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In pigeons under fixed‐interval schedules of reinforcement, responding during most of the interval can be suppressed by stimulus conditions never present when a response is promptly followed by reinforcing stimuli. When the external stimuli obtaining immediately before reinforcement are presented during brief probe periods in the course of the interval, the rate of responding in the probe depends on the temporal position of the probe during the interval; the rate of responding is lower during a probe early in the interval than during one late in the interval. The present experiments show that the temporal dependency still holds (1) in birds with no experience under unmodified fixed‐interval schedules, (2) when the time between probes is spent in complete darkness, and (3) when food presentations are omitted at the end of 50% of intervals. The results strengthen and extend the conclusion from previous studies that the time relations themselves are the primary control of rate of responding under fixed‐interval schedules of reinforcement.

Pigeons were studied under FI 500 sec in which an SΔ was present throughout the interval except during the terminal 50‐sec segment and one earlier 50‐sec segment. Very little responding occurred during the presence of SΔ. The rate of responding in the earlier 50‐sec SD segments was lower than in the terminal SD segment. There was a clear trend for the rate of responding in the earlier SD segment to be progressively higher the later it occurred in the course of the FI 500 sec. This trend was shown roughly to parallel the increasing rate of responding in a conventional FI 500 sec with no interruption by SΔ. Since the changing tendency to respond through the FI survives massive disruption by SΔ, it is concluded that the control of responding through the FI does not require continuous mediating behavior. It is suggested that it is the decaying retroactive influence of the reinforcer on responses that occurred longer and longer before the reinforcer occurred which produces the familiar scalloped pattern of responding under FI schedules.

In each of two experiments human subjects were intermittently reinforced with money on a fixed‐ratio schedule for emitting correct matching responses. A pre‐time‐out stimulus which signaled removal of positive reinforcement was periodically superimposed. In the first experiment the superimposed pre‐time‐out stimulus was paired with a 1‐min or 4‐min response‐independent time out. In the second experiment the pre‐time‐out stimulus was paired with a 1‐min or 4‐min time out contingent on the incorrect responses. The pre‐time‐out stimulus did not markedly influence performance when the time out was response independent. In contrast, the pre‐time‐out stimulus markedly suppressed incorrect responding when the time out was contingent on the incorrect responses. When duration of this time‐out was increased from 1‐min to 4‐min, suppression of incorrect responding increased and correct responding was suppressed. Therefore, behavioral suppression by a pre‐time‐out stimulus was obtained only when the signaled aversive event—time out—was response produced. In this case, suppression was influenced by time‐out duration.

Three experiments sought to evaluate the effect of electroconvulsive shock on the action of a reinforcing stimulus. In all experiments behavior was maintained on a 2 min variable interval schedule for food reinforcement. Foot shock at the termination of a buzzer stimulus served as the reinforcing stimulus for conditioned suppression during the ensuing buzzer interval. Omission of foot shock at the termination of the buzzer stimulus was followed by normal responding (no conditioned suppression) during the next buzzer interval. In Exp I electroconvulsive shock followed foot shock at varying time intervals. In the first subsidiary experiment electroconvulsive shock followed an unreinforced buzzer stimulus at varying time intervals. In the second subsidiary experiment electroconvulsive shock followed foot shock at varying time intervals and an additional buzzer stimulus was sounded between the termination of foot shock and the onset of electroconvulsive shock. These three experiments demonstrated that electroconvulsive shock invariably abolished the effects of the reinforcing stimulus if it followed conditioning by no more than 10.0 sec and never had an effect if it followed conditioning by 12.5 sec or more; electroconvulsive shock was not acting as a reinforcing stimulus in this situation.

Schedule‐induced polydipsia occurred during initial magazine training to Noyes pellets (45 mg), disappeared when lever‐pressing was acquired on a continuous reinforcement schedule (CRF), and reappeared when the food contingency was changed to a 1‐min variable interval schedule (VI 1 min). Polydipsia also developed under a VI 1 min food schedule when water was concurrently available on various fixed ratios (FR), rather than being freely available. The level of the polydipsia and its motivating properties allow it to be classified as a form of adjunctive behavior.

Measurements of the post‐reinforcement pause and response rate were obtained from four birds on a range of fixed ratio schedules from 25 to 150. The results indicated a consistent increase in the length of the pause as the ratio was increased. Response rate tended to decrease, but these data were less consistent and some reversals were apparent.

A new schedule of reinforcement was used to maintain key‐pecking by pigeons. The schedule reinforced only pecks terminating interresponse times which occurred least often relative to the exponential distribution of interresponse times to be expected from an ideal random generator. Two schedule parameters were varied: (1) the rate constant of the controlling exponential distribution and (2) the probability that a response would be reinforced, given that it met the interresponse‐time contingency. Response rate changed quickly and markedly with changes in the rate constant; it changed only slightly with a fourfold change in the reinforcement probability. The schedule produced stable rates and high intra‐ and inter‐subject reliability, yet interresponse time distributions were approximately exponential. Such local interresponse time variability in the context of good overall control suggests that the schedule may be used to generate stable, predictable, yet sensitive baseline rates. Implications for the measurement of rate are discussed.

Pigeons were trained to respond equally to various orientations of three parallel lines projected on a response key. One group was then punished for responding to the vertical lines, but not punished in a line‐absent condition. Two other groups were also punished but had no opportunity to make such a discrimination. Orderly generalization gradients were obtained from the discrimination group during recovery from punishment, with least responding to the vertical lines and higher rates to other orientations. Gradients obtained from the non‐discrimination groups were flat. A discrimination of punishment contingencies appears to be necessary for a stimulus correlated with punishment to acquire control over its reductive effects.

Twenty‐six rats were used to study the development of stable conditioned responding to terminate white noise (100 or 105 db) in a tilt cage apparatus. Preliminary work, with one end of the cage consistently associated with silence, demonstrated stability at a high level of cumulative noise‐off time per session. Time spent at the noise‐off cage end was unaffected by lay‐off and showed adaptation to reversal of the cage end functions. Variability in reversal acquisition, insensitivity to stimulus intensity changes and persistence in remaining at one end of the cage in the absence of noise‐termination contingencies indicated the need for more precise behavioral control. A schedule programming several reversals of the no‐noise end at variable intervals within each session was developed. Performance on the latter schedule was characterized by stability of high noise‐off times and also proved more sensitive than the preliminary method to stimulus intensity changes (55, 70, 100 db) as measured by both cumulated noise‐off time and cage crossing rates. The ease of training combined with sensitivity to stimulus change and the lack of highly specific motor response requirements make this technique promising for use with animals potentially debilitated by drugs or surgical aftereffects.

A free operant procedure was used to determine whether or not one rat could discriminate: (1) between the presence and absence of a second rat, and (2) between two other rats of the same species and sex. The subjects were four male Wistar rats. The discriminatory response was a bar press and food was used as reinforcement during training. Although there were wide individual differences in rate of learning, all subjects learned to make both discriminations.