Rats can learn simultaneous four‐drug discriminations in four‐lever boxes

Rats were required to learn a four‐drug discrimination in compartments containing four levers. The training drugs were phenobarbital 35 mg/kg, nicotine 0.8 mg/kg, fentanyl 0.04 mg/kg, and methylphenidate 5 mg/kg. Responding on a different lever was reinforced with 0.1 ml sweetened water under each drug condition. The experiment tested whether such four‐drug discriminations could be learned, and whether the rate of acquisition and/or asymptotic accuracy of the discriminations would be increased in boxes where each lever was surrounded by a unique sensory environment created by special materials on the floors, walls, and ceiling in the vicinity of the lever (e.g., plastics, wire screens). Four different training compartments were employed. The required discriminations were learned by most rats. The use of unique decorations around each lever decreased the mean number of sessions before the appearance of discriminative control from 90 to 67. It also made asymptotic accuracy significantly higher in some sensory environments than in others. suggesting that animals “preferred” some environments. The training drugs were apparently not equally discriminable at the doses employed, as both sessions to criterion and asymptotic accuracy differed for the various drugs employed.