Journal of Comparative and Physiological Psycholog, 1975, Vol.^88, No. 1, 104-109
DISCRIMINABILITY AND THE CONTRAFREELOADING PHENOMENON1 GEORGE T. TAYLOR2 State University oj New York College at Potsdam According to previous reports of the "contrafreeloading phenomenon," animals will work for a reward, and sometimes work quite hard, in the presence of the same reward available freely. With rats as the subjects two experiments are presented which suggest that the contrafreeloading data are explainable with a basic learning principle, discriminability and its accompanying response decrement. For some animals the change in stimulus conditions with introduction of free water was made more highly discriminable by a change in earned reinforcement conditions. The other animals remained on the same earned reinforcement conditions under which all the animals had been trained. The results demonstrated that the discriminability between the conditions of working and freeloading is a most important factor contributing to the continued responding in the presence of free rewards.
Several authors (Carder & Berkowitz, eat the food. However, a basic assumption 1970; Neuringer, 1969, 1970; Singh, 1970) of most learning theories, and incentive have recently reported a "contrafreeloading theories in particular (Logan, 1960; Logan & phenomenon." Animals continued to respond Wagner, 1965; Tolman, 1955), is that anifor food in a simple operant setting even after mals will demonstiate a selective preference free food was introduced. In fact, under for the least effortful response in an environsome conditions, the animals actually pre- ment provided that the various response ferred the earned food. These data have a alternatives differ only with respect to the wide range of implications for learning, as effort variable. Thus, for example, an animal well as behavior theories in general. will prefer a less effortful response provided In 1963, Jensen taught a large number of that it has comparable experiences with that rats to bar press for food on continuous alternative, and the response provides the reinforcement (CRF) and then introduced a same payoff as the more effortful one. dish of free food in the end of the box oppoAlthough several of the previous authors site to the bar. Results were recorded only (Neuringer, 1969; Singh, 1970) suggest that on 1 test day, but with sufficient initial bar- the contrafreeloading data are unexplainable press training (over 640 responses), the rats and certainly unpredictable from a classic preferred the earned food. More recently, learning viewpoint (e.g., Hull, 1943), there Carder and Berkowitz (1970) employed a is one characteristic of the earlier studies similar setting and generated the same data. that may have contributed to continued Finally, Singh (1970) found that in quite bar pressing in the presence of free rewards. divergent experimental situations, both Consider three reference experiments. Carder children and rats chose to work rather than and Berkowitz (1970) bar-press-trained rats to freeload. on continuous reinforcement, then introThe apparent implication of these studies duced free food. As long as the schedule of is that "work" holds intrinsic appeal for an earned reinforcement remained CRF or was organism (e.g., Jensen, 1963), and it may changed only slightly, to fixed ratio (FR) 2, prefer to respond and eat rather than just the animals preferred to work. However, 1 This research was supported in part by Grant when the reinforcement schedule was 1 R03 MH-25300-01 from the National Institute switched to FR 10, the animals discontinued of Mental Health. bar pressing and became freeloaders. The 2 Requests for reprints should be sent to George authors' conclusion was that rats prefer T. Taylor, Department of Psychology, State University of New York College at Potsdam, Potsdam, earned food to free food as "long as the work demands are not too high." New York 13676. 104
DISCRIMINABILITY AND CONTRAFREELOADING
Neuringer (1970), however, demonstrated that animals would work quite hard, up to 70 responses per reinforcement, in the presence of free food if the animals were originally trained on the longer schedule. Finally, the present investigator (G. T. Taylor, unpublished manuscript, 1973) utilized a setting in which 2 highly discriminable tones signaled and distinguished between the earned-food condition and the free-food condition. The results were that the animals exhibited greatly reduced levels of earned food responding relative to those that had been previously noted. An analysis of these data suggests that one must consider that food (or water) is a stimulus, an SD, in the presence of which the animal had previously been reinforced for bar pressing. Furthermore, the less the change in the stimulus setting, the slower the animal "realizes" the conditions of reinforcement have changed (e.g., Capaldi, 1967). Thus, the less the stimulus change from the purely work condition to the choice between working and freeloading, the slower the retardation of the bar-press response, i.e., the less the response decrement. An overwhelming number of the previous studies (Davidson, 1971; Jensen, 1963; Stolz & Lott, 1964; Tarte & Snyder, 1972) employed a relatively subtle change when the free food was introduced. However, when the change was made more distinctive, the animals greatly reduced the numbers of bar-press responses in the presence of free food. For example, Carder and Berkowitz (1970) found that when the conditions of work were made too different from the original CRF training condition, i.e., a shift to longer FR schedules, the animals stopped bar pressing altogether. Neuringer's (1970) pigeons, however, made a large number of responses for food in the presence of free food, for that was the condition under which they had been trained. Two experiments are reported here in which the discrimination proposal is put to a direct empirical test. For some animals the introduction of the free-water condition was made more highly discriminable by a change in earned reinforcement conditions. The other rats remained on the same earned
105
