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Two dogs were maintained on a multiple schedule having both a food reinforced and an avoidance component (Mult VI 1′ SΔ AvoidSS20 RS20 SΔ). The effects of superimposing an Estes‐Skinner procedure for delivering unavoidable shocks on all components of the multiple schedule were observed. The buzzer‐shock pairing of the Estes‐Skinner procedure produced an increased rate of responding on the avoidance component of the schedule and also on the SΔ components. No persistent change in rate was observed on the food component during the pre‐shock stimulus. Control performances on all components could be regained by either extinguishing or eliminating the buzzer‐shock pairing. Extinction of the avoidance responding had little effect on the increased rates of responding produced by the Estes‐Skinner procedure on the SΔ and avoidance extinction components and did not lead to a conditioned suppression of the food reinforced responding. Rate of responding during the pre‐shock stimulus was observed to be relatively independent of changes in the maintaining schedules. Responding during the pre‐shock stimulus could be conditioned and maintained after an extensive history of avoidance extinction.

The utterances of particular words—“selected verbal responses” (SVR's)—were reinforced according to five different drl schedules and studied under changes in the schedule and/or the SVR. The emissions of SVR's were shaped by the procedure, while the rates of saying all the different words were unaffected. The distributions of the percentages of different IRT's and IRT's/OP's changed very little when only the SVR was changed, suggesting that reinforcements had their main effect upon some kind of “delaying behavior.” The modal IRT classes were just above the drl specifications, and there was no evidence of a second modal class at short IRT's. The differences between actual and optimum median IRT's were fairly constant under different drl schedules. Individual differences appeared in the behavior interpolated between SVR's: some subjects (Ss) counted the number of intervening words, some reported increases in tension, and still others seemed to change the pitch of voice in a cyclical pattern. The transcripts of intervening verbal behavior indicated the presence of some chains of words, presumably formed before the experiment and “adapted” to the length of the delay required for reinforcement. In the experimental situation the formation of verbal chains was only rarely observable.

Animals learn to avoid with the Sidman procedure even though the avoidance response is not followed by the termination of any warning stimulus in the environment. What reinforces this response? The accepted explanation has been that the avoidance response is reinforced when it terminates other behavior that has become aversive by pairing with shock. However, the reinforcement may also be derived from the temporal discriminations that develop with Sidman avoidance. These and other temporal discriminations show that the animal has available some events that vary with the postresponse time. The shock will closely follow the temporal stimuli at long postresponse times and would be expected to make them aversive. The stimuli at short postresponse times would have a relatively low aversiveness due to their more remote relation to shock. Since the avoidance response changes a long postresponse time to a short one, that response would be followed by a decrease in aversiveness which would reinforce it. When sharp temporal discriminations are present, reinforcement from the decrease in aversiveness of temporal stimuli probably plays a dominant role in maintaining the avoidance response. This formulation fits the available data and has adequate answers for the objections that have been raised to earlier conceptions of the role temporal discriminations might play in Sidman avoidance. Although under some conditions the reinforcement in Sidman avoidance seems to be primarily due to the decrease in aversiveness of temporal stimuli, under other conditions there probably is reinforcement from the termination of conditioned aversive responses.

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Only one of two keys reinforces the subject with food. This key can assume one of two colors, each associated with a different fixed‐ratio schedule for obtaining reinforcement. The function of the second key is to permit the animal to switch from the long schedule to the short schedule. If the difference between the ratio schedules is large enough, a preference for the shorter schedule is demonstrable. A quantitative index of preference is obtained as follows: each time the animal switches to the shorter schedule, the number of pecks required to produce the next switch is increased. As the “ante” on the switching key increases, the effective difference between the two ratio schedules decreases. After each food reinforcement, when the bird is exposed to the choice‐situation, it takes longer before the bird switches again. This is used to “titrate” the bird's preference. If it does not switch within x sec, the progressively increasing ratio schedule of the switching key is decreased. A specific value, in terms of a rather specific number of responses the bird settles at on the choice key, is obtained. This equilibrium is employed as a dependent variable. Several variables of which it is a function are explored.

Previous results suggest that a stimulus paired in Pavlovian fashion with reward should exert some discriminative control over an unrelated operant response acquired under a different drive‐reward system. In the following experiment, a stimulus was first paired with food reinforcement for a hungry rat. Subsequently, the animal learned to lever‐press for water reinforcements when thirsty but not hungry. Finally, the control over lever‐pressing of the food‐paired stimulus was tested by presenting it at various times during extinction of the lever‐pressing response. All animals in the experiment showed the expected effect; each emitted more lever‐presses during periods of the food‐paired stimulus than during alternate control periods.

Temporal schedules of negative reinforcement were derived in a manner analogous to those for positive reinforcement, and two parametric studies were carried out with two of the three defining variables. With some limiting values of the defining variables, escape schedules result and data obtained at these values were similar to those obtained in escape studies. At other values of the defining variables avoidance behavior was generated.

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