THE ACCENTUA TION OF A RATE DIFFERENCEDURING EXTINCTION'

L. R. GOLLUB2 and J. T. URBAN

HARVARD UNIVERSITY

It is usually said that the performance in the presence of any one stimulus of amultiple schedule3 is essentially the same as the performance under that singleschedule (Ferster & Skinner, 1957). This similarity is found under a wide range ofschedule variations. Under mult FI FR, where each component is a member of adifferent class of schedules, a scallop usually appears in the interval component,and the typical high rates of responding in the ratio. However, some characteristicsof the performance are affected by the other member of the multiple schedule. Forexample, the initial pause in the FI is affected by the number of preceding ratio seg-ments, and is usually longer after several ratios have been completed. Interactionssuch as these have been shown by Dews (1956) and by Ferster and Skinner (1957).The performance may also be changed when the components are from the same

class of schedules, as in mult VI VI. The continuous, moderately high rates of re-sponding usually found under a single VI schedule also occur in each component.The type of interaction between these similar schedules may be between the ratesrather than between the patterns of responding.

In the present experiment, the interaction has been studied between componentsfrom the same class of schedules but with different values, mult VI 3 VI 9. Thepigeons reinforced under this schedule were also run at several levels of bodyweight, to study the effect of deprivation on the schedule interaction. Finally, re-sponding was extinguished under both stimulus conditions.

SUBJECTS AND PROCEDURE

The subjects were four adult male White Carneau pigeons. Two of these (S1 andS2) had been exposed to several VI schedules, while the other two (S3 and S4) hadbeen run for only 20 sessions on VI 6 prior to this experiment.

All birds were first reinforced on VI 6 for several sessions in a standard pigeonapparatus (Ferster & Skinner, 1957). The schedule was then changed to mult VI 3VI 9, with the key illuminated by blue and orange lights according to the schedulewhich was programmed. The schedules changed after 15 minutes of VI 3 and45 minutes of VI 9. The result was that, on an average, an equal number of rein-forcements was programmed during each stimulus, and the mean inter-reinforce-ment time over the session was kept at 6 minutes. Two consecutive daily sessionswere followed by a rest of 2 days for a total of 10 sessions. During this period, twodifferent states of food deprivation were maintained: on one of each pair of days

'This work was supported by a grant from the National Science Foundation. The authors thankDrs. B. F. Skinner and W. H. Morse for their aid and advice.

2Predoctoral Fellow of the National Science Foundation.3In a multiple schedule, "reinforcement is programed by two or more schedules alternating..., each

schedule being accompanied by an appropriate stimulus as long as the schedule is in force." (Ferster &Skinner p. 729). In mult Fl FR, for example, the response key is illuminated by light of one color whenresponding is reinforced according to Fl, and by a different color when FR is in force.

365

L. R. GOLLUB and J. T. URBAN

the bird's body weight was high (about 90-95 per cent of free-feeding weight); onthe other day, the body weight was low (about 75 per cent).

Responding in the presence of each stimulus was then extinguished. During ex-tinction the stimuli were alternated every 12.5 minutes, and the session lasted untilresponding in each stimulus fell to a low level. Extinction took between 10 and17 hours.

RESULTS

"Typical" VI performances developed in each component of the multipleschedule-the rate of responding in the presence of each stimulus was approxi-mately constant throughout a session, and the rate was somewhat higher in thepresence of the VI 3 stimulus than in the presence of the VI 9 stimulus. Table 1summarizes the rates under the several VI schedules. The mean rates of respond-ing under the single VI 6 schedule and the VI 9 component of the multipleschedule were about the same, while the rate under VI 3 was somewhat higher.The range of the daily mean rates reflects, in part, the changes produced by body-

TABLE 1

Comparison of V16 with Mult VI3 V19

(Mean Rate andResponses

Subject

S 1

S2

S3

S4

VI 3

87

56

109

51

Range of Rates;per Minute)

VI 6

Mean Rate

55

43

74

45

Range of Rates

65-108

49-72

56-124

47-61

38-59

60-92

46-64

32-51

27-107

39-68 37-53

VI9

53

42

76

43

S1

S2

S3

366

S4 29-54

RATE DIFFERENCE DURING EXTINCTION

weight manipulations. The rates of responding in both components were higher atthe lower body weight, but the rates in the two components were not affecteddifferentially by degree of deprivation.

