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Transfer between downshift in reward magnitude and continuous delay of reward
LEARNING
AND
MOTIVATION
Transfer
6, 241-252 (1975)
Between and
Downshift
Continuous
in Reward
Delay
Magnitude
of Reward
MITRI E. SHANAB AND HUGH J. FERRELL California
State
University.
Fresno
Two separate experiments were conducted to investigate transfer of persistence between delay and a downshift in reward magnitude. In the first experiment, experimental rats were initially downshifted in reward magnitude and later tested for persistence to continuous delay of large reward. It was found that these rats were more persistent to the effects of delay than control rats which did not receive prior experience with a downshift in reward magnitude. In the second experiment, experimental rats were first trained to receive large reward under delayed conditions and then tested for persistence to a downshift in reward magnitude. Compared to control rats which received no prior experience with delay, the experimental rats showed a significantly smaller negative contrast effect. The results were interpreted as supporting Amsel’s theory of persistence as well as Capaldi’s recent interpretation of contrast effects.
Amsel(1972) has proposed a general theory of behavioral persistence based on the principle of counterconditioning. According to this view, persistence occurs whenever an organism learns through counterconditioning to maintain an instrumental response under conditions which normally disrupt or interfere with the learned response. One form of persistence is reflected in the partial reinforcement extinction effect (PREE). Subjects receiving partial reward (Robbins, 1971), partial delay of reward (Donin, Surridge & Amsel, 1967), partial punishment (Brown & Wagner, 1964; Dyck, Mellgren & Nation, 1974; Fallon, 1968), or partial reinforcement during escape conditioning (Seybert, Mellgren, Jobe & Eckert, 1974; Woods, Markman, Lynch 8c Stokely, 1972) show greater resistence to extinction (i.e., persist longer) than control subjects trained under continuous reinforcement conditions. The persistence obtained in such studies is attributed to the fact that although frustration produced by partial reinforcement and partial delay of reinforcement and fear produced by punishment or escape conditioning, initially evoke competing responses which interfere with the goalapproach response, the stimuli arising from these frustration and fear Supported in part by faculty research grant (No. 3025.07) awarded to the first author. Reprint requests should be sent to Mitri E. Shanab, Department of Psychology, California State University, Fresno, CA 93740. Present address of Hugh J. Ferrell: Department of Psychology, Purdue University, Lafayette, IN. 241 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
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responses become counterconditioned to the goal-approach response. The PREE suggests that persistence learned under one disruptive or aversive situation (e.g., partial reinforcement, delay, punishment, etc.) transfers to another disruptive situation (viz., extinction). Studies have shown that transfer of persistence is not limited to the above situations. Brown and Wagner ( 1964) reported significant transfer between fear and frustration, in that subjects trained under partial reinforcement and tested under continuous punishment conditions or subjects trained under partial punishment conditions and tested in extinction showed greater persistence than control subjects trained under continuous reinforcement conditions. These results have since been replicated (Linden & Hallgren, 1973). Significant transfer has also been reported between fear of electric shock and loud noise (Terris & Wechkin, 1967). between frustration produced by partial reinforcement and partial goal blocking (Glazer & Amsel, 1970), and between frustration produced by partial reinforcement and partial delay of reinforcement and continuous delay of reinforcement (Shanab, 1971; Shanab & Cavallaro, 1973). These findings offer strong support to the commonality hypothesis of persistence effects (Wagner. 1969; Amsel, 1972). By assuming that frustration and fear have similar underlying mechanisms, the commonality hypothesis can reasonably explain the obtained transfer between responses learned under either frustration or fear-producing conditions. Specifically, persistence is mediated by the conditioned frustration (rF - sF) and the condition punishment or fear (r, - sp) mechanisms. Initially, the internal stimuli associated with the frustration and fear responses (sF and sp) evoke competing responses but eventually become counterconditioned to the ongoing goal-approach response. A simple implication of the commonality hypothesis is that various frustration-producing operations are governed by the same underlying mechanism. Thus, the conditioned frustration (rr - sF), or persistence, mechanism has been used to account for the PREE following partial reinforcement or partial delay as well as for transfer between nonreward and either delay or blocking of reward (Amsel, 1972; Shanab, 197 1). The two experiments reported here were designed to test further implications of this hypothesis. EXPERIMENT
I
Ebiperiment I was performed to test the hypothesis that rats having prior experience with a downshift in reward magnitude would persist longer than control rats when all rats receive large reward after some delay interval. Specifically, two large-rewarded groups and one smallrewarded group were run initially. Then one large-rewarded group was shifted to small reward in an effort to obtain a negative contrast effect
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(NCE) while the other continued to receive the same large reward. The rats were then tested for persistence to continuous delay. During the test phase, all rats received large reward after a 15set delay interval. According to frustration theory, all rats should experience frustration during this phase. Therefore, those rats which had already learned persistence during the downshift phase would persist longer than either the nonshifted large-reward or small-reward rats. However, the same objection raised earlier by D’Amato (1969) concerning the Brown and Wagner (1964) results is applicable to the present study. The predicted outcome could be attributed not only to prior experience with frustration but to a possible positive contrast effect (PCE) based on a shift from small to large reward. Therefore, the present experiment included a control phase which preceded the test phase, in which each rat received large immediate reward on each trial. Thus, as Linden and Hallgren (1973) suggested, any PCE would be observed and allowed to run its course before the test phase for persistence would be started. Method Design. The experiment consisted of four phases. In Phase 1, the rats received either large or small reward without delay. In Phase 2, half of the large rewarded rats continued to receive large reward (Group LL) while the other half (Group LS) was shifted to the same small reward received by the small rewarded rats (Group SS). All rats received large immediate reward in Phase 3, but in Phase 4 they received the same large reward after a 15set delay interval. Subjects. Thirty-three naive male albino rats of the Sprague-Dawley strain were used. The rats were approximately 60 days old when received from the Simonson Laboratories, Gilroy, CA. Apparatus. A 1.5-m runway made of unpainted redwood was used. The runway was covered with Plexiglas and was 23 cm high and 10 cm wide throughout. The startbox was I8 cm long and 17 cm wide. The goalbox was L-shaped. The initial section of the goalbox was 30.5 cm long and 15 cm wide. At right angles to this section was a 16 X 16 cm section in which the foodcup was placed. This prevented the rat from making any visual discrimination as to whether or not the foodcup was baited. Four sets of photocells were installed in the runway. Interruption of any of the four photobeams started and/or stopped any one of the three electric timers that measured start, run, and goal times. The first, second, third, and fourth photocells were located 6.5, 2 1.5, 103, and 115 cm from the startbox, respectively. The start- and goalboxes were separated by two guillotine doors. Procedure. Upon receipt from the supplier, the rats were placed in individual cages and had free access to food and water for thirty days. During
