and, in this respect, resembles the effect of orbitofrontal and limbic lesions in contrast to other neocortical lesions.
