No abstract

Temporal control of behavior was investigated within the framework of an internal clock model. Pigeons were exposed to signaled fixed-interval 30-s trials mixed with extended unreinforced (baseline) trials. On unreinforced break trials, the signal was interrupted for a period of time after trial onset. In Experiment 1, comparisons between the peak time obtained on baseline and on break trials produced peak time shifts that were longer than those expected if the clock had stopped during the break but shorter than if the clock had reset. In Experiment 2, systematic manipulations of duration and location of breaks produced peak time shifts that were nonlinear functions of break duration and that varied linearly with break location. The obtained peak times were more consistent with a continuous memory decay model than with the stop-retain or the reset hypotheses.

When the schedule of reinforcement in 1 component of a multiple variable interval/variable interval (mult VI/VI) schedule is changed to extinction, pigeons typically show an increase in rate of key-peck responding in the unchanged component. This effect has been labeled behavioral contrast. In the present study, pigeons were reinforced for depressing a foot treadle according to mult VI/VI schedules. After rates of responding stabilized, the schedule in 1 component was changed to extinction. This manipulation resulted in either no change or a decrease in rate of responding in the unchanged component. The birds were then reinforced for key pecking under the same procedure. When key pecking was the operant, the experimental manipulation resulted in behavioral contrast. The results are discussed in terms of Pavlovian/instrumental interactions.

Control of pigeons' keypecking by a stimulus-reinforcer contingency was investigated in the context of a four-component multiple schedule. In each of three experiments, pigeons were exposed to a schedule consisting of two two-component sequences. Discriminative stimuli identifying each sequence were present only in Component 1, which was 4, 6, or 8 sec in duration, whilereinforcerscould be earned only in Component 2 (30 sec in duration). Control by a stimulusreinforcer contingency was sought during Component 1 by arranging a differential relation between Component 1 cues and schedule of reinforcement in Component 2. In Experiment 1, rate of keypecking during Component 1 varied with the presence and absence of a stimulus-reinforcer contingency. When a contingency was introduced, rate of keypecking increased during the Component 1 cue associated with the availability of reinforcement in Component 2. In Experiment 2, the stimulus-reinforcer contingency was manipulated parametrically by varying the correlation between Component 1 cues and Component 2 schedules of reinforcement. Responding in Component 1 varied as a function of strength of the stimulus-reinforcer contingency. The relatively high rates of Component 1 responding observed in Experiments 1 and 2 pose difficulties for conceptions of stimulus-reinforcer control based on probability of reinforcement. In these two experiments, the stimulus-associated probabilities of reinforcement in Component 1 were invariant at zero. An alternate dimension of stimulus-reinforcer control was explored in Experiment 3, in which Component 1 cues were differentially associated with delay to reinforcement in Component 2, while probability of reinforcement was held constant across components. When the stimulus-reinforcer contingency was in force, rate of responding in Component 1 varied inversely with delay to reinforcement in Component 2. In a quantitative analysis of data from Experiments 2 and 3, relative rate of responding during Component 1 was strongly correlated with two measures of relative delay to reinforcement.The acquisition and maintenance of keypecking in pigeons under autoshaping procedures (Brown & Jenkins, 1968; Williams & Williams, 1969) suggest that responses sensitive to operant contingencies can also be controlled by a stimulus-reinforcer (S-SR) contingency. Subsequent to this early work, many studies have been reported in which keypecking was shown to vary when some dimension of S-SR relation was changed (e.g., Gamzu & Schwartz, 1973; Garnzu & Williams, 1971, 1973Gibbon, Locurto, & Terrace, 1975;Hemmes, 1973). An issue which is becoming increasingly evident in this literature is a lack of consensus on the manner in which the S-SR relation is specified. Gamzu and Schwartz (1973), for example, reported that rate of keypecking under a responseindependent multiple schedule varied with relative rate of stimulus-associated food presentation.Thisresearch wassupportedby PSC/BHE Grant 13015 and by NIH Grant RR07064 to the first two authors. We wish to thank ElkanGa...