reinforcement conditions under which all the animals had been trained. EXPERIMENT 1 Method Subjects. Twelve Holtzman male albino rats were used as subjects. The experimentally naive animals, approximately 100 days old at the beginning of experimentation, were housed individually with food freely available. The subjects received 25 ml. of water, minus the amount consumed in the experimental environment, immediately following each daily session. Apparatus. The experimental chambers consisted of 3 identical standard operant boxes, 21.6 X 22.9 X 21.6 em. The water delivery was by a dipper, located 7 cm. to the left of the bar, which delivered .01 cc of liquid. The floors were comprised of .43-cm. stainless steel rods spaced 1.91 cm. apart. The boxes were housed in soundproof cubicles. Finally, the free water was introduced in a small plastic dish, 6 cm. in diameter and 4 cm. deep. Procedure. The rats were initially gentled and adapted to a 23-hr, water deprivation schedule for 7 days prior to the beginning of experimentation. Animals were then trained in an operant box to bar press for .01 cc water on specific work terms, variable interval (VI) 20 sec. Each of the daily experimental sessions was 30 min. Following 24 days of experience on the VI schedule, a small dish containing 40 ml. of water was introduced in the end of the box opposite to the bar and the bar was covered. The rats were then allowed to drink from the dish for 1 day. The following day free-choice testing began. This procedure is one initially employed by Jensen (1963) and subsequently employed most frequently in the contrafreeloading literature (e.g., Carder, 1972; Tarte & Snyder, 1972). During the free-choice trials, free water was present, the bar was uncovered, and the subjects were given a choice between bar pressing and freeloading. One group in the experiment was maintained on the original work terms, i.e., the VI 20-sec. schedule, in the presence of free water. A second group was changed to more difficult work terms, that is, VI 30 sec. A third group was switched instead to less difficult work terms, VI 10 sec. The animals were given a total of 10 daily experimental sessions in the free-choice condition. Each day the total amount of water consumed from the free dish and the number of bar presses for water was recorded.
Results The general findings were that the animals in all VI conditions exhibited a vast preference for free water. In fact, every animal earned less than 1 % of its water on every
106
GEORGE T. TAYLOR
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the VI 20-sec. group drank less free water than the VI 10- or VI 30-sec. groups (Ms = 17.80 ml., 21.55 ml., and 22.30 ml., respectively). An analysis of variance with amount of free water consumed over the first 5 days was significant (F = 26.26, df = 2/9, p < .05). Subsequent a posteriori comparisons of mean performance differences, again with the Scheffe' procedure (.01 confidence level), demonstrated that the VI 20-sec. subjects did, in fact, drink less free water than the other animals.
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choice day. As a result, the data of greatest interest became the differences in number of bar-press responses by the 3 groups. Prior to the change in experimental conditions and the addition of free water, the animals' levels of bar pressing did not differ (F < 1). Figure 1 represents the average number of bar presses on each of the VI schedules following introduction of the free water. Although the number of responses are minimal, there is the suggestion that the VI 20-sec. animals made more responses than either the VI 10- or the VI 30-sec. group. An analysis of variance with total number of responses during the choice phase yielded a significant value (F = 21.23, df = 2/9, p < .05). A posteriori comparisons examining mean performance differences by the SchefK method (.01 confidence level) revealed that the VI 20-sec. animals made more bar-press responses than the VI 10- or VI 30-sec. rats. Furthermore, the results from the amount of water consumed suggested that initially
EXPERIMENT 2 The data of the initial experiment certainly lend support to the proposal that discriminability plays a key role in the contrafreeloading phenomenon. However, a second experiment was performed to examine the possibility that the results generated in Experiment 1 were peculiar to the VI schedules employed. 1'ixed-ratio schedules were chosen since a previous study (Davidson, 1971) had suggested an FR schedule to be particularly potent in producing a large number of bar-press responses in the presence of free rewards. The large number of responses were of particular interest since the animals made relatively few bar-press responses under the VI schedules after the free water was introduced. Method Subjects. Nine Holtzman male albino rats were used in the second experiment. The experimentally naive animals were 90-120 days old at the beginning of experimentation. Following each daily 30-min. experimental session, the animals were returned to their individual home cages and were given 25 ml. of water, minus the amount consumed in the session. Finally, ad-lib food was available throughout the experiment. Apparatus. The same apparatus used in the first experiment was also used in Experiment 2. Procedure. The general procedure was identical to that of the first experiment; however, FR schedules were used to define the various work terms. Following pretraining, all animals were trained to bar press for water on FR 10. Following 20 days experience on the FR 10, free water was introduced for 1 day in the end of the box opposite to the bar, and the bar was covered. The following day free water was again introduced, the bar was uncovered, and the animals were given a choice between bar pressing and freeloading. One group of animals remained on the original work terms in the presence of the free
DISCRIMINABILITY AND CONTRAFREELOADING water. The second group was switched to greater work terms and a third group was changed to lesser work terms, FR 15 and FR 5, respectively. Again, the animals were given 10 daily free-choice sessions of 30 min. each.