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this period, the rats were first weighed and then handled for 2 min a day. Thereafter all rats were given restricted food rations (approximately IO g per rat) and maintained at about 80% of their free-feeding weight, which level was reached by all rats within 14 days. Water was available freely throughout the experiment. Proper adjustment was made for food eaten in the experimental situation. Each rat was given its daily ration at least 30 min after its last daily trial. Throughout all phases of the experiment, the rats received three trials per day and were run in squads of three so as to maintain a short intertrial interval (IT1 = 3-5 min). To control for any visual cues the reinforcer was placed in the L-shaped section throughout the experiment. Pretraining started as soon as all rats reached their 80% level and consisted of allowing each rat to explore the unbaited runway for 90 set on each of three days. The equipment was turned off during the first day of exploration but was turned on during the second day in order to familiarize the rats with the different noises which would be present during regular training. On the third day of exploration, the rat’s first running times were recorded in an attempt to obtain an approximate operant level for each rat. In Phase 1, the rats were randomly assigned to two main groups. One group of 22 rats received large reward (20 45mg pellets) whereas the other group of 11 rats received small reward (two 45mg pellets). This phase lasted 48 trials. In Phase 2, the rats in the large-rewarded group were subdivided randomly into two equal groups. One subgroup (Group LL) continued to receive large reward (20 pellets) while the other (Group LS) received small reward (two pellets). The control rats (Group SS) continued to receive small reward (two pellets). This phase lasted 2 1 trials. Following stable performance in Phase 2, all rats were given large immediate reward for 21 trials (Phase 3). Finally, in Phase 4, all rats received large reward following a 15set delay interval. The rats received 27 such trials in this phase. On these trials, they were detained in the terminal section of the runway for 15 sec. following which they were allowed to enter the Lshaped section and receive the reinforcer which had just been placed. Results All analyses are based on total running speed which was obtained by multiplying the reciprocal of the sum of the start, run, and goal times by the total distance (1.27 m) traversed by each rat. Phase I. A one-way analysis of variance test was performed on the last three blocks using the downshifted group as a dummy factor. There was no significant main effect (F(2,30) < 1) . Phase 2. As Fig. 1 shows, the large rewarded group showed a marked
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tr101s
1. Mean total speed in Phase 2 (downshift), Phase 3 (recovery), and Phase 4 (delay).
decrement in performance when first shifted to small reward. This decrement was, however, overcome by the fifteenth trial. Two separate analyses of variance were performed to verify the visual analysis. The results of the analysis of variance test over the first 12 trials yielded significant main effects (F(2,30) = 10.85, p < .OOl). Individual comparisons showed that Group SS ran significantly faster than Group LS reflecting a reliable NCE (F( 1,30) = 13.72, p < .OOl). The difference between Groups LL and SS was not significant (F ( 1,30) < 1) . On the other hand, Group LL ran significantly faster than Group LS (F( 1,30) = 18.53, p < .OOl). An analysis of variance performed on the last three blocks yielded nonsignificant results (F(2,30) < 1). The same test performed on the last block yielded similar results (F(2,30) < 1). Phase 3. Figure 1 shows that when all subjects were immediately reinforced on each trial during this phase, Group LS ran consistently faster than Group LL, reflecting a possible positive contrast effect (PCE). The statistical analysis, however, did not confirm this graphical effect. Separate analyses of variance were done on each block, each yielding nonsignificant results. The results of the last block of this phase is typical (F(2,30) < 1). Similarly, the results of an analysis of variance with repeated measures performed on Blocks 2-7 yielded nonsignificant effects (F(2,30) = 1.80, p > .05 for treatment; t;(5,150) < 1 for blocks, and F( 10,150) < 1 for the interaction of blocks and treatment). The latter two findings indicate that the performance of each group was stable over almost all of Phase 3. Phase 4. As can be seen in Fig. 1, when all rats were delayed in Phase 4, their speeds dropped accordingly. However, Group LS ran faster than Group LL during the initial part of the phase. The performance of the different groups converged by Block 4 and showed a slight recovery
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thereafter. An analysis of variance with repeated measures over Blocks l-4 yielded a significant main effect (F(2,30) = 6.08, 17 < .Ol). The blockseffectwashighlysignificant (F(3,90) = 43.53,~ < .OOl). However. the interaction of the two variables was not significant (F(6,90) = .94. p > .OS). Individual comparisons showed that Group LS ran significantly faster than both Groups LL and SS (Fs( 1,30) = 10.82 and 7.31, ps -=c.005 and .025, respectively). However, the results of an analysis of variance test on Block 4 were not significant (F(2,30) < 1). On the other hand, separate analyses of variance significant (F(2,30) < 1). On the other hand, separate analyses of variance were performed on each one of the first three blocks of this phase. The first trial of the first block was excluded from the analysis on the grounds that it could be considered a regular trial in Phase 3. The results of all three tests were significant (F(2,30) = 3.74, p < .05 for the first block, F(2,30) = 7.83, p < .Ol for the second block, and F(2.30) = 3.45, p < .05 for the third block). Finally, Blocks 4-9 were subjected to an analysis of variance test which yielded nonsignificant results F( 2.30) < 1. EXPERIMENT
11
Experiment II is the complement of Experiment 1. Using the same reasoning employed earlier, the commonality hypothesis leads to the prediction that rats with prior experience with delay of reinforcement would show greater persistence when downshifted in reward magnitude than control rats not having had experience with delay. Method Design. In Phase 1, 22 randomly chosen rats received immediate large reward while a second random group of 11 rats received immediate small reward. In Phase 2, a random half of the large-rewarded Ss received their reinforcer after a 15-set delay interval (L,) while the other half continued to receive their reinforcer without delay (LND). The small rewarded rats also received immediate reinforcement (S,,). In Phase 3, delay was removed and all three groups received their respective rewards immediately. All rats in Phase 4 received small immediate reward. The third phase was intended to control for any positive contrast effects that might occur as a result of shifting rats from delay to nondelay, thus ruling out the possibility that previously delayed rats persist longer than nondelayed rats during a downshift in reward magnitude merely because the delayed rats experience positive contrast when shifted to no delay. Subjects. The rats were 33 naive male albino rats of the SpragueDawley strain and were approximately 60 days old upon arrival from the supplier. Apparatus. The apparatus used was the same as that used in Experiment I.
