Behavioral contrast for key pecking as a function of component duration when only one component varies

Pigeons pecked keys for food reinforcers delivered by multiple variable-interval 2-min variable-interval 2-min schedules. Positive behavioral contrast was created by changing one component to extinction; negative contrast was achieved by changing one component to a variable-interval 15-s schedule. The duration of each component was varied independently of the other from 5 to 960 s. The size of positive contrast was greatest when the extinction component was 30 or 60 s long. It did not change significantly with changes in the duration of the variable-interval 2-min component. The absolute size of negative contrast decreased with increases in the duration of the variable-interval 2-min component. It did not change significantly with changes in the duration of the variable-interval 15-s component. These results show that the size of contrast is determined primarily by the duration of the component that provides the less favorable conditions of reinforcement. These results are not predicted by current theories.     

Behavioral contrast as a function of the temporal location of reinforcement

Pigeons were trained on a multiple variable-interval variable-interval schedule of reinforcement. One component was then changed to a variation of a fixed-interval schedule in which the same rate of reinforcement was obtained as previously but the location of the reinforcer was fixed within the component. The effects of different temporal locations were compared. An increase in response rate for the unchanged variable-interval component (behavioral contrast) occurred when the reinforcer was located in the middle or at the end of the FI component, but response suppression occurred when it was located at the beginning of the component. The pattern of results cannot be explained by any previous theories of contrast. The overall response rates, and the pattern of local rates within the components, were consistent with the hypothesis that the major determinant of the contrast effect was the transition to a lower reinforcement rate following the unchanged component.     

Behavioral contrast with timeout, blackout, or extinction as the negative condition

When either a timeout period (darkening the response key) or a blackout period (darkening both chamber and response key) was alternated with a stimulus associated with variable-interval reinforcement, behavioral contrast was obtained. Either peck contrast or maintained contrast occurred, depending on whether or not responding was evidenced during the negative condition. These results are contrary to recent accounts emphasizing the role of non-reinforced responding in the production of contrast, but are consistent with interpretations emphasizing the aversiveness of the negative condition.     

Behavior in a novel situation as influenced by the immediately preceding environment

Behavior in a novel situation, which basically represented an increase in complexity for some Ss and a decrease in complexity for others, was sampled by the use of an exhaustive list of response categories at 5-sec intervals for 24 min. Wide behavioral differences are described. In addition, the feasibility of the time-sampling technique for the study of animal behavior is further demonstrated, and its more general use is advocated.     

Behavioral engineering: stuttering as a function of stimulus duration during speech synchronization

Past studies have shown that stuttering is eliminated when speech is synchronized with a metronomic beat, but the speech sounds artificial. The present study investigated the effect of increasing the duration of these individual stimulus beats with the stimulus-off period constant at 1 sec. When subjects were instructed to speak during the stimulus-on period, stuttering was an inverse function of stimulus duration, indicating that the known metronome effect on stuttering is one point on a continuum of effective rhythm procedures. The "naturalness" of speech increased as the stimulus duration increased up to durations of about 2 sec, and then decreased. At optimal values, stuttering was greatly reduced and naturalness and rapidity of speech were retained. These optimal values effectively controlled stuttering in a field test that used two types of specially designed portable instruments, one of which produced a tactual stimulus and the other an auditory stimulus.     

Behavioral contrast in fixed-interval components: effects of extinction-component duration.

Seven albino rats were exposed to a multiple schedule of reinforcement in which the two components (fixed interval and extinction) alternated such that a presentation of the extinction component followed each fixed-interval reinforcement. In baseline sessions, the duration of the extinction component was constant and always one-third of the fixed-interval value. Probe sessions contained a probe segment in which the duration of the extinction component was increased; the response rate in fixed-interval components during the probe segment was compared with the response rate in the segments preceding and following the probe. The effect of increasing the duration of the extinction component was studied under three values of fixed interval: 30 s, 120 s, and 18 s, in three successive conditions. Response rate within fixed intervals was a direct function of duration of the extinction component. Pausing at the beginning of the fixed interval decreased as extinction duration increased. These effects were larger and more consistent for the shorter fixed-interval values (18 s and 30 s). These results indicate a functional relation between relative component duration and responding. For the component providing more frequent reinforcement, this could be stated as an inverse relationship between relative component duration and response rate. This relation is similar to findings regarding the ratio of trial and intertrial duration in Pavlovian conditioning procedures, and suggests that behavioral contrast may be related to Pavlovian contingencies underlying the multiple schedule.     