FR5-
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Results The animals exhibited higher levels of bar pressing in the presence of free water under the fixed ratio schedules than the variable interval schedules of Experiment 1. However, the rats still demonstrated a vast preference for free water, consistently over 95%. The average number of bar-press responses are presented in Figure 2. The animals' responding did not differ in the training stage before the change in experimental conditions (F < 1). However, examination of the second graph, in agreement with the findings of Experiment 1, suggests that the reinforcement condition, which was not changed with the introduction of free water, produced the greatest number of bar-press responses. An analysis of variance investigating the total number of bar presses during the choice phase confirmed a statistically reliable effect (F = 29.20, df = 2/6, p < .05). The Scheffe" method (.01 confidence level) was applied a posteriori examining mean response differences. The results demonstrated that the FR 10 subjects made significantly more responses than the FR 5 or FR 15 animals. Finally, and in contrast to the first experiment, the animals under the FR schedules did not differ with respect to amount of free water consumed (F < 1). DISCUSSION The findings of the 2 experiments imply that an important variable in the contrafreeloading phenomenon is the discriminability of the change to a choice between working and freeloading. The prediction from the discriminability proposal is that the animals experiencing a change in work terms, either to greater or to lesser demands, will exhibit increased levels of freeloading relative to animals maintained on the originally trained conditions. Thus, the work terms which signal, and continue signaling for the duration of the experiment, that the experimental conditions have changed from
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CHOICE
BLOCKS OF TWO DAYS
FIGURE 2. The average numbers of bar-press responses under the fixed-ratio (FR) schedules prior to and after the introduction of free water.
the original training setting will produce the greatest amounts of freeloading. This effect should be independent of whether the change is to greater or lesser work terms. Those are precisely the data generated in the present setting. The animals remaining on the originally trained work terms, i.e., those not signaled of the change to a choice between earned and free water, continued to work in the presence of free water at a higher rate and for longer durations than the animals that were signaled of the change. These data suggest that an animal experiencing a change in work demands, regardless of whether to more difficult or less difficult terms via a change to the shorter or longer schedules, will demonstrate an increased level of freeloading relative to an animal maintained on the originally trained schedule. The results of the present experiments bear upon a most basic question in learning
108
GEORGE T. TAYLOR
theory. That is, do animals in fact prefer the least effortful path to a goal? The contrafreeloading findings of a large number of studies (Neuringer, 1969, 1970; Singh, 1970) suggest quite the opposite. Animals will work for food or water, and sometimes will work quite hard, in the presence of the same reward freely available. The implication of the contrafreeloading phenomenon is that the learning theorist, and incentive theorist in particular, must invoke one or more additional assumptions to more realistically represent animal learning. For example, Jensen (1963) has suggested that bar pressing holds "intrinsic appeal" for a rat. Other investigators (Carder & Berkowitz, 1970) have proposed that "as long as the work demands are not too high" animals will prefer to earn their rewards freely. Hnally, Singh (1972) has implied that the Protestant work ethic is as basic to the rat as to man. Yet, are there more parsimonious explanations of the contrafreeloading phenomenon? The findings of the present experiments suggest that the contrafreeloading data can be accounted for with a basic learning principle. That is, the discriminability between the conditions of working and freeloading is a most important factor contributing to the continued responding in the presence of free rewards. The typical contrafreeloading paradigm (e.g., Carder & Berkowitz, 1970) is to teach an animal over several days to bar press in an operant box. Then free food is introduced. An animal is given brief exposure to the free food and then allowed to choose between working and freeloading. Yet one must consider that stimuli within the operant box environment have become discriminative stimuli in the presence of which the animal has previously been reinforced for bar pressing. Furthermore, the less the change in the stimulus situation with the introduction of free food, the slower the animal realizes the conditions have changed (Capaldi, 1967). Thus, the less the stimulus changes from the purely work condition to the choice between working and freeloading, the slower is the retardation of the bar-press response, i.e., the less the response decrement. Several other findings in the present