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Procedure. The same general procedure concerning handling, deprivation, number of trials per day, ITI, etc., which was used in Experiment I was also used in this experiment. The magnitude of reward was also the same (either twenty 45mg or two 45mg pellets), as was the delay interval (15 set). Resu Its
All analyses are based on total speeds. Phase I. An analysis of variance with repeated measures performed on the last three blocks yielded nonsignificant effects. The delayed group was included as a dummy factor. The main effect of magnitude was not significant (F(2,30) = 1.98, p > .OS). Neither the blocks nor the magnitude by blocks interaction effects were significant (F(2,60) < 1, and F(4,60) < 1, respectively) indicating that all subjects had reached a stable and comparable level by the end of the phase. Phase 2. As Fig. 2 indicates, subjects in Group L, showed a marked decrement in performance when first shifted to delay and continued to perform at a greatly depressed speed level throughout all 24 trials of the phase. This is supported by the results of several analysis of variance tests performed on the mean speeds over Block 2 alone, Blocks 1-8, Blocks 2-8, Blocks 6-8, and Block 8 alone. All tests showed significant main effects. The results of the analysis of the first and last blocks, for example, yielded the following: Fs(2,30) = 4.77 and 22.77, ps < .05 and <.OOl for Block 1 and Block 8, respectively. Individual comparisons showed that rats in Group S,, as well as those in Group L,, ran significantly faster than Ss in Group L,(Fs(l,30) = 21.64 and 43.54, both ps < .OOl). The analyses of variance on the other blocks yielded F values that were significant at the .OOl level or better. Phase 3. When delay was removed, the performance of Group L, showed a gradual recovery and eventually reached the level of the 1.25
Pha 4 Phas , 3
Phosez
0
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Blocks
FIG. 2. Mean
total speed in Phase 2 (delay),
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of ,tlree
trials
Phase 3 (recovery),
and Phase 4 (downshift).
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nondelayed groups. An analysis of variance test performed on the last three blocks yielded a nonsignificant main effect (F(2,30) = I. 16, p > .05). The same test done on the last block of this phase showed similar results (F(2,30) = 1.80, p > .OS). Phase 4. Figure 2 shows that the shift to small reward resulted in different performance-decrement rates for Groups L,, and L,. The rats in Group L, appear initially to have decreased their speeds less rapidly than those in Group L,,. This conclusion is supported by the results of a repeated-measures analysis of variance test performed on the first four blocks. The treatment effect was highly significant (F(2,30) = 1 I .39, p < .OOl). Both the blocks and the blocks by treatment effects were significant (F(3,90) = 13.94, p < .OOl and (F(6,90) =4.53, p < .OOl. respectively). The latter supports the graphical conclusion that the observed performance decrement was dependent upon the prior treatment received by the rat. Individual comparisons showed that both Groups L,, and L, ran significantly slower than Group S,,(P( 1,30) = 22.70, p < .OOl, and F(1,30) = 5.88, p < .OS, respectively). Moreover, Group L, ran significantly faster than Group L,, (F( 1,30) = 5.47, p < .05). As Fig. 2 shows, the difference in performance decrement between Groups L,, and L, disappeared by Block 5. The results of an analysis of variance test on Blocks 5 and 6 combined yielded a significant main effect (F(2,30) = 7.53, p < .Ol). Individual comparisons showed that both Groups L,, and L,, ran significantly slower than Group S,,(Fs( 1,30) = 12.53 and 9.98, both ps < .OOl, respectively). No significant difference was detected between Groups L,, and L,, (F( I ,30) < 1) . Finally, as Fig. 2 indicates, all groups converged to a common level by the end of the phase. This conclusion is supported by the results of two analyses of variance. One test which was performed on the last three blocks yielded a nonsignificant main effect (F(2.30) = 3.21, p > .05, whereas the other test performed on the last block yielded similar results (F(2,30) = 1.50, p > .05). Discussion
In both experiments, the obtained negative contrast was short-lived. This is in agreement with the findings of several studies (viz. Spear & Spitzner, 1968; Capaldi, 1972; Capaldi & Singh, 1973). On the other hand, both experiments showed that delay produced marked and lasting decrements in performance. To be sure, the delayed subjects showed a slight recovery, but their performance stabilized at a significantly lower level than the nondelayed control subjects. One obvious implication of this asymmetry is that the two operations of delaying reward and reducing reward magnitude have different behavioral consequences: this probably accounts for the differential transfer
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effects obtained in the two studies. A second and probably more important implication is that the rather permanent decremental effects of delay could account for the relative permanence of the positive contrast effect obtained in studies which use delay as a procedure for ceiling effects (Mellgren, 1971; Mellgren, Seybert, Wrather & Dyck, 1973; Shanab. Birnbaum & Cavallaro, 1974). Both experiments showed that persistence learned under one frustration-producing condition transfers to a different frustration-producing condition. Thus, those rats which experienced a downshift in magnitude of reward showed greater persistence to delay of reward than those that did not have prior experience with a downshift in magnitude of reward (Experiment I). Similarly, rats with a history of delay of reward showed greater persistence to a downshift in reward magnitude than those that did not have such a history (Experiment II). Both findings confirm in general the earlier predictions based on Amsel’s theory of persistence (1972). Although the present experiments were designed to test certain implications of Amsel’s persistence theory, the results nevertheless are amenable to Capaldi’s (1972) latest interpretation of negative contrast effects. Earlier, Capaldi (1967) had proposed that the NCE is a function of generalization decrement experienced by the downshifted rats relative to the nonshifted rats. The NCE would not be permanent, because the rats would soon adjust to the absolute characteristics of the reward magnitude so that the aftereffects of the small reward (SRS) would become conditioned to the instrumental response, and the rat would eventually run at the same level as the control group. Recently, Capaldi (1972) attributed the NCE to four sources of generalization decrement associated with four unconditioned stimuli. Two of these stimuli, namely frustration stimuli (SF) and stimuli specific to the small reward magnitude (SRs) are ITIdependent in the sense that the intensity of such stimuli diminishes as the IT1 increases. The two other stimuli, S and S’“, are also associated with frustration and reward magnitude respectively but are not dependent on the ITI. Thus. according to this notion, only two sources of generalization decrement (Sf and Srs) contribute to NCE when trials are spaced but four such sources are involved when trials are massed (SF, SRS, Sf, and F). The obvious deduction, for which Capaldi (1972) provided ample evidence, is that the NCE would be larger following massed than spaced training. A second deduction leads to the prediction that little or no NCE would be expected in rats whose instrumental response had already been conditioned to one or more of these stimuli. In two separate studies (Capaldi & Lynch, 1967; Capaldi, 1972), it was found that while rats shifted from large to small reward showed a reliable NCE, those receiving the same treatment but with prior training with small reward showed no NCE. Ac-
