Drug discrimination training with a single choice trial per session.

All drug discrimination procedures share in common the practice of providing for multiple choice opportunities per training session. This practice allows nondrug cues (presence or absence of reinforcement) to mediate choice behavior during that portion of the session following the initial choice. Investigators who have acknowledged this problem typically use only first-trial choice performance to evaluate discriminative control by the drug cue, and consider additional choice training following the delivery or nondelivery of the first reinforcer to be facilitatory in establishing drug-mediated discriminative control. In this experiment, rats were trained to discriminate 4.0 mg/kg morphine from saline in a novel procedure that employed a single choice trial per training session. Choice performance was characterized during discrimination acquisition and in subsequent stimulus generalization testing. The results indicated that when all reinforcers are made contingent on correct performance during a single choice trial, rapid and stable control of drug-mediated choice behavior, is observed. In addition, the results demonstrated that additional choice training following the delivery or nondelivery of the first reinforcer is not a necessary antecedent toward establishing drug-mediated discriminative control.