setting support the discriminability notion. First, animals made considerably more barpress responses in the presence of free water under the FR schedules than under the VI schedules. Informal observation of the animals suggested that during training the FR animals were much busier in the operant box than the VI rats. The FR animals seldom left the locus of the bar and, as a result, exhibited high levels of bar pressing during training. The VI animals, however, were much more likely to wander around the box during the experimental session. When free water was introduced, it was not surprising that the VI animals had a higher probability of discovering, and rediscovering periodically, the dish of free water than the generally "hardworking" FR animals. These observations confirm and extend the earlier observation (Taylor, 1972) that the few animals that genuinely preferred to bar press when free rewards were available were those animals that started pressing immediately upon being placed into the apparatus. Moreover, those rats remained at the bar for the largest portion of the session in the apparatus. Second, the animals, at least in the first experiment, that were not cued of the change in reinforcement conditions drank less water than the signaled animals. Again, there is the suggestion that the discriminability of the new reward source is a contributor to the contrafreeloading findings. Moreover, the data of the present experiments confirm the earlier findings that the animals gradually and predictably bar press less in the presence of free rewards over time (Taylor, 1972). That is, as the animals slowly learn that there is an easier, quicker source of the reward than bar pressing, they shift to the free rewards. After a few days the animals only infrequently bar press. Therefore, these data are quite in opposition to the earlier proposal (Carder & Berkowitz, 1970) that the difficulty of earning the reward determines the degree of working in the presence of free rewards. Neither is it necessary to speculate on the intrinsic appeal of bar pressing (Jensen, 1963) or of the work ethic (Singh, 1972). Instead, the present data suggest that one factor contributing to the continued responding in the presence
DISCRIMINABILITY AND CONTEAFREELOADING of free water is the discriminability between the original work condition and the subsequent freeloading condition. Many of the previous investigations in the contrafreeloading literature (Carder, 1972; Carder & Berkowitz, 1970; Neuringer, 1969, 1970; Stolz & Lott, 1964; Tarte & Snyder, 1972; 1973) are susceptible to interpretation from the parsimonious discrimination proposal. Finally, Mitchell and his associates (Mitchell, Scott, & Williams, 1973) have recently generated data to support their interpretation of contrafreeloading from an ethological viewpoint. They suggest that rats continue to bar press and receive food at a familiar source rather than eat free food at an unfamiliar source because the animals are neophobic. The present analyses are in essential agreement with their proposal. The "fear" of the newly introduced free-food source could simply be viewed as a lack of discriminability of the change in stimulus conditions, i.e., a lack of opportunity to learn the appropriate approach and consummatory responses to the free food. In summary, the seemingly troublesome contrafreeloading findings can be explained, at least to some extent, with a basic stimulus-response learning principle, discriminability of stimulus changes and its accompanying response decrement. REFERENCES Capaldi, E. J. A sequential hypothesis of instrumental conditioning. In K. W. Spenee & J. T. Spence (Eds.), The psychology of learning and motivation. New York: Academic Press, 1967. Carder, B. Rats preference for earned in comparison with free liquid reinforcers. Psychonomic Science, 1972, 26, 25-26.
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Carder, B., & Berkowitz, K. Rats preference for earned in comparison with free food. Science, 1970, 167, 1273-1274. Davidson, A. B. Factors affecting keypress responding by rats in the presence of free food. Psychonomic Science, 1971, 24, 135-137. Hull, C. L. Principles of behavior. New York: Appleton-Century-Crofts, 1943. Jensen, G. D. Preference of bar pressing over "freeloading" as a function of number of rewarded presses. Journal of Experimental Psychology, 1963, 65, 451-454. Logan, F. A. Incentive. New Haven: Yale University Press, 1960. Logan, F. A., & Wagner, A. R. Reward and punishment. Boston: Allyn & Bacon, 1965. Mitchell, D., Scott, D. W., & Williams, K. D. Container neophobia and the rats preference for earned food. Behavioral Biology, 1973, 9, 613-624. Neuringer, A. J. Animals respond for food in the presence of free food. Science, 1969,166, 399-401. Neuringer, A. J. Many responses per food reward with free food present. Science, 1970, 168, 503504. Singh, D. Preference for bar pressing to obtain reward over freeloading in rats and children. Journal of Comparative and Physiological Psychology, 1970, 73, 320-327. Singh, D. The pied piper vs the Protestant ethic. Psychology Today, 1972, 5, 53-56. Stolz, S. B., & Lott, D. F. Establishment in rats of a persistent response producing a net loss of reinforcement. Journal of Comparative and Physiological Psychology, 1964, 57, 147-149. Tarte, R. D., & Snyder, R. L. Bar-pressing in the presence of free food as a function of food deprivation. Psychonomic Science, 1972, 26, 169-170. Tarte, R. D., & Snyder, R. L. Some sources of variation in the bar pressing versus freeloading phenomenon in rats. Journal of Comparative and Physiological Psychology, 1973, 84, 128-133. Taylor, G. T. A limitation of the contrafreeloading phenomenon. Psychonomic Science, 1972, 29, 173-174. Tolman, E. C. Principles of performance. Psycliological Review, 1955, 62, 315-326. (Received September 19, 1973)
DISCRIMINABILITY AND THE CONTRAFREELOADING PHENOMENON1 GEORGE T. TAYLOR2 State University oj New York College at Potsdam According to previous reports of the "contrafreeloading phenomenon," animals will work for a reward, and sometimes work quite hard, in the presence of the same reward available freely. With rats as the subjects two experiments are presented which suggest that the contrafreeloading data are explainable with a basic learning principle, discriminability and its accompanying response decrement. For some animals the change in stimulus conditions with introduction of free water was made more highly discriminable by a change in earned reinforcement conditions. The other animals remained on the same earned reinforcement conditions under which all the animals had been trained. The results demonstrated that the discriminability between the conditions of working and freeloading is a most important factor contributing to the continued responding in the presence of free rewards.
