The effects of phenobarbital on responding under delayed-matching-to-sample procedures with differential and nondifferential outcomes.

Pigeons were exposed to delayed-matching-to-sample procedures in which food or a flash of the feeder light followed correct responses. When these consequences were correlated with a particular stimulus (e.g., food followed matching responses to red and a flash of the feeder light followed matching responses to green), accuracy was significantly higher (i.e., stimulus control was greater) than when discriminative stimuli and consequences were not correlated. Acute administrations of phenobarbital (10-40 mg/kg) produced similar effects regardless of whether or not differential outcomes were arranged for correct responses to a particular stimulus. At doses of 30 and 40 mg/kg, phenobarbital significantly decreased accuracy under both variations of the delayed-matching-to-sample procedure. Given these results, it appears that degree of stimulus control in the absence of drug did not modulate drug effects in the present study.