Positive and negative contrast as a function of component duration for key pecking and treadle pressing

Pigeons responded on several multiple schedules for food reinforcers. The duration of the components varied from four seconds to 16 minutes. The absolute size of positive (Experiment 1) and negative (Experiment 2) behavioral contrast varied inversely with component duration when key pecks produced the reinforcers. The absolute size of negative contrast varied directly with component duration, when treadle presses produced the reinforcers (Experiment 3). These results conform to theories that suggest that positive and negative contrast are symmetrical when pigeons peck keys. They also conform to theories that suggest that the same principles do not govern contrast when pigeons peck keys as when they press treadles. Finally, the results support the measurement of behavioral contrast by the differences between baseline rates of responding and the rates emitted when contrast is present.     

Behavioral contrast as differential time allocation

In Experiment I, hooded rats were exposed to multiple variable-interval schedules of reinforcement in which manipulanda and reinforcement magazines at opposite ends of the experimental chamber were associated with the different components. Time allocated to each component was measured by recording the time spent by the subject in the appropriate half of the chamber. Positive behavioral contrast was observed for the comparison between multiple variable-interval 30-second variable-interval 30-second and multiple variable-interval 30-second variable-interval 90-second conditions for both response frequency and time allocation measures, but not for mean local response rate (response frequency per time allocated to a component). In Experiment II, rats were exposed to multiple variable-time schedules in which reinforcement was response independent. Time allocated to each component was measured for two conditions, multiple variable-time 30-second variable-time 30-second and multiple variable-time 30-second variable-time 90-second. Positive behavioral contrast of time allocation was exhibited. The results indicated that time allocation was differentially sensitive to changes in reinforcement probability, and that behavioral contrast may result from the differential allocation of time to the different components of the multiple schedule.     

Perceived duration as a function of pitch

It was demonstrated with 7 observers that the duration of a high frequency tone was perceived to be longer than the duration of a low frequency tone, even though the actual duration of the two tones was equal.     

Behavioral contrast in one component of a multiple schedule as a function of the reinforcement conditions operating in the following component

The key pecks of four pigeons were reinforced on a variable-interval 5-min schedule which operated in each of the four components of a multiple schedule, indicated by red, green, yellow, and blue stimuli and presented in such an order that the red stimulus always preceded the yellow and the green stimulus always preceded the blue. After establishing baseline rates, the reinforcement schedule associated with the blue and yellow components was altered so that one was now an extinction schedule and the other was a variable-interval 1-min schedule. In a second experimental stage, the blue stimulus was interchanged with the yellow so that the red stimulus preceded the blue and the green stimulus preceded the yellow. In both experimental stages the response rate in the variable-interval 5-min component that preceded the extinction component was higher than the response rate in the variable-interval 5-min component that preceded the variable-interval 1-min component. The results were discussed in relation to the importance of stimulus ordering in experiments concerned with investigating behavioral contrast.     

Phoneme-monitoring reaction time as a function of preceding intonation contour

An acoustically invariant one-word segment occurred in two versions of one syntactic context. In one version, the preceding intonation contour indicated that a stress would fall at the point where this word occurred. In the other version, the preceding contour predicted reduced stress at that point. Reaction time to the initial phoneme of the word was faster in the former case, despite the fact that no acoustic correlates of stress were present. It is concluded that a part of the sentence comprehension process is the prediction of upcoming sentence accents.     

Facilitation of extinction by an increase or a decrease in trial duration

Five experiments examined the effects of altering the duration of a conditioned stimulus (CS) for extinction. For the first 3 experiments, rats received conditioning with a 10-s CS before different groups received extinction with a CS that was either the same duration or longer than that used for conditioning. For the remaining 2 experiments, conditioning was conducted with a 60-s CS before different groups received extinction with a CS of either the same duration or a shorter duration than that used for conditioning. In all experiments, extinction progressed more readily when the CS duration was different for the 2 stages than when it was constant. The results are discussed in terms of rate expectancy theory and associative learning theory.