Several authors (Carder & Berkowitz, eat the food. However, a basic assumption 1970; Neuringer, 1969, 1970; Singh, 1970) of most learning theories, and incentive have recently reported a "contrafreeloading theories in particular (Logan, 1960; Logan & phenomenon." Animals continued to respond Wagner, 1965; Tolman, 1955), is that anifor food in a simple operant setting even after mals will demonstiate a selective preference free food was introduced. In fact, under for the least effortful response in an environsome conditions, the animals actually pre- ment provided that the various response ferred the earned food. These data have a alternatives differ only with respect to the wide range of implications for learning, as effort variable. Thus, for example, an animal well as behavior theories in general. will prefer a less effortful response provided In 1963, Jensen taught a large number of that it has comparable experiences with that rats to bar press for food on continuous alternative, and the response provides the reinforcement (CRF) and then introduced a same payoff as the more effortful one. dish of free food in the end of the box oppoAlthough several of the previous authors site to the bar. Results were recorded only (Neuringer, 1969; Singh, 1970) suggest that on 1 test day, but with sufficient initial bar- the contrafreeloading data are unexplainable press training (over 640 responses), the rats and certainly unpredictable from a classic preferred the earned food. More recently, learning viewpoint (e.g., Hull, 1943), there Carder and Berkowitz (1970) employed a is one characteristic of the earlier studies similar setting and generated the same data. that may have contributed to continued Finally, Singh (1970) found that in quite bar pressing in the presence of free rewards. divergent experimental situations, both Consider three reference experiments. Carder children and rats chose to work rather than and Berkowitz (1970) bar-press-trained rats to freeload. on continuous reinforcement, then introThe apparent implication of these studies duced free food. As long as the schedule of is that "work" holds intrinsic appeal for an earned reinforcement remained CRF or was organism (e.g., Jensen, 1963), and it may changed only slightly, to fixed ratio (FR) 2, prefer to respond and eat rather than just the animals preferred to work. However, 1 This research was supported in part by Grant when the reinforcement schedule was 1 R03 MH-25300-01 from the National Institute switched to FR 10, the animals discontinued of Mental Health. bar pressing and became freeloaders. The 2 Requests for reprints should be sent to George authors' conclusion was that rats prefer T. Taylor, Department of Psychology, State University of New York College at Potsdam, Potsdam, earned food to free food as "long as the work demands are not too high." New York 13676. 104
DISCRIMINABILITY AND CONTRAFREELOADING
Neuringer (1970), however, demonstrated that animals would work quite hard, up to 70 responses per reinforcement, in the presence of free food if the animals were originally trained on the longer schedule. Finally, the present investigator (G. T. Taylor, unpublished manuscript, 1973) utilized a setting in which 2 highly discriminable tones signaled and distinguished between the earned-food condition and the free-food condition. The results were that the animals exhibited greatly reduced levels of earned food responding relative to those that had been previously noted. An analysis of these data suggests that one must consider that food (or water) is a stimulus, an SD, in the presence of which the animal had previously been reinforced for bar pressing. Furthermore, the less the change in the stimulus setting, the slower the animal "realizes" the conditions of reinforcement have changed (e.g., Capaldi, 1967). Thus, the less the stimulus change from the purely work condition to the choice between working and freeloading, the slower the retardation of the bar-press response, i.e., the less the response decrement. An overwhelming number of the previous studies (Davidson, 1971; Jensen, 1963; Stolz & Lott, 1964; Tarte & Snyder, 1972) employed a relatively subtle change when the free food was introduced. However, when the change was made more distinctive, the animals greatly reduced the numbers of bar-press responses in the presence of free food. For example, Carder and Berkowitz (1970) found that when the conditions of work were made too different from the original CRF training condition, i.e., a shift to longer FR schedules, the animals stopped bar pressing altogether. Neuringer's (1970) pigeons, however, made a large number of responses for food in the presence of free food, for that was the condition under which they had been trained. Two experiments are reported here in which the discrimination proposal is put to a direct empirical test. For some animals the introduction of the free-water condition was made more highly discriminable by a change in earned reinforcement conditions. The other rats remained on the same earned
105