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cording to Capaldi’s theory, the former group, called the nontransfer shift group, suffers four sources of generalization decrement (SF. Sf, SRS, and Srs), while for the latter, called the transfer shift group, two sources of generalization decrement (S” and Sf) presumably contribute to the NCE. Capaldi’s theory can thus account for the present findings by assuming that the stimulus aftereffects of frustration resulting from a downshift in reward magnitude are similar to those produced by delay. Thus for Experiment I this assumption implies that rats previously experiencing a reduction in reward magnitude would, when introduced to delay, experience a transfer shift (Group LS) while those introduced to the delay variable following a history of continuous immediate reward experience a nontransfer shift (Group LL). Similarly, in Experiment II, for those rats with prior experience with delay of reward a reduction in reward magnitude would constitute a transfer shift (Group L,,), but for rats that receive a downshift in reward magnitude without any prior experience with delay such an experience would constitute a nontransfer shift (Group L,,,). Thus the nontransfer-shift rats (Groups LL and L,,) should show less persistence during either delay or downshift in reward magnitude than transfer-shift rats (Groups LS and L,), which was the case in the present experiments. The lack of permanence of the persistence effects is in agreement with one major assumption of Capaldi’s theory, namely, that performance is a function of the absolute current characteristics of the reinforcement conditions. Thus, the performance of all rats regardless of their prior reinforcement history, should eventually come under the control of the current reinforcement conditions, thus according for the shortterm effects of the persistence effects in the present research. Finally, it should be noted that a closer examination of the results obtained in Phase 4 of both experiments reveals that the transfer effects obtained probably reflect partial transfer. This point can be made more clearly if the results of the second experiment are discussed first. In the latter experiment, rats with a prior history of delay also showed a negative contrast effect, which was of a lesser magnitude than the one observed in the nondelayed control rats. A full transfer effect would require that a NCE be observed in the control group only. Nonetheless, the significant transfer effects are consistent with the earlier predictions based on Amsel’s theory of persistence (1972). It was not expedient in Experiment I to run a second control group which received continuous delay all the time. Thus, although rats with a prior history of NCE were found to resist continuous delay longer than control rats not having had such experience (which confirms the hypothesis being tested), it is not known how the experimental rats would have performed relative to a second control group such as the one just described. In the absence of such a control
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group, it is probably more accurate to refer to the results of Experiment I as reflecting partial rather than full transfer. There are provisions in both Amsel’s and Capaldi’s theories to account for the partial transfer of persistence effects. According to Amsel, partial transfer would be attributed to similar but overlapping systems of persistence. In Capaldi’s recent terms, this effect could be accounted for by assuming that only frustrative stimuli (SF and Sf) are involved in the transfer between delay of reward and reductions in magnitude of reward. The specific stimuli associated with small reward (SRS and Srs) apparently do not contribute appreciably to the transfer of persistence between delay (SD and Sd) and downshifts in reward magnitude. In conclusion, it seems appropriate to point out the striking convergence of both the frustration and sequential theories towards a common explanation of behavioral phenomena (cf., Shanab & Birnbaum, 1974). With the admission of frustration stimuli, the sequential theory of Capaldi can now account for a variety of frustration-related phenomena that heretofore were more directly explicable in terms of frustration theory. REFERENCES Amsel,
A. Behavioral habituation, counterconditioning, and persistence. In A. Black and W. K. Prokasy (Eds.). Classical Conditioning II, New York: Appleton-Century-Crofts. 1972. Pp. 409-425. Banks, R. K. Persistence to continuous punishment following intermittent punishment training. Journal of Experimental Psychology. 1966, 71, 373-377. Capaldi, E. D., & Singh, R. Percentage body weight and the successive negative contrast effect. Learning & Motivation, 1973, 4, 405-416. Capaldi, E. J. A sequential hypothesis of instrumental learning. In K. Spence and J. T. Spence (Eds.), The psychology of learning and motivation: Advances in research and theory. Vol. 1. New York: Academic Press. 1967. Pp. 67-156. Capaldi, E. J. Successive negative contrast effect: Intertrial interval, type of shift, and four sources of generalization decrement. Journal of Experimental Psychology, 1972, 96, 433-438. Capaldi, E. J., & Lynch, D. Repeated shifts in reward magnitude: Evidence of an associational and absolute (noncontexual) interpretation. Journal of Experimental Psychology, 1967,75, 226-235. D’Amato, M. R. Instrumental conditioning. In M. H. Marx (Ed.) Learning Processes. Toronto: Macmillan, 1969. Pp. 35-l 18. Donin, J. A., Surridge, C. T., & Amsel, A. Extinction following partial delay of reward with immediate continuous reward interpolated at 24-hour intertrial intervals. Journal of Experimental Psychology, 1967, 1, 50-53. Dyck, D. G., Mellgren, R. L., & Nation, J. R. Punishment of appetitively reinforced instrumental behavior: Factors affecting response persistence. Journal of Experimental Psychology, 1974, 102, 125-132. Fallon, D. Resistence to extinction following learning with punishment of reinforced and nonreinforced licking. Jorlrnal of Experimental Psychology, 1968,76, 550-557.
