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An attempt was made to separate operant and elicited pecks occurring in multiple schedules of food reinforcement by moving the component stimuli to a second key, upon which pecks had no effect. The operant key stimulus was constant, regardless of the reinforcement schedule in effect. Experiments included two‐ and three‐component multiple schedules and a comparison of the single‐key and the two‐key procedures. In general, conditions that typically produce positive contrast in single‐key procedures reduced responding to the constant‐stimulus key (induction) and increased responding to the component‐stimulus key (contrast) in the two‐key procedure. The results were interpreted as supporting the contention that two response classes, operant and elicited, are present in standard multiple schedules. In addition, elicited responses were strongly implicated in contrast phenomena.

Differential reinforcement and imitation were used with two retarded children to train three sequential verbal responses associated with the display of a picture and questions related to that picture. Each response consisted of a three‐word chain in sentence form; combined with verbal responses from the experimenter, this trained sequence formed a short conversational unit. Three experimenters measured the use of each sentence in settings different than the one in which training took place, and with pictures different than those used during training. Two types of generalization sessions were used: (1) General sessions, during which 10 pictures never used during training were displayed to the subject with reinforcement delivered on a noncontingent basis, and (2) Intermixed sessions, during which 10 pictures never used during training were displayed to the subject, but a picture having received training was also displayed, and correct responses to this picture were reinforced on a variable schedule. Both subjects learned the sentences being trained. However, little generalization was evident from this training when all experimenters conducted General probe sessions. Generalization occurred with one experimenter only after that experimenter conducted Intermixed probe sessions. Generalization to a third experimenter was then observed (i.e., after the first two experimenters had conducted Intermixed probe sessions) without the use of Intermixed probe sessions by this third experimenter.

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To deal with the problem of stealing, an overcorrection procedure was designed in which the thief was required to give his victim an item identical to the stolen one in addition to returning the stolen item. This procedure was compared with the more commonly used simple correction procedure (restitution) in which the thief is required to return the stolen item. Under the simple correction procedure, an average of 20 thefts per day had been occurring among 34 retarded residents of an institution. The overcorrection procedure reduced the thefts by 50% on the first day, by 75% on the second day, and eliminated thefts by the fourth day, after which no further stealing occurred. The overcorrection procedure was a rapid and effective method of eliminating stealing, it provided special consideration for the victim, and it should be applicable to the nonretarded.

Food reinforcement for key pecking by three pigeons was arranged by a variable‐interval schedule and a device that assigned each reinforcement to one of 10 component response rates corresponding to 10 classes of equally reinforced interresponse times ranging from 1.0 to 6.0 sec in 0.5‐sec classes. The overall number of reinforcements per hour was varied from one to more than 60. Overall response rate was a monotonically increasing, negatively accelerated function of the overall number of reinforcements per hour. This function was decomposed into two time‐allocation functions: (1) the time allocated to all of the reinforced component response rates as a function of the total reinforcement rate, and, (2) the time allocated to a particular reinforced component response rate as a function of the reinforcement rate for that component. Asymptotic response rate was predicted by combining the asymptotes of the two separate time‐allocation functions: virtually all of the time was spent responding, and the percentage of the time spent responding that was allocated to a particular reinforced component response rate roughly equalled the relative reinforcements per hour for that component.

Pigeons received food only if they took longer than a specified time to begin and complete a fixed ratio. In Experiment 1, ratios with shorter durations had no stimulus consequence; in Experiment 2, these ratios ended with a stimulus change. In both studies, the mean time to complete the ratio exceeded requirements of less than 30 sec, approximately matched requirements of 30 sec, and fell progressively short of matching thereafter. Variability increased together with the means. The various effects resembled those of temporal differentiation experiments involving single responses. Although both number of ratios and time separating successive food presentations increased along with ratio duration, control experiments showed that differential reinforcement of duration, rather than either form or reinforcer intermittency, accounted for the performance. Experiment 2 also studied the effects of adding a stimulus that signalled when the required time had elapsed. The stimulus produced durations that matched even the most stringent requirements. This precision was not maintained when the stimulus was removed. Temporal differentiation schedules seem to have similar effects regardless of the response class and temporal property involved.

After learning to press keys in a predetermined serial position sequence, with timeouts scheduled as a consequence of errors, monkeys developed stereotyped errors. As soon as a new trial started, the animals would make an error. On trial after trial, they pressed the same incorrect key at the first member of the sequence, even though they had previously learned the sequence. First‐member errors occurred even when sequences of fully bright keys marking correct choices were presented. When timeout was eliminated as a consequence of one first‐member error, subjects switched to an error that did produce the timeout. When all first‐member errors failed to produce timeout the monkeys ceased responding. Both prefeeding and reduction in reinforcement density resulted in stereotyped errors occurring earlier in the session.

A variable‐interval schedule arranged food reinforcement for key pecking by pigeons on a single operandum at two rates, corresponding to two classes of reinforced interresponse times ranging from 1.5 to 2.5 sec and from 3.5 to 4.5 sec. The scheduled reinforcement rate for the higher component response rate was constant and equivalent to that of a variable‐interval 4‐min schedule. The scheduled reinforcement rate for the lower component response rate varied from zero to over 100 per hour. The number of occurrences of the constant component response rate varied inversely with the reinforcement rate for the variable component. This result, by definition a concurrent reinforcement interaction, or contrast, was the combined effect of two time‐allocation functions, which together determine mean response rate: the time allocated to both component rates as a function of the total reinforcement rate, and the time allocated to a particular component rate as a function of the percentage of reinforcements for that component. The present experiment reveals a further parallel between the controlling relations for free responding on a single operandum and those for choice between two operanda; in each case, a concurrent reinforcement interaction can be found that corresponds to matching.

Three rats were trained on an unsignalled shuttlebox‐avoidance task under three response‐shock intervals (10, 20, and 40 sec). Under all conditions, subjects developed excellent temporal gradients of avoidance; that is, response rate was an increasing function of time since last response. Although the response rate at any given interval of time after the previous response was inversely related to the response‐shock interval, there was an underlying similarity in the temporal gradients for the three intervals. In all cases, response rate relative to the maximum response rate was approximately equal to the proportion of the interval that had elapsed. This suggests that rats in unsignalled avoidance are estimating time from response completion, and that the units of the estimate are proportional parts of the response‐shock interval.

High‐speed photography of key pecking revealed that the arc described by the upper bill as a pigeon closes its beak is capable of operating a Lehigh Valley pigeon key set at 8 to 14 g. Arc‐produced switch closure follows initial switch closure in less than 50 msec. When birds were trained on ratio schedules, the probability of interresponse times (IRTs) shorter than 50 msec exceeded 0.30. Interval‐trained birds produced a much lower probability of short‐IRTs. When the schedules were reversed, there was only weak evidence of a reversal in the probability of short IRTs. A temporal analysis of topographic features observed in the original photographs failed to reveal differences between ratio and interval pecking topography. It appeared that only the point of contact with the key differed between subjects trained on the two schedules. It was concluded that only the locus, but not the topography, of the food‐reinforced key peck was modified by the schedule of reinforcement.