reinforcement conditions under which all the animals had been trained. EXPERIMENT 1 Method Subjects. Twelve Holtzman male albino rats were used as subjects. The experimentally naive animals, approximately 100 days old at the beginning of experimentation, were housed individually with food freely available. The subjects received 25 ml. of water, minus the amount consumed in the experimental environment, immediately following each daily session. Apparatus. The experimental chambers consisted of 3 identical standard operant boxes, 21.6 X 22.9 X 21.6 em. The water delivery was by a dipper, located 7 cm. to the left of the bar, which delivered .01 cc of liquid. The floors were comprised of .43-cm. stainless steel rods spaced 1.91 cm. apart. The boxes were housed in soundproof cubicles. Finally, the free water was introduced in a small plastic dish, 6 cm. in diameter and 4 cm. deep. Procedure. The rats were initially gentled and adapted to a 23-hr, water deprivation schedule for 7 days prior to the beginning of experimentation. Animals were then trained in an operant box to bar press for .01 cc water on specific work terms, variable interval (VI) 20 sec. Each of the daily experimental sessions was 30 min. Following 24 days of experience on the VI schedule, a small dish containing 40 ml. of water was introduced in the end of the box opposite to the bar and the bar was covered. The rats were then allowed to drink from the dish for 1 day. The following day free-choice testing began. This procedure is one initially employed by Jensen (1963) and subsequently employed most frequently in the contrafreeloading literature (e.g., Carder, 1972; Tarte & Snyder, 1972). During the free-choice trials, free water was present, the bar was uncovered, and the subjects were given a choice between bar pressing and freeloading. One group in the experiment was maintained on the original work terms, i.e., the VI 20-sec. schedule, in the presence of free water. A second group was changed to more difficult work terms, that is, VI 30 sec. A third group was switched instead to less difficult work terms, VI 10 sec. The animals were given a total of 10 daily experimental sessions in the free-choice condition. Each day the total amount of water consumed from the free dish and the number of bar presses for water was recorded.
Results The general findings were that the animals in all VI conditions exhibited a vast preference for free water. In fact, every animal earned less than 1 % of its water on every
106
GEORGE T. TAYLOR
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the VI 20-sec. group drank less free water than the VI 10- or VI 30-sec. groups (Ms = 17.80 ml., 21.55 ml., and 22.30 ml., respectively). An analysis of variance with amount of free water consumed over the first 5 days was significant (F = 26.26, df = 2/9, p < .05). Subsequent a posteriori comparisons of mean performance differences, again with the Scheffe' procedure (.01 confidence level), demonstrated that the VI 20-sec. subjects did, in fact, drink less free water than the other animals.
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choice day. As a result, the data of greatest interest became the differences in number of bar-press responses by the 3 groups. Prior to the change in experimental conditions and the addition of free water, the animals' levels of bar pressing did not differ (F < 1). Figure 1 represents the average number of bar presses on each of the VI schedules following introduction of the free water. Although the number of responses are minimal, there is the suggestion that the VI 20-sec. animals made more responses than either the VI 10- or the VI 30-sec. group. An analysis of variance with total number of responses during the choice phase yielded a significant value (F = 21.23, df = 2/9, p < .05). A posteriori comparisons examining mean performance differences by the SchefK method (.01 confidence level) revealed that the VI 20-sec. animals made more bar-press responses than the VI 10- or VI 30-sec. rats. Furthermore, the results from the amount of water consumed suggested that initially
EXPERIMENT 2 The data of the initial experiment certainly lend support to the proposal that discriminability plays a key role in the contrafreeloading phenomenon. However, a second experiment was performed to examine the possibility that the results generated in Experiment 1 were peculiar to the VI schedules employed. 1'ixed-ratio schedules were chosen since a previous study (Davidson, 1971) had suggested an FR schedule to be particularly potent in producing a large number of bar-press responses in the presence of free rewards. The large number of responses were of particular interest since the animals made relatively few bar-press responses under the VI schedules after the free water was introduced. Method Subjects. Nine Holtzman male albino rats were used in the second experiment. The experimentally naive animals were 90-120 days old at the beginning of experimentation. Following each daily 30-min. experimental session, the animals were returned to their individual home cages and were given 25 ml. of water, minus the amount consumed in the session. Finally, ad-lib food was available throughout the experiment. Apparatus. The same apparatus used in the first experiment was also used in Experiment 2. Procedure. The general procedure was identical to that of the first experiment; however, FR schedules were used to define the various work terms. Following pretraining, all animals were trained to bar press for water on FR 10. Following 20 days experience on the FR 10, free water was introduced for 1 day in the end of the box opposite to the bar, and the bar was covered. The following day free water was again introduced, the bar was uncovered, and the animals were given a choice between bar pressing and freeloading. One group of animals remained on the original work terms in the presence of the free
DISCRIMINABILITY AND CONTRAFREELOADING water. The second group was switched to greater work terms and a third group was changed to lesser work terms, FR 15 and FR 5, respectively. Again, the animals were given 10 daily free-choice sessions of 30 min. each.