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Glazer. H.. & Amsel. A. Transfer of persistence effects from frustration produced h! blocking to frustration produced by nonreinforcement. Prvc~lr~~rromic~ S~~i~~nc~e. I Y70. 18. 311-312. Linden. D. R.. & Hallgren, S. 0. Transfer of approach responding between punishment and frustrative nonreward sustained through continuous reinforcement. Lc,rrrrrirrv (in
AND
MOTIVATION
Transfer
6, 241-252 (1975)
Between and
Downshift
Continuous
in Reward
Delay
Magnitude
of Reward
MITRI E. SHANAB AND HUGH J. FERRELL California
State
University.
Fresno
Two separate experiments were conducted to investigate transfer of persistence between delay and a downshift in reward magnitude. In the first experiment, experimental rats were initially downshifted in reward magnitude and later tested for persistence to continuous delay of large reward. It was found that these rats were more persistent to the effects of delay than control rats which did not receive prior experience with a downshift in reward magnitude. In the second experiment, experimental rats were first trained to receive large reward under delayed conditions and then tested for persistence to a downshift in reward magnitude. Compared to control rats which received no prior experience with delay, the experimental rats showed a significantly smaller negative contrast effect. The results were interpreted as supporting Amsel’s theory of persistence as well as Capaldi’s recent interpretation of contrast effects.
Amsel(1972) has proposed a general theory of behavioral persistence based on the principle of counterconditioning. According to this view, persistence occurs whenever an organism learns through counterconditioning to maintain an instrumental response under conditions which normally disrupt or interfere with the learned response. One form of persistence is reflected in the partial reinforcement extinction effect (PREE). Subjects receiving partial reward (Robbins, 1971), partial delay of reward (Donin, Surridge & Amsel, 1967), partial punishment (Brown & Wagner, 1964; Dyck, Mellgren & Nation, 1974; Fallon, 1968), or partial reinforcement during escape conditioning (Seybert, Mellgren, Jobe & Eckert, 1974; Woods, Markman, Lynch 8c Stokely, 1972) show greater resistence to extinction (i.e., persist longer) than control subjects trained under continuous reinforcement conditions. The persistence obtained in such studies is attributed to the fact that although frustration produced by partial reinforcement and partial delay of reinforcement and fear produced by punishment or escape conditioning, initially evoke competing responses which interfere with the goalapproach response, the stimuli arising from these frustration and fear Supported in part by faculty research grant (No. 3025.07) awarded to the first author. Reprint requests should be sent to Mitri E. Shanab, Department of Psychology, California State University, Fresno, CA 93740. Present address of Hugh J. Ferrell: Department of Psychology, Purdue University, Lafayette, IN. 241 Copyright @ 1975 by Academic Press, Inc. All rights of reproduction in any form reserved.
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responses become counterconditioned to the goal-approach response. The PREE suggests that persistence learned under one disruptive or aversive situation (e.g., partial reinforcement, delay, punishment, etc.) transfers to another disruptive situation (viz., extinction). Studies have shown that transfer of persistence is not limited to the above situations. Brown and Wagner ( 1964) reported significant transfer between fear and frustration, in that subjects trained under partial reinforcement and tested under continuous punishment conditions or subjects trained under partial punishment conditions and tested in extinction showed greater persistence than control subjects trained under continuous reinforcement conditions. These results have since been replicated (Linden & Hallgren, 1973). Significant transfer has also been reported between fear of electric shock and loud noise (Terris & Wechkin, 1967). between frustration produced by partial reinforcement and partial goal blocking (Glazer & Amsel, 1970), and between frustration produced by partial reinforcement and partial delay of reinforcement and continuous delay of reinforcement (Shanab, 1971; Shanab & Cavallaro, 1973). These findings offer strong support to the commonality hypothesis of persistence effects (Wagner. 1969; Amsel, 1972). By assuming that frustration and fear have similar underlying mechanisms, the commonality hypothesis can reasonably explain the obtained transfer between responses learned under either frustration or fear-producing conditions. Specifically, persistence is mediated by the conditioned frustration (rF - sF) and the condition punishment or fear (r, - sp) mechanisms. Initially, the internal stimuli associated with the frustration and fear responses (sF and sp) evoke competing responses but eventually become counterconditioned to the ongoing goal-approach response. A simple implication of the commonality hypothesis is that various frustration-producing operations are governed by the same underlying mechanism. Thus, the conditioned frustration (rr - sF), or persistence, mechanism has been used to account for the PREE following partial reinforcement or partial delay as well as for transfer between nonreward and either delay or blocking of reward (Amsel, 1972; Shanab, 197 1). The two experiments reported here were designed to test further implications of this hypothesis. EXPERIMENT
I
Ebiperiment I was performed to test the hypothesis that rats having prior experience with a downshift in reward magnitude would persist longer than control rats when all rats receive large reward after some delay interval. Specifically, two large-rewarded groups and one smallrewarded group were run initially. Then one large-rewarded group was shifted to small reward in an effort to obtain a negative contrast effect
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(NCE) while the other continued to receive the same large reward. The rats were then tested for persistence to continuous delay. During the test phase, all rats received large reward after a 15set delay interval. According to frustration theory, all rats should experience frustration during this phase. Therefore, those rats which had already learned persistence during the downshift phase would persist longer than either the nonshifted large-reward or small-reward rats. However, the same objection raised earlier by D’Amato (1969) concerning the Brown and Wagner (1964) results is applicable to the present study. The predicted outcome could be attributed not only to prior experience with frustration but to a possible positive contrast effect (PCE) based on a shift from small to large reward. Therefore, the present experiment included a control phase which preceded the test phase, in which each rat received large immediate reward on each trial. Thus, as Linden and Hallgren (1973) suggested, any PCE would be observed and allowed to run its course before the test phase for persistence would be started. Method Design. The experiment consisted of four phases. In Phase 1, the rats received either large or small reward without delay. In Phase 2, half of the large rewarded rats continued to receive large reward (Group LL) while the other half (Group LS) was shifted to the same small reward received by the small rewarded rats (Group SS). All rats received large immediate reward in Phase 3, but in Phase 4 they received the same large reward after a 15set delay interval. Subjects. Thirty-three naive male albino rats of the Sprague-Dawley strain were used. The rats were approximately 60 days old when received from the Simonson Laboratories, Gilroy, CA. Apparatus. A 1.5-m runway made of unpainted redwood was used. The runway was covered with Plexiglas and was 23 cm high and 10 cm wide throughout. The startbox was I8 cm long and 17 cm wide. The goalbox was L-shaped. The initial section of the goalbox was 30.5 cm long and 15 cm wide. At right angles to this section was a 16 X 16 cm section in which the foodcup was placed. This prevented the rat from making any visual discrimination as to whether or not the foodcup was baited. Four sets of photocells were installed in the runway. Interruption of any of the four photobeams started and/or stopped any one of the three electric timers that measured start, run, and goal times. The first, second, third, and fourth photocells were located 6.5, 2 1.5, 103, and 115 cm from the startbox, respectively. The start- and goalboxes were separated by two guillotine doors. Procedure. Upon receipt from the supplier, the rats were placed in individual cages and had free access to food and water for thirty days. During
