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The relative lengths of two concurrently reinforced interresponse times were varied in an experiment in which three pigeons obtained food by pecking on a single key. Visual discriminative stimuli accompanied the two time intervals in which reinforcements were scheduled according to a one‐minute variable‐interval. The steady‐state relative frequency of an interresponse time approximately equalled the complement of its relative length, that is, its relative harmonic length. Thus, lengths of interresponse times and delays of reinforcement have the same effect on the relative frequencies of interresponse times and choices in one‐key and two‐key concurrent variable‐interval schedules, respectively. A second experiment generalized further the functional equivalence between the effects of these one‐key and two‐key concurrent schedules by revealing that the usual matching‐to‐relative‐immediacy in two‐key concurrent schedules is undisturbed if reinforcement depends upon the occurrence of a response at the end of the delay interval, as it does in the one‐key schedules. The results of both experiments are consistent with a quantitative theory of concurrent operant behavior.

Imprinted ducklings were trained to peck a pole using brief presentations of the imprinted stimulus as the response‐contingent (reinforcing) event. Subjects' were then permitted to spend extended periods with continuous access to food and the imprinted stimulus (via a pole peck). For other (control) subjects the experimental situation was restricted to either responding for the stimulus, or feeding in the absence of the stimulus. For subjects in the control conditions, both activities occurred in cyclic fashion. When, however, there was continuous opportunity to respond for the stimulus and food was available, the tendency to respond was related to the tendency to feed. Other experiments showed that independent presentations of the stimulus could initiate feeding in imprinted ducklings with no prior pairing of the stimulus with food and with no prior pole‐peck training. The most consistent control over feeding, however, was exhibited by ducklings that were imprinted and also accustomed to periodic removals of the stimulus. It is concluded that in ducklings, imprinting procedures are sufficient to endow an arbitrary stimulus with the capacity to release feeding behavior.

Two rough‐toothed porpoises (Steno bredanensis) were individually trained to emit novel responses, which were not developed by shaping and which were not previously known to occur in the species, by reinforcing a different response to the same set of stimuli in each of a series of training sessions. A technique was developed for transcribing a complex series of behaviors on to a single cumulative record so that the training sessions of the second animal could be fully recorded. Cumulative records are presented for a session in which the criterion that only novel behaviors would be reinforced was abruptly met with four new types of responses, and for typical preceding and subsequent sessions. Some analogous techniques in the training of pigeons, horses, and humans are discussed.

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The present experiments demonstrated a reliable within‐session increase in rectal temperature (Tre) at 25° C during stable differential‐reinforcement‐of‐low‐rate (DRL) performance. The thermal response was found to be independent of the DRL value and reinforced DRL performance, but dependent on the state of the animal's deprivation. Exposure to a 35°‐C environment increased the post‐session Tre significantly above the 25°‐C post‐session Tre for seven of eight subjects. Response and reinforcement rate at 35° C was found to be independent of DRL value, although it decreased as DRL value increased at 25° C. A discriminative stimulus used to mark the end of the interval increased the reinforcement rate at 25° C but provided no advantage at 35° C. Measurement of the pattern of responding during DRL performance revealed increases in the proportion of long interresponse times at 35° C. Reinforcement rate was found to decrease progressively at 35° C, reaching a minimum within 40 to 50 min of the 90‐min session. Visual observation of overt behaviors during DRL performance at 35° C revealed a reduction in the frequency of overt behavior, characteristic of 25°‐C performance, and a time‐dependent increase in the probability of an alternative set of behaviors.

Pigeons emitted interresponse times that were reinforced if they fell between an upper and a lower bound (t < IRT < t + t/10). Brief stimuli followed each response; under some experimental conditions the color of these stimuli was correlated with whether the preceding interresponse time was longer or shorter than that specified by the schedule. Preliminary experiments indicated that these “feedback” stimuli acquired no discriminative properties even after prolonged training. A modified procedure, in which t varied cyclically throughout each experimental session, allowed the stimuli to acquire such properties: stimulus control was demonstrated under the training conditions, for two of the pigeons, and under transfer conditions for all three birds. A series of probe conditions, followed by a replication of the simple procedure using a multiple schedule, indicated that the controlling property of the stimuli was not the relation between stimuli, interresponse time, and value of t, but a variable determined by the interaction between the animals' responding and the cyclic procedure. This variable was probably the relative frequency of the less‐frequent feedback stimulus.

Two hooded rats were trained to bar‐press to avoid electric shock on a continuous avoidance schedule with response‐shock and shock‐shock intervals equal. The rate of delivery of response‐independent shocks superimposed on this schedule was varied. The response‐independent shocks led to generally higher response rates but, with responses during shock omitted, the rates decreased as the response‐independent shock rate was increased. The actual shock rate received by the subjects was linearly related to the maximum potential shock rate. There was an increasing, negatively accelerated function between percentage avoidance and response rate, but there was no consistent relation between the number of shocks avoided and response rate. Response rate decreased as the potential shock rate increased, but responding was maintained even when as few as 15% of the shocks could be avoided.

Responding under fixed‐ratio schedules was studied as a function of two durations of food presentation. Latency of the first response after food presentation (post‐reinforcement pause) was consistently shorter when food was presented for the longer duration. Only one of the four pigeons studied showed a consistently higher response rate, exclusive of post‐reinforcement pause, as a function of the longer access to food. When ratio size was reduced, pause durations decreased, and the differences related to the two durations of food presentations became progressively smaller.

Eight albino rats, conditioned to press a lever to escape shock, continued to lever press during short inescapable shocks presented subsequently. The rate of this behavior was found to be higher for higher shock intensities regardless of the order in which shock values were presented. Relative to the immediately preceding escape rate, responding during inescapable shock was higher following conditioning at higher fixed‐ratio escape requirements. Four subjects not conditioned to escape shock pressed the lever very infrequently during inescapable shock and showed little change with changes in shock intensity. The escape conditioning effects suggest that responding during inescapable shock is superstitious escape behavior. The effects of shock intensity on this behavior appear to be similar to reported effects of shock intensity on escape behavior.

Six college students participated in matching‐to‐sample tasks. Conditioned emotional response (CER) training consisted of pairing a tone with a “painful” level of shock. Three of the subjects demonstrated response suppression, one subject showed facilitation, and two showed no change. Analysis of response rate during the tone interval indicated that, for those subjects who showed response suppression, the decrease in response rate was greatest immediately before onset of the unconditioned stimulus. This temporal discrimination was similar to that obtained with infrahumans.