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107
FR15'
Results The animals exhibited higher levels of bar pressing in the presence of free water under the fixed ratio schedules than the variable interval schedules of Experiment 1. However, the rats still demonstrated a vast preference for free water, consistently over 95%. The average number of bar-press responses are presented in Figure 2. The animals' responding did not differ in the training stage before the change in experimental conditions (F < 1). However, examination of the second graph, in agreement with the findings of Experiment 1, suggests that the reinforcement condition, which was not changed with the introduction of free water, produced the greatest number of bar-press responses. An analysis of variance investigating the total number of bar presses during the choice phase confirmed a statistically reliable effect (F = 29.20, df = 2/6, p < .05). The Scheffe" method (.01 confidence level) was applied a posteriori examining mean response differences. The results demonstrated that the FR 10 subjects made significantly more responses than the FR 5 or FR 15 animals. Finally, and in contrast to the first experiment, the animals under the FR schedules did not differ with respect to amount of free water consumed (F < 1). DISCUSSION The findings of the 2 experiments imply that an important variable in the contrafreeloading phenomenon is the discriminability of the change to a choice between working and freeloading. The prediction from the discriminability proposal is that the animals experiencing a change in work terms, either to greater or to lesser demands, will exhibit increased levels of freeloading relative to animals maintained on the originally trained conditions. Thus, the work terms which signal, and continue signaling for the duration of the experiment, that the experimental conditions have changed from
o3
4
CHOICE
BLOCKS OF TWO DAYS
FIGURE 2. The average numbers of bar-press responses under the fixed-ratio (FR) schedules prior to and after the introduction of free water.
the original training setting will produce the greatest amounts of freeloading. This effect should be independent of whether the change is to greater or lesser work terms. Those are precisely the data generated in the present setting. The animals remaining on the originally trained work terms, i.e., those not signaled of the change to a choice between earned and free water, continued to work in the presence of free water at a higher rate and for longer durations than the animals that were signaled of the change. These data suggest that an animal experiencing a change in work demands, regardless of whether to more difficult or less difficult terms via a change to the shorter or longer schedules, will demonstrate an increased level of freeloading relative to an animal maintained on the originally trained schedule. The results of the present experiments bear upon a most basic question in learning
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theory. That is, do animals in fact prefer the least effortful path to a goal? The contrafreeloading findings of a large number of studies (Neuringer, 1969, 1970; Singh, 1970) suggest quite the opposite. Animals will work for food or water, and sometimes will work quite hard, in the presence of the same reward freely available. The implication of the contrafreeloading phenomenon is that the learning theorist, and incentive theorist in particular, must invoke one or more additional assumptions to more realistically represent animal learning. For example, Jensen (1963) has suggested that bar pressing holds "intrinsic appeal" for a rat. Other investigators (Carder & Berkowitz, 1970) have proposed that "as long as the work demands are not too high" animals will prefer to earn their rewards freely. Hnally, Singh (1972) has implied that the Protestant work ethic is as basic to the rat as to man. Yet, are there more parsimonious explanations of the contrafreeloading phenomenon? The findings of the present experiments suggest that the contrafreeloading data can be accounted for with a basic learning principle. That is, the discriminability between the conditions of working and freeloading is a most important factor contributing to the continued responding in the presence of free rewards. The typical contrafreeloading paradigm (e.g., Carder & Berkowitz, 1970) is to teach an animal over several days to bar press in an operant box. Then free food is introduced. An animal is given brief exposure to the free food and then allowed to choose between working and freeloading. Yet one must consider that stimuli within the operant box environment have become discriminative stimuli in the presence of which the animal has previously been reinforced for bar pressing. Furthermore, the less the change in the stimulus situation with the introduction of free food, the slower the animal realizes the conditions have changed (Capaldi, 1967). Thus, the less the stimulus changes from the purely work condition to the choice between working and freeloading, the slower is the retardation of the bar-press response, i.e., the less the response decrement. Several other findings in the present
