Examination of the effects of pimozide on two conditional discrimination problems differing in levels of task complexity

• 1.

  1. Two levels of task complexity were used to determine the degree to which pimozide, a DA receptor blocker, influenced performance on a conditional discrimination task.

• 2.

  2. Pigeons were trained on a simultaneous matching-to-sample task. On behalf the trials they were required to peck the side key that was the same color as the center key (identity matching). For the remaining trials subjects were presented with a symbolic matching procedure—red was correct when the sample was a vertical line and green was correct for a horizontal line. When performance was stable all subjects received four doses of pimozide i.m. (vehicle, 0.05, 0.15 and 0.45 mg/kg) according to a Latin Square sequence.

• 3.

  3. Pimozide increased response latencies and decreased rates of responding. Accuracy of responding on identity trials was not altered by pimozide while it was decreased on symbolic matching trials.

• 4.

  4. It was concluded that (a) highly complex tasks are more sensitive to the effects of pimozide than are simple tasks, and (b) dopaminergic systems may be involved in the maintenance of complex learned behavior.