Responding during extinction in the presence of each of the alternating colorsoccurred with the smoothly declining rate characteristic of extinction after shortexposure to VI. Figure 1 shows the first 8 hours of the extinction session for onebird (S4). Responding in the presence of the stimulus previously correlated withVI 3 is shown in Record A, and with VI 9, in Record B. Note that the recordshave been aligned so that they begin at the same point in time, and that Record Ahas been displaced about 300 responses above Record B. Initially, the rate in theVI 3 stimulus was slightly higher than the rate in the VI 9 stimulus. The differencein the rates increased during the session as the rate in VI 9 declined. The rate in theVI 3 stimulus also declined, but only after a longer period of sustained respondingduring several presentations of the stimulus. Altogether, the bird emitted 3.3 timesas many responses in the VI 3 stimulus as in the VI 9 stimulus. In the multipleschedule the ratio of the rate in VI 3 to the rate in VI 9 had been 1.16.

After the rates in both stimuli declined to very low values, gradual increases inrate appeared during some presentations of the VI 3 stimulus, as before a and c inthe detail of Fig. 1. The arrows above the curve in Record A indicate when the stim-ulus was changed. Two other birds showed a similar cyclic effect.

Table 2 (Column 2) summarizes the extinction results for all subjects. Column 1is the ratio of the rate in the VI 3 component to the rate in VI 9 for the last two

TABLE 2

Ratios of the Performance

in the Components of a Multiple Schedule during

Intermittent Reinforcement and Extinction

Intermittent ExtinctionReinforcement

VI 3 rate No. VI 3 responsesSubject

VI 9 rate No. VI 9 responses

S 1 1.52 4.72

S 2 1.23 3.92

S 3 1.66 2.46

367

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L. R. GOLLUB and J. T. URBAN

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sessions of the multiple-schedule procedure. Comparison of Column 2 with Col-umn 1 shows that the ratio of the performances in the two components differs morein extinction than during intermittent reinforcement for all four birds. Cumulative-response records revealed that the greater difference in extinction resulted bothfrom a higher initial rate and a longer sustained period of responding in the VI 3stimulus.The pairs of birds with different experimental histories also showed a character-

istic difference. Birds S1 and S2, with more extensive experimental histories, showeda greater difference in extinction in the presence of the two colors than did S3 andS4. Also, they emitted a larger total number of responses in extinction than the lessexperienced pair.

DISCUSSION AND SUMMARY

Four pigeons were first reinforced under mult VI 3 VI 9, and responding was thenextinguished under the two stimulus conditions. The ratio of the rates in the twostimuli differed more during extinction than during the period of intermittent rein-forcement. Although the rate of responding during intermittent reinforcement wasslightly higher in the component with the greater frequency of reinforcement, a stillgreater difference between the rates of responding in the two stimuli occurred in ex-tinction. There are no normative data to show whether the ratio of the rates underthe same simple schedules is more similar to the ratio obtained under the multipleschedule, or to the ratio of rates during extinction. The magnitude of the interactionunder the multiple schedule is therefore impossible to identify quantitatively. How-ever, the clear difference between the pairs of ratios obtained in the present experi-ment indicates that effects produced by a selected variable are a function, also, ofthe conditions under which they are obtained.

REFERENCESDews, P. B. Modification by drugs of performance on simple schedules of positive reinforcement.

Ann. N. Y. A cad. Sci., 1956, 65, 268-28 1.Ferster, C. B., and Skinner, B. F. Schedules of Reinforcement. New York: Appleton-Century-

Crofts, 1957.

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