setting support the discriminability notion. First, animals made considerably more barpress responses in the presence of free water under the FR schedules than under the VI schedules. Informal observation of the animals suggested that during training the FR animals were much busier in the operant box than the VI rats. The FR animals seldom left the locus of the bar and, as a result, exhibited high levels of bar pressing during training. The VI animals, however, were much more likely to wander around the box during the experimental session. When free water was introduced, it was not surprising that the VI animals had a higher probability of discovering, and rediscovering periodically, the dish of free water than the generally "hardworking" FR animals. These observations confirm and extend the earlier observation (Taylor, 1972) that the few animals that genuinely preferred to bar press when free rewards were available were those animals that started pressing immediately upon being placed into the apparatus. Moreover, those rats remained at the bar for the largest portion of the session in the apparatus. Second, the animals, at least in the first experiment, that were not cued of the change in reinforcement conditions drank less water than the signaled animals. Again, there is the suggestion that the discriminability of the new reward source is a contributor to the contrafreeloading findings. Moreover, the data of the present experiments confirm the earlier findings that the animals gradually and predictably bar press less in the presence of free rewards over time (Taylor, 1972). That is, as the animals slowly learn that there is an easier, quicker source of the reward than bar pressing, they shift to the free rewards. After a few days the animals only infrequently bar press. Therefore, these data are quite in opposition to the earlier proposal (Carder & Berkowitz, 1970) that the difficulty of earning the reward determines the degree of working in the presence of free rewards. Neither is it necessary to speculate on the intrinsic appeal of bar pressing (Jensen, 1963) or of the work ethic (Singh, 1972). Instead, the present data suggest that one factor contributing to the continued responding in the presence
DISCRIMINABILITY AND CONTEAFREELOADING of free water is the discriminability between the original work condition and the subsequent freeloading condition. Many of the previous investigations in the contrafreeloading literature (Carder, 1972; Carder & Berkowitz, 1970; Neuringer, 1969, 1970; Stolz & Lott, 1964; Tarte & Snyder, 1972; 1973) are susceptible to interpretation from the parsimonious discrimination proposal. Finally, Mitchell and his associates (Mitchell, Scott, & Williams, 1973) have recently generated data to support their interpretation of contrafreeloading from an ethological viewpoint. They suggest that rats continue to bar press and receive food at a familiar source rather than eat free food at an unfamiliar source because the animals are neophobic. The present analyses are in essential agreement with their proposal. The "fear" of the newly introduced free-food source could simply be viewed as a lack of discriminability of the change in stimulus conditions, i.e., a lack of opportunity to learn the appropriate approach and consummatory responses to the free food. In summary, the seemingly troublesome contrafreeloading findings can be explained, at least to some extent, with a basic stimulus-response learning principle, discriminability of stimulus changes and its accompanying response decrement. REFERENCES Capaldi, E. J. A sequential hypothesis of instrumental conditioning. In K. W. Spenee & J. T. Spence (Eds.), The psychology of learning and motivation. New York: Academic Press, 1967. Carder, B. Rats preference for earned in comparison with free liquid reinforcers. Psychonomic Science, 1972, 26, 25-26.
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Carder, B., & Berkowitz, K. Rats preference for earned in comparison with free food. Science, 1970, 167, 1273-1274. Davidson, A. B. Factors affecting keypress responding by rats in the presence of free food. Psychonomic Science, 1971, 24, 135-137. Hull, C. L. Principles of behavior. New York: Appleton-Century-Crofts, 1943. Jensen, G. D. Preference of bar pressing over "freeloading" as a function of number of rewarded presses. Journal of Experimental Psychology, 1963, 65, 451-454. Logan, F. A. Incentive. New Haven: Yale University Press, 1960. Logan, F. A., & Wagner, A. R. Reward and punishment. Boston: Allyn & Bacon, 1965. Mitchell, D., Scott, D. W., & Williams, K. D. Container neophobia and the rats preference for earned food. Behavioral Biology, 1973, 9, 613-624. Neuringer, A. J. Animals respond for food in the presence of free food. Science, 1969,166, 399-401. Neuringer, A. J. Many responses per food reward with free food present. Science, 1970, 168, 503504. Singh, D. Preference for bar pressing to obtain reward over freeloading in rats and children. Journal of Comparative and Physiological Psychology, 1970, 73, 320-327. Singh, D. The pied piper vs the Protestant ethic. Psychology Today, 1972, 5, 53-56. Stolz, S. B., & Lott, D. F. Establishment in rats of a persistent response producing a net loss of reinforcement. Journal of Comparative and Physiological Psychology, 1964, 57, 147-149. Tarte, R. D., & Snyder, R. L. Bar-pressing in the presence of free food as a function of food deprivation. Psychonomic Science, 1972, 26, 169-170. Tarte, R. D., & Snyder, R. L. Some sources of variation in the bar pressing versus freeloading phenomenon in rats. Journal of Comparative and Physiological Psychology, 1973, 84, 128-133. Taylor, G. T. A limitation of the contrafreeloading phenomenon. Psychonomic Science, 1972, 29, 173-174. Tolman, E. C. Principles of performance. Psycliological Review, 1955, 62, 315-326. (Received September 19, 1973)
