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Pigeons' responses in the presence of two concurrently available (initial‐link) stimuli produced one of two different (terminal‐link) stimuli according to identical but independent variable‐interval schedules. Responding in the mutually exclusive terminal links was reinforced with food according to fixed‐ratio schedules for six pigeons and according to fixed‐interval schedules for two pigeons. None of the pigeons matched the proportion of (choice) responses in the initial links to the proportion of the rates of reinforcement obtained during the terminal links. Instead, as the values of each of the terminal‐link schedules were increased by a constant amount, the choice proportions for the stimulus associated with the smaller of the two values increased, even though the relative rates of reinforcement during the terminal links decreased. These results are incompatible with those from previous studies with aperiodic (variable‐interval or variable‐ratio) schedules. The present results do suggest, however, that in transforming aperiodic schedules into their periodic equivalents, it may be necessary to consider the size of the smallest interreinforcement interval comprising the terminal‐link schedules.

Pigeons distribute their responses on concurrently available variable‐interval schedules in the same proportion as reinforcements are distributed on the two schedules only when a changeover delay is used. The present study shows that this equality between proportions of responses and proportions of reinforcements (“matching”) is obtained when the value of the changeover delay is varied. When responses are partitioned into the set of rapid response bursts occurring during the delay interval and the set of responses occurring subsequently, the proportion of neither set of responses matches the proportion of reinforcements. Instead, each set deviates from matching but in opposite directions. Matching on the gross level results from the interaction of two patterns evident in the local response rates: (I) the lengthening of the changeover delay response burst is accompanied by a commensurate decrease in the number of changeovers; (2) the changeover delay response burst is longer than the scheduled delay duration. When delay responses are eliminated by introducing a blackout during the delay interval, response matching is eliminated; the pigeon, however, continues to match the proportion of time spent responding on a key to the proportion of reinforcements obtained on that key.

Self‐determined, experimenter‐determined, and chance‐determined token reinforcement treatments were compared with a no‐token treatment, in terms of effect on the learning of history and geography material in the classroom. Each treatment was assigned to one of four heterogeneous classes of Grade nine girls. An initial baseline period preceded the differential reinforcement period, and a token withdrawal period followed. Subsequently, the self‐determined treatment was employed in all three token reinforcement classes, before a final baseline period occurred. Findings included a similarity of initial baseline performance for all classes, an equal superiority of self‐determined and experimenter‐determined treatments to chance‐determined and no‐token treatments, and significant improvement from initial baseline to final baseline for self‐determined and experimenter‐determined treatments, but not chance‐determined and no‐token treatments. Differential token reinforcement experience was found to influence subsequent rate of self‐determined token reinforcement.

Every tenth lever‐press of three morphine‐dependent rhesus monkeys was reinforced with food. A red light, initially a neutral stimulus, was presented every third or fourth session for 5 min before and 5 min after an intravenous injection of nalorphine, a morphine antagonist that produces an immediate abstinence syndrome in morphine‐dependent monkeys. After several pairings, conditioned suppression of lever pressing, heart‐rate decrease, vomiting, and excessive salivation were observed during the red‐light period before nalorphine injection. No conditioned electrocardiogram, respiration or temperature changes occurred. After 10 red light‐nalorphine pairings, morphine administration was completely discontinued and monkeys were then tested monthly for persistence of the conditioned responses. The red light paired with saline injection continued to suppress lever pressing and to produce heart‐rate decreases after 60 to 120 days of complete abstinence from morphine. Subsequently, daily presentations of the red light‐saline injection complex rapidly extinguished these conditioned responses. Nevertheless, they could be rapidly reinstated by additional nalorphine injections.

Pigeons were trained in a three‐key chamber to peck one side key in the presence of a vertical line on the center key and to peck the other side key in the presence of a horizontal line. Correct choice responses were reinforced with food according to fixed‐ and variable‐ratio, fixed‐interval, and differential‐reinforcement‐of‐long‐latency schedules of reinforcement. For each schedule, the birds performed under each of two conditions: (1) each correct choice response produced a brief presentation of stimuli intermittently paired with food, then the next trial; (2) each correct choice response produced an intertrial interval only. For all schedules except one long latency schedule, response rates were higher under the condition of brief stimulus presentation than under the comparable control condition. Presentation of brief magazine stimuli increased choice accuracy. The amount of change in accuracy was correlated with the rate of food presentation. Performance under the schedules with highest food reinforcement rates showed no enhancement; performance under the schedules with the lowest reinforcement rates showed the greatest enhancement.

Previous experiments have shown that positively reinforced operant responding is suppressed during a conditioned stimulus terminated with an electric shock (conditioned suppression). In the present experiment, the conditioned stimulus was terminated with a positive unconditioned stimulus, and it was found that the duration of the conditioned stimulus was a key factor in determining whether response suppression or response enhancement was observed during the stimulus. The lever‐pressing responses of rats were maintained by a variable‐interval schedule of food reinforcement. While the rats were pressing the lever, a light was occasionally turned on, its offset coincident with a brief period of access to a sucrose solution. In consecutive blocks of sessions, the light duration was 40 sec, 12 sec, or 120 sec. Results showed that the rate of lever pressing was substantially suppressed during the 12‐sec stimulus, slightly suppressed during the 40‐sec stimulus, and enhanced during the 120‐sec stimulus.