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this period, the rats were first weighed and then handled for 2 min a day. Thereafter all rats were given restricted food rations (approximately IO g per rat) and maintained at about 80% of their free-feeding weight, which level was reached by all rats within 14 days. Water was available freely throughout the experiment. Proper adjustment was made for food eaten in the experimental situation. Each rat was given its daily ration at least 30 min after its last daily trial. Throughout all phases of the experiment, the rats received three trials per day and were run in squads of three so as to maintain a short intertrial interval (IT1 = 3-5 min). To control for any visual cues the reinforcer was placed in the L-shaped section throughout the experiment. Pretraining started as soon as all rats reached their 80% level and consisted of allowing each rat to explore the unbaited runway for 90 set on each of three days. The equipment was turned off during the first day of exploration but was turned on during the second day in order to familiarize the rats with the different noises which would be present during regular training. On the third day of exploration, the rat’s first running times were recorded in an attempt to obtain an approximate operant level for each rat. In Phase 1, the rats were randomly assigned to two main groups. One group of 22 rats received large reward (20 45mg pellets) whereas the other group of 11 rats received small reward (two 45mg pellets). This phase lasted 48 trials. In Phase 2, the rats in the large-rewarded group were subdivided randomly into two equal groups. One subgroup (Group LL) continued to receive large reward (20 pellets) while the other (Group LS) received small reward (two pellets). The control rats (Group SS) continued to receive small reward (two pellets). This phase lasted 2 1 trials. Following stable performance in Phase 2, all rats were given large immediate reward for 21 trials (Phase 3). Finally, in Phase 4, all rats received large reward following a 15set delay interval. The rats received 27 such trials in this phase. On these trials, they were detained in the terminal section of the runway for 15 sec. following which they were allowed to enter the Lshaped section and receive the reinforcer which had just been placed. Results All analyses are based on total running speed which was obtained by multiplying the reciprocal of the sum of the start, run, and goal times by the total distance (1.27 m) traversed by each rat. Phase I. A one-way analysis of variance test was performed on the last three blocks using the downshifted group as a dummy factor. There was no significant main effect (F(2,30) < 1) . Phase 2. As Fig. 1 shows, the large rewarded group showed a marked
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decrement in performance when first shifted to small reward. This decrement was, however, overcome by the fifteenth trial. Two separate analyses of variance were performed to verify the visual analysis. The results of the analysis of variance test over the first 12 trials yielded significant main effects (F(2,30) = 10.85, p < .OOl). Individual comparisons showed that Group SS ran significantly faster than Group LS reflecting a reliable NCE (F( 1,30) = 13.72, p < .OOl). The difference between Groups LL and SS was not significant (F ( 1,30) < 1) . On the other hand, Group LL ran significantly faster than Group LS (F( 1,30) = 18.53, p < .OOl). An analysis of variance performed on the last three blocks yielded nonsignificant results (F(2,30) < 1). The same test performed on the last block yielded similar results (F(2,30) < 1). Phase 3. Figure 1 shows that when all subjects were immediately reinforced on each trial during this phase, Group LS ran consistently faster than Group LL, reflecting a possible positive contrast effect (PCE). The statistical analysis, however, did not confirm this graphical effect. Separate analyses of variance were done on each block, each yielding nonsignificant results. The results of the last block of this phase is typical (F(2,30) < 1). Similarly, the results of an analysis of variance with repeated measures performed on Blocks 2-7 yielded nonsignificant effects (F(2,30) = 1.80, p > .05 for treatment; t;(5,150) < 1 for blocks, and F( 10,150) < 1 for the interaction of blocks and treatment). The latter two findings indicate that the performance of each group was stable over almost all of Phase 3. Phase 4. As can be seen in Fig. 1, when all rats were delayed in Phase 4, their speeds dropped accordingly. However, Group LS ran faster than Group LL during the initial part of the phase. The performance of the different groups converged by Block 4 and showed a slight recovery
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thereafter. An analysis of variance with repeated measures over Blocks l-4 yielded a significant main effect (F(2,30) = 6.08, 17 < .Ol). The blockseffectwashighlysignificant (F(3,90) = 43.53,~ < .OOl). However. the interaction of the two variables was not significant (F(6,90) = .94. p > .OS). Individual comparisons showed that Group LS ran significantly faster than both Groups LL and SS (Fs( 1,30) = 10.82 and 7.31, ps -=c.005 and .025, respectively). However, the results of an analysis of variance test on Block 4 were not significant (F(2,30) < 1). On the other hand, separate analyses of variance significant (F(2,30) < 1). On the other hand, separate analyses of variance were performed on each one of the first three blocks of this phase. The first trial of the first block was excluded from the analysis on the grounds that it could be considered a regular trial in Phase 3. The results of all three tests were significant (F(2,30) = 3.74, p < .05 for the first block, F(2,30) = 7.83, p < .Ol for the second block, and F(2.30) = 3.45, p < .05 for the third block). Finally, Blocks 4-9 were subjected to an analysis of variance test which yielded nonsignificant results F( 2.30) < 1. EXPERIMENT
11
Experiment II is the complement of Experiment 1. Using the same reasoning employed earlier, the commonality hypothesis leads to the prediction that rats with prior experience with delay of reinforcement would show greater persistence when downshifted in reward magnitude than control rats not having had experience with delay. Method Design. In Phase 1, 22 randomly chosen rats received immediate large reward while a second random group of 11 rats received immediate small reward. In Phase 2, a random half of the large-rewarded Ss received their reinforcer after a 15-set delay interval (L,) while the other half continued to receive their reinforcer without delay (LND). The small rewarded rats also received immediate reinforcement (S,,). In Phase 3, delay was removed and all three groups received their respective rewards immediately. All rats in Phase 4 received small immediate reward. The third phase was intended to control for any positive contrast effects that might occur as a result of shifting rats from delay to nondelay, thus ruling out the possibility that previously delayed rats persist longer than nondelayed rats during a downshift in reward magnitude merely because the delayed rats experience positive contrast when shifted to no delay. Subjects. The rats were 33 naive male albino rats of the SpragueDawley strain and were approximately 60 days old upon arrival from the supplier. Apparatus. The apparatus used was the same as that used in Experiment I.
