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Sequential dependencies were investigated with two rats in a mixed and in a tandem differential‐reinforcement‐of‐low‐rate‐responding schedule. In each schedule, 5‐sec and 15‐sec components were presented in fixed alternation. In the mixed schedule, a 5‐sec interresponse time followed a 15‐sec interresponse time and a 15‐sec interresponse time followed a 5‐sec interresponse time in predictable sequence. The correlation between prior and subsequent interresponse times, however, existed only when the prior interresponse time resulted in reinforcement. In the tandem schedule, an interresponse time greater than 5 sec in the differential‐reinforcement‐of‐low‐rate 5‐sec component was not associated directly with reinforcement. One subject demonstrated sequential response patterns similar to those noted in the mixed schedule, even though the prior 5‐sec interresponse time was not reinforced in the tandem schedule. The results indicate that the prior interresponse time length alone is not sufficient to influence the subsequent interresponse time length. Implications are, however, that a temporal response pattern arises when an interresponse interacts with schedule contingencies to control the interreinforcement interval.

Instructions, discrimination procedures, and sources of reinforcement were manipulated in order to determine the bases for the maintained “non‐reinforced” imitations observed in generalized imitation research. Six girls received imitation training from two exprimenters, One experimenter modelled only reinforced responses; the other modelled only non‐reinforced responses. The children imitated all responses when no reinforced alternative was available, even though results of choice procedures and special instructions clearly demonstrated that they discriminated reinforced from non‐reinforced responses. Instructions not to perform non‐reinforced imitations immediately eliminated these behaviors. It is suggested that social setting events may be largely responsible for generalized imitation.

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The present experiment sought to develop a practical and effective method for teaching the beginning elements of hand‐writing in a Head Start program. The method consisted of reinforcing responses to a writing program by giving the children access to a variety of activities normally available in the pre‐school classroom. Tokens were presented for correct responses. The children then used the tokens to select reinforcers, such as snacks and access to a variety of play activities. In an experimental evaluation of the token system, it was found that responding was maintained as long as access to the reinforcing activities was contingent upon responding. When reinforcement was no longer contingent upon responding, virtually no responding occurred. Informal observations suggested that the token system had several unanticipated effects: the children's vocabulary and ability to understand instructions improved; a favorable attitude toward school developed; and their ability to play cooperatively with other children increased. It was concluded that the token system is a practical and effective method for teaching beginning writing skills and that it has other desirable, if unanticipated, effects.

Two experiments investigated how the addition of time limits affected fixed‐ratio behavior. In Exp. 1, pigeons obtained food only if they completed the ratio within a specified time after the end of the preceding ratio. In Exp. 2, they obtained food only if they took longer than a specified time. Failures to meet the time criteria produced brief timeouts. The times taken depended on the requirements in both experiments. In Exp. 1, progressively briefer time criteria resulted in faster ratios, and in Exp. 2, longer time criteria increased the time taken in each ratio. The pigeon's sensitivity to the temporal variable, a property of the entire period extending from the first opportunity to respond to the end of the ratio, indicated that performance involved a behavioral unit encompassing both the post‐reinforcement pause and the responses comprising the ratio.

A procedure (“discrete‐trial” avoidance) was devised to differentiate between the two main theories of responding in Sidman's “free‐operant” avoidance procedure. One theory, a version of two‐factor theory, holds that responding is reinforced by the removal of a conditioned aversive stimulus. The conditioned aversive stimulus is held to be temporal, which accounts for the spaced responding, or timing, that Sidman's procedure produces. The other theory holds that the reinforcement for both responding and timing is shock‐frequency reduction. The new procedure eliminated this reinforcement for timing, but retained the conditions for the formation of conditioned aversive temporal stimuli. According to one theory, the new procedure should have sustained timing as well as Sidman's, while according to the other, it should have sustained no timing. The results confirmed neither theory. Timing was found with both procedures, but unequally in degree and kind. Large variations in the precision of timing did not appear to be correlated with successful avoidance for either procedure.

In a restraining device, providing a constant localization and easy placement of stimulating electrodes, rats were conditioned to push a front panel in order to reduce the intensity of a shock which otherwise increased regularly every 10 sec. Rapid conditioning was obtained from all subjects. They showed a very stable behavior, with negligible inter‐ or intra‐individual variability throughout very long experimental sessions. The operant nature of the response was demonstrated further in extinction, where no shock was delivered, and in situations where the animal could not change the predetermined intensity of the shock. The interpretation of the obtained threshold was discussed with reference to previous studies on titration schedule. It was suggested that, with the parameters used, the shock intensity at which it was maintained by the rats' behavior, had the value of a warning signal, and that, in this particular case, the titration schedule generated mainly discriminative avoidance behavior rather than escape behavior.

Three retarded children were trained, using imitation and reinforcement procedures, to produce past and present tense forms of verbs in response to verbal requests. Two types of experimental sessions were arranged: training sessions and probe sessions. During training sessions, a child was trained to produce one verb in both the past and the present tense. Then, in a probe session, the generalization of this training was tested by presenting to the child a series of untrained verbs interspersed with previously trained verbs. Responses to untrained verbs were never reinforced. Training sessions alternated with probe sessions throughout a multiple baseline design involving four classes of verb inflections as the baselines. The results showed that, as past and present tense forms of verbs within an inflectional class were trained, the children correctly produced past and present tense forms of untrained verbs within this class. When verbs from two or more classes were trained, the children correctly produced the verb tenses from each of these classes. Thus, the imitation and reinforcement procedures were effective in teaching generative use of verb inflections.

Two‐key concurrent responding was maintained for three pigeons by a single variable‐interval 1‐minute schedule of reinforcement in conjunction with a random number generator that assigned feeder operations between keys with equal probability. The duration of blackouts was varied between keys when each response initiated a blackout, and grain arranged by the variable‐interval schedule was automatically presented after a blackout (Exp. I). In Exp. II every key peck, except for those that produced grain, initiated a blackout, and grain was dependent upon a response following a blackout. For each pigeon in Exp. I and for one pigeon in Exp. II, the relative frequency of responding on a key approximated, i.e., matched, the relative reciprocal of the duration of the blackout interval on that key. In a third experiment, blackouts scheduled on a variable‐interval were of equal duration on the two keys. For one key, grain automatically followed each blackout; for the other key, grain was dependent upon a response and never followed a blackout. The relative frequency of responding on the former key, i.e., the delay key, better approximated the negative exponential function obtained by Chung (1965) than the matching function predicted by Chung and Herrnstein (1967).

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