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Two‐key conjunctive schedules were studied with one key (food key) under a differential‐reinforcement‐of‐low‐rate 20‐sec schedule, while the consequences of responding on another key (collateral key) were varied. When food depended not only upon a food‐key interresponse time in excess of 20 sec, but also upon the occurrence of one or more collateral‐key responses during the food‐key interresponse time, the rate of collateral‐key responding was low and food‐key interresponse times rarely exceeded 20 sec. When collateral‐key responses could produce a discriminative stimulus correlated with the availability of food under the DRL schedule, the discriminative stimulus functioned as a conditioned reinforcer to maintain higher rates of collateral‐key responding, and the spacing of food‐key responses increased. If the occurrence of the discriminative stimulus was independent of collateral‐key responses, the rate of collateral‐key responding was again low, but the spacing of food‐key responses was still controlled by the discriminative stimulus. Both the conditioned reinforcer and the explicit reinforcement contingency could maintain collateral‐key responding, but the adventitious correlation between collateral‐key responses and the delivery of food could not maintain very much collateral‐key responding. The pattern of responding on the food‐key was determined to a much greater extent by the correlation between the discriminative stimulus and the delivery of food than by the pattern of responding on the collateral key.

Pigeons were trained to key‐peck for food, first with single‐stimulus training and then with successive discrimination (multiple schedule) training. In the multiple schedule, two different wavelengths were each correlated with equally frequent variable‐interval reinforcement but different durations (6 sec vs. 2 sec) of access to grain. For some birds, the different durations of feeding cycle were cued by different intensities of the food hopper light. For some of these “cued” birds, single‐stimulus training had been carried out with 6‐sec feedings and when multiple‐schedule training was introduced, the novel stimulus was correlated with 2‐sec feedings. For the others, 2‐sec feedings were originally used, and the novel stimulus was then present during the 6‐sec reinforcement duration. The cueing procedure enhanced discrimination performance, and was necessary for the consistent production of a peak shift. In addition, the condition in which original training had been carried out with 6‐sec feedings, and thus reinforcement duration was reduced in the presence of the novel stimulus, led to the best performance.

Two variables often confounded in fixed‐ratio schedules are reinforcement frequency and response requirement. These variables were isolated by a technique that yoked the distributions of reinforcements in time for one group of pigeons to those of pigeons responding on various fixed‐ratio schedules. The contingencies for the yoked birds were then manipulated by adding various tandem fixed‐ratio requirements to their schedules. Post‐reinforcement pause was approximately equal for the yoked and ratio pigeons, and was relatively insensitive to changes in the tandem requirement. Terminal response rate increased with increases in the tandem requirement, even though reinforcement rate was invariant. This increase was attributed to the progressive interference of the tandem requirement with the differential reinforcement of long interresponse times.

Human macrosaccadic eye movements to two areas of a four‐dial display were conditioned by concurrent variable‐interval schedules of signals. Reinforcers (signals) were delivered to the two right‐hand dials on one schedule and to the two left‐hand dials on another, independent schedule. The use of a changeover delay between crossover eye movements and reinforcement had the effect of changing the pattern of scanning from fixating four dials in succession or in a Z‐shaped pattern to scanning vertically the dials on either side with fewer crossovers. In the presence of a changeover delay, subjects matched relative eye‐movement rates and relative reinforcement rates on each schedule. Rate of crossover eye movements, with a changeover delay in effect, was also inversely related to the difference in reinforcements arranged by the concurrent schedules. The results suggest that for stimuli whose critical components are arranged spatially, conditioned eye movements play an important part in selective stimulus control.

Experiments with pigeons and rats showed that: (1) When a brief blackout was presented in lieu of reinforcement at the end of 25% of intervals on a fixed‐interval 2‐min schedule, response rate was reliably and persistently higher during the following 2‐min intervals (omission effect). This effect was largely due to a decrease in time to first response after reinforcement omission. (2) When blackout duration was varied, within sessions, over the range 2 to 32 sec, time to first response was inversely related to the duration of the preceding blackout, for pigeons, and for rats during the first few sessions after the transition from FI 2‐min to FI 2‐min with reinforcement omission. Post‐blackout pause was independent of blackout duration for rats at asymptote. These results were interpreted in terms of differential depressive effects of reinforcement and blackout on subsequent responding.

The effectiveness of television distortion as a negative reinforcer was analyzed. Contingency arrangements involving television distortion were found to be capable of (a) accelerating the work rate of a naive, mildly retarded subject on a simulated production‐line task involving card‐sorting, and (b) reducing gross hyperactivity of a mildly retarded subject. An escape‐avoidance contingency was arranged for the production‐line behavior of the first subject and a punishment contingency for the hyperactive behavior of the second subject. Television distortion appears to be an effective and practical negative reinforcer for use in behavior modification.