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Procedure. The same general procedure concerning handling, deprivation, number of trials per day, ITI, etc., which was used in Experiment I was also used in this experiment. The magnitude of reward was also the same (either twenty 45mg or two 45mg pellets), as was the delay interval (15 set). Resu Its
All analyses are based on total speeds. Phase I. An analysis of variance with repeated measures performed on the last three blocks yielded nonsignificant effects. The delayed group was included as a dummy factor. The main effect of magnitude was not significant (F(2,30) = 1.98, p > .OS). Neither the blocks nor the magnitude by blocks interaction effects were significant (F(2,60) < 1, and F(4,60) < 1, respectively) indicating that all subjects had reached a stable and comparable level by the end of the phase. Phase 2. As Fig. 2 indicates, subjects in Group L, showed a marked decrement in performance when first shifted to delay and continued to perform at a greatly depressed speed level throughout all 24 trials of the phase. This is supported by the results of several analysis of variance tests performed on the mean speeds over Block 2 alone, Blocks 1-8, Blocks 2-8, Blocks 6-8, and Block 8 alone. All tests showed significant main effects. The results of the analysis of the first and last blocks, for example, yielded the following: Fs(2,30) = 4.77 and 22.77, ps < .05 and <.OOl for Block 1 and Block 8, respectively. Individual comparisons showed that rats in Group S,, as well as those in Group L,, ran significantly faster than Ss in Group L,(Fs(l,30) = 21.64 and 43.54, both ps < .OOl). The analyses of variance on the other blocks yielded F values that were significant at the .OOl level or better. Phase 3. When delay was removed, the performance of Group L, showed a gradual recovery and eventually reached the level of the 1.25
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nondelayed groups. An analysis of variance test performed on the last three blocks yielded a nonsignificant main effect (F(2,30) = I. 16, p > .05). The same test done on the last block of this phase showed similar results (F(2,30) = 1.80, p > .OS). Phase 4. Figure 2 shows that the shift to small reward resulted in different performance-decrement rates for Groups L,, and L,. The rats in Group L, appear initially to have decreased their speeds less rapidly than those in Group L,,. This conclusion is supported by the results of a repeated-measures analysis of variance test performed on the first four blocks. The treatment effect was highly significant (F(2,30) = 1 I .39, p < .OOl). Both the blocks and the blocks by treatment effects were significant (F(3,90) = 13.94, p < .OOl and (F(6,90) =4.53, p < .OOl. respectively). The latter supports the graphical conclusion that the observed performance decrement was dependent upon the prior treatment received by the rat. Individual comparisons showed that both Groups L,, and L, ran significantly slower than Group S,,(P( 1,30) = 22.70, p < .OOl, and F(1,30) = 5.88, p < .OS, respectively). Moreover, Group L, ran significantly faster than Group L,, (F( 1,30) = 5.47, p < .05). As Fig. 2 shows, the difference in performance decrement between Groups L,, and L, disappeared by Block 5. The results of an analysis of variance test on Blocks 5 and 6 combined yielded a significant main effect (F(2,30) = 7.53, p < .Ol). Individual comparisons showed that both Groups L,, and L,, ran significantly slower than Group S,,(Fs( 1,30) = 12.53 and 9.98, both ps < .OOl, respectively). No significant difference was detected between Groups L,, and L,, (F( I ,30) < 1) . Finally, as Fig. 2 indicates, all groups converged to a common level by the end of the phase. This conclusion is supported by the results of two analyses of variance. One test which was performed on the last three blocks yielded a nonsignificant main effect (F(2.30) = 3.21, p > .05, whereas the other test performed on the last block yielded similar results (F(2,30) = 1.50, p > .05). Discussion
In both experiments, the obtained negative contrast was short-lived. This is in agreement with the findings of several studies (viz. Spear & Spitzner, 1968; Capaldi, 1972; Capaldi & Singh, 1973). On the other hand, both experiments showed that delay produced marked and lasting decrements in performance. To be sure, the delayed subjects showed a slight recovery, but their performance stabilized at a significantly lower level than the nondelayed control subjects. One obvious implication of this asymmetry is that the two operations of delaying reward and reducing reward magnitude have different behavioral consequences: this probably accounts for the differential transfer
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effects obtained in the two studies. A second and probably more important implication is that the rather permanent decremental effects of delay could account for the relative permanence of the positive contrast effect obtained in studies which use delay as a procedure for ceiling effects (Mellgren, 1971; Mellgren, Seybert, Wrather & Dyck, 1973; Shanab. Birnbaum & Cavallaro, 1974). Both experiments showed that persistence learned under one frustration-producing condition transfers to a different frustration-producing condition. Thus, those rats which experienced a downshift in magnitude of reward showed greater persistence to delay of reward than those that did not have prior experience with a downshift in magnitude of reward (Experiment I). Similarly, rats with a history of delay of reward showed greater persistence to a downshift in reward magnitude than those that did not have such a history (Experiment II). Both findings confirm in general the earlier predictions based on Amsel’s theory of persistence (1972). Although the present experiments were designed to test certain implications of Amsel’s persistence theory, the results nevertheless are amenable to Capaldi’s (1972) latest interpretation of negative contrast effects. Earlier, Capaldi (1967) had proposed that the NCE is a function of generalization decrement experienced by the downshifted rats relative to the nonshifted rats. The NCE would not be permanent, because the rats would soon adjust to the absolute characteristics of the reward magnitude so that the aftereffects of the small reward (SRS) would become conditioned to the instrumental response, and the rat would eventually run at the same level as the control group. Recently, Capaldi (1972) attributed the NCE to four sources of generalization decrement associated with four unconditioned stimuli. Two of these stimuli, namely frustration stimuli (SF) and stimuli specific to the small reward magnitude (SRs) are ITIdependent in the sense that the intensity of such stimuli diminishes as the IT1 increases. The two other stimuli, S and S’“, are also associated with frustration and reward magnitude respectively but are not dependent on the ITI. Thus. according to this notion, only two sources of generalization decrement (Sf and Srs) contribute to NCE when trials are spaced but four such sources are involved when trials are massed (SF, SRS, Sf, and F). The obvious deduction, for which Capaldi (1972) provided ample evidence, is that the NCE would be larger following massed than spaced training. A second deduction leads to the prediction that little or no NCE would be expected in rats whose instrumental response had already been conditioned to one or more of these stimuli. In two separate studies (Capaldi & Lynch, 1967; Capaldi, 1972), it was found that while rats shifted from large to small reward showed a reliable NCE, those receiving the same treatment but with prior training with small reward showed no NCE. Ac-
