The present study examined the acquisition of lever pressing in rats under three procedures in which food delivery was delayed by 4, 8, and 16 seconds relative to the response. Under the nonresetting delay procedure, food followed the response selected for reinforcement after a specified interval elapsed; responses during this interval had no programmed effect. Under the resetting procedure, the response selected for reinforcement initiated an interval to food delivery that was reset by each subsequent response. Under the stacked delay procedure, every response programmed delivery of food t seconds after its occurrence. Two control groups were studied, one that received food immediately after each lever press and another that never received food. With the exception of the group that did not receive food, responding was established with every procedure at every delay value without autoshaping or shaping. Although responding was established under the resetting delay procedure, response rates were generally not as high as under the other two procedures. These findings support the results of other recent investigations in demonstrating that a response not previously reinforced can be brought to strength by delayed reinforcement in the absence of explicit training.

The effects of the antiepilepsy drugs methsuximide and mephenytoin were examined in pigeons responding under a fixed-consecutive-number (FCN) schedule with and without an added external discriminative stimulus. On this schedule, food was delivered whenever subjects responded between 8 and 12 times on one response key (work key), and then responded once on a second response key (reinforcement key). Under one variant of the FCN schedule (FCN 8-SD), an external discriminative stimulus signalled completion of the response requirement on the work key; no such stimulus change occurred under the other (FCN 8) schedule. The two FCN schedules (with an without stimulus change) alternated at 5-min intervals within each session for all subjects. Methsuximide (25-200 mg/kg) and mephenytoin (40-160 mg/kg) produced generally dose-dependent decreases in percentage of reinforced response runs and rate of responding. The magnitudes of these effects were comparable under both variants of the FCN schedule.