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cording to Capaldi’s theory, the former group, called the nontransfer shift group, suffers four sources of generalization decrement (SF. Sf, SRS, and Srs), while for the latter, called the transfer shift group, two sources of generalization decrement (S” and Sf) presumably contribute to the NCE. Capaldi’s theory can thus account for the present findings by assuming that the stimulus aftereffects of frustration resulting from a downshift in reward magnitude are similar to those produced by delay. Thus for Experiment I this assumption implies that rats previously experiencing a reduction in reward magnitude would, when introduced to delay, experience a transfer shift (Group LS) while those introduced to the delay variable following a history of continuous immediate reward experience a nontransfer shift (Group LL). Similarly, in Experiment II, for those rats with prior experience with delay of reward a reduction in reward magnitude would constitute a transfer shift (Group L,,), but for rats that receive a downshift in reward magnitude without any prior experience with delay such an experience would constitute a nontransfer shift (Group L,,,). Thus the nontransfer-shift rats (Groups LL and L,,) should show less persistence during either delay or downshift in reward magnitude than transfer-shift rats (Groups LS and L,), which was the case in the present experiments. The lack of permanence of the persistence effects is in agreement with one major assumption of Capaldi’s theory, namely, that performance is a function of the absolute current characteristics of the reinforcement conditions. Thus, the performance of all rats regardless of their prior reinforcement history, should eventually come under the control of the current reinforcement conditions, thus according for the shortterm effects of the persistence effects in the present research. Finally, it should be noted that a closer examination of the results obtained in Phase 4 of both experiments reveals that the transfer effects obtained probably reflect partial transfer. This point can be made more clearly if the results of the second experiment are discussed first. In the latter experiment, rats with a prior history of delay also showed a negative contrast effect, which was of a lesser magnitude than the one observed in the nondelayed control rats. A full transfer effect would require that a NCE be observed in the control group only. Nonetheless, the significant transfer effects are consistent with the earlier predictions based on Amsel’s theory of persistence (1972). It was not expedient in Experiment I to run a second control group which received continuous delay all the time. Thus, although rats with a prior history of NCE were found to resist continuous delay longer than control rats not having had such experience (which confirms the hypothesis being tested), it is not known how the experimental rats would have performed relative to a second control group such as the one just described. In the absence of such a control
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group, it is probably more accurate to refer to the results of Experiment I as reflecting partial rather than full transfer. There are provisions in both Amsel’s and Capaldi’s theories to account for the partial transfer of persistence effects. According to Amsel, partial transfer would be attributed to similar but overlapping systems of persistence. In Capaldi’s recent terms, this effect could be accounted for by assuming that only frustrative stimuli (SF and Sf) are involved in the transfer between delay of reward and reductions in magnitude of reward. The specific stimuli associated with small reward (SRS and Srs) apparently do not contribute appreciably to the transfer of persistence between delay (SD and Sd) and downshifts in reward magnitude. In conclusion, it seems appropriate to point out the striking convergence of both the frustration and sequential theories towards a common explanation of behavioral phenomena (cf., Shanab & Birnbaum, 1974). With the admission of frustration stimuli, the sequential theory of Capaldi can now account for a variety of frustration-related phenomena that heretofore were more directly explicable in terms of frustration theory. REFERENCES Amsel,
A. Behavioral habituation, counterconditioning, and persistence. In A. Black and W. K. Prokasy (Eds.). Classical Conditioning II, New York: Appleton-Century-Crofts. 1972. Pp. 409-425. Banks, R. K. Persistence to continuous punishment following intermittent punishment training. Journal of Experimental Psychology. 1966, 71, 373-377. Capaldi, E. D., & Singh, R. Percentage body weight and the successive negative contrast effect. Learning & Motivation, 1973, 4, 405-416. Capaldi, E. J. A sequential hypothesis of instrumental learning. In K. Spence and J. T. Spence (Eds.), The psychology of learning and motivation: Advances in research and theory. Vol. 1. New York: Academic Press. 1967. Pp. 67-156. Capaldi, E. J. Successive negative contrast effect: Intertrial interval, type of shift, and four sources of generalization decrement. Journal of Experimental Psychology, 1972, 96, 433-438. Capaldi, E. J., & Lynch, D. Repeated shifts in reward magnitude: Evidence of an associational and absolute (noncontexual) interpretation. Journal of Experimental Psychology, 1967,75, 226-235. D’Amato, M. R. Instrumental conditioning. In M. H. Marx (Ed.) Learning Processes. Toronto: Macmillan, 1969. Pp. 35-l 18. Donin, J. A., Surridge, C. T., & Amsel, A. Extinction following partial delay of reward with immediate continuous reward interpolated at 24-hour intertrial intervals. Journal of Experimental Psychology, 1967, 1, 50-53. Dyck, D. G., Mellgren, R. L., & Nation, J. R. Punishment of appetitively reinforced instrumental behavior: Factors affecting response persistence. Journal of Experimental Psychology, 1974, 102, 125-132. Fallon, D. Resistence to extinction following learning with punishment of reinforced and nonreinforced licking. Jorlrnal of Experimental Psychology, 1968,76, 550-557.
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Glazer. H.. & Amsel. A. Transfer of persistence effects from frustration produced h! blocking to frustration produced by nonreinforcement. Prvc~lr~~rromic~ S~~i~~nc~e. I Y70. 18. 311-312. Linden. D. R.. & Hallgren, S. 0. Transfer of approach responding between punishment and frustrative nonreward sustained through continuous reinforcement. Lc,rrrrrirrv (in