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Bonobos appear to show little evidence of learning to make one response (R1) to an AB sequence and a different response (R2) to sequences BB, AA, and BA (Lind et al. PLoS ONE 18(9):e0290546, 2023), yet under different conditions, pigeons can learn this (Weisman et al. Exp Psychol Anim Behav Process 6(4):312, 1980). Aspects of the bonobo procedure may have contributed to this failure. Most important, no response was required in the presence of the stimuli to encourage attention to them. Furthermore, learning to make one response to the target sequence and another to the other sequences involves a bias that allows for better than chance responding. With the two-alternative forced-choice procedure used with the bonobos, the R1 response is correct for one sequence, whereas the R2 response is correct for three sequences. To correct for this, there are three times as many AB trials as each of the other sequences. However, this correction allows a bias to develop in which reinforcement often can be obtained by using only the last stimulus seen as the basis of choice (e.g., when the last stimulus is B respond R1 when the last stimulus is A respond R2). This solution yields reinforcement on five out of six, or 83%, of the trials. In the present experiment with pigeons, using this two-alternative forced choice procedure, most subjects tended to base their choice on the last-seen stimulus. This design allowed subjects to use a suboptimal but relatively effective choice strategy., (© 2024. The Author(s).)

Memory for what, where, and when an event took place has been interpreted as playing a critical role in episodic memory. Moreover, such memory is likely to be important to an animal's ability to efficiently forage for food. In Experiment 1 of the present study, pigeons were trained on a task in which on each trial, one lit stimulus color and location was presented and then another. A cue presented after the last stimulus location signaled that the pigeon was to choose either the first location presented, or the last location presented, to receive a reinforcer. After learning this task, in Experiment 2, the color cue was removed, requiring the pigeons to choose based on location and order alone. In Experiment 3, when a delay was inserted between presentation of the two locations, it had little effect on task accuracy. Results suggested that the pigeons had acquired the task using a single-code/default rule. When presented with the cue indicating that the last location was correct, pigeons selected the location just presented. When presented with the cue indicating that the first location was correct, pigeons chose the other location, by default. In support of this hypothesis, in Experiment 4, when a delay was inserted, prior to receiving the instructional cue, it had a disruptive effect on task accuracy proportional to the delay. Although the present results do not provide evidence for episodic memory, they do suggest that the pigeons have developed a single-code/default strategy that appears to be an efficient means of performing this task., (© 2023. The Psychonomic Society, Inc.)

In conditional discrimination, the conditional stimulus or sample indicates which of two choice or comparison stimuli is associated with a reinforcer. Two hypotheses have been proposed concerning the role of the sample stimulus. According to Hull (1952), the sample and the response to the correct comparison form a stimulus-response chain. According to Skinner (1938), however, the sample serves as an occasion setter, setting the occasion for the choice of the correct comparison stimulus. In a conditional discrimination, if the sample stimulus forms part of a stimulus-response chain, then presenting the sample in the absence of the comparison stimuli should weaken the association. If the sample serves as an occasion setter, however, presenting the sample alone should not weaken its occasion-setting ability. In two experiments we tested these predictions. In Experiment 1, following conditional discrimination training with vertical and horizontal line samples and red and green comparison stimuli, we found that the presentation of the samples without the comparison stimuli (followed sometimes by a reinforcer) had little effect on conditional discrimination accuracy. In Experiment 2, two different houselights served as samples. When we presented the samples without comparison stimuli and without the reinforcers we found similar results. The results support the hypothesis that in conditional discrimination, the samples serve as occasion setters. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

In a successive delay-discounting task, a small reward can be obtained immediately but a larger reward can be obtained if one waits. There is evidence that the larger reward can be obtained more easily if one is "distracted" from obtaining the small reward. It is proposed here that a distractor stimulus may function as a Pavlovian conditioned stimulus (sign tracking) because orienting to it may be directly associated with the larger reinforcer. In the present study with pigeons, we examined two successive procedures: (a) a peck to a red light resulted in one pellet of food, and waiting for the red light to turn off resulted in five pellets (Red-Only). (b) If the pigeon pecked a red light, it received one pellet of food, and if it waited for the red light to turn to green, a peck to the green light resulted in five pellets of food (Red-Green). For both groups, on some trials, a concurrent (distractor) stimulus appeared with the red light but responses to it had no programed consequence. Results indicated that the pigeons in both groups waited for the larger reward more often when the distractor was present than when it was absent and that pigeons in the Red-Only group waited longer than those in the Red-Green group. The results are consistent with the hypothesis that the concurrent stimulus served as a conditioned stimulus for the Red-Only group and as a higher order conditioned stimulus for the Red-Green group. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Humans can learn tasks explicitly, as they can often describe the rules they have used to learn the task. 1 , 2 , 3 Animals, however, are thought to learn tasks implicitly (i.e., purely associatively). 2 , 3 That is, they gradually learn the correlation or association between the stimulus (or response) and the outcome. Both humans and pigeons can learn matching, where a sample stimulus indicates which one of two stimuli matches the sample. The 1-back reinforcement task is a difficult version of matching in which a correct response on trial N is rewarded only following a response on trial N + 1 (independent of the response on trial N + 1), 4 and the correct response on trial N + 1 indicates whether a reward will occur on trial N + 2, and so forth. Humans do not appear to be able to learn the 1-back rule. 5 Pigeons, however, do show 1-back reinforcement learning, 6 , 7 and they appear to do so implicitly by gradually learning the correlation between their response on one trial and the outcome on the next trial (because all other relations are uncorrelated with the outcome). They learn the task slowly and to a level below what would be expected had they learned it explicitly. The present results, together with research with humans, 7 suggest that there are times when human explicit learning may interfere with the ability of humans to learn. Pigeons, however, are not "distracted" by attempts at explicit learning, and thus they are able to learn this and other similar tasks. 6 , 7 , 8 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

When pigeons learn matching-to-sample or nonmatching-to-sample there is good evidence that they can transfer that learning to novel stimuli. But early evidence suggests that in the rate of task acquisition, there is no benefit from a matching relation between the sample and the correct or incorrect comparison stimulus. In the present research we trained three groups of pigeons, each on two two-stimulus tasks simultaneously, matching-matching, nonmatching-nonmatching, or matching-nonmatching. If a common matching or nonmatching relationship benefits acquisition, the first two groups should acquire their tasks faster than the third group, for which the two tasks ought to be incompatible. The results indicated that all three groups acquired their tasks at about the same rate. A secondary goal of the experiment was to determine the basis of learning for the each of the three groups. During testing, for each task, there were test trials in which one of the stimuli from the other task replaced either the correct or the incorrect comparison stimulus. Surprisingly, neither comparison stimulus appeared to show complete control over comparison choice. Although replacing either comparison stimulus resulted in a decrement in task accuracy from about 90% to 70% correct, independent of which comparison stimulus was replaced, the pigeons chose correctly at well above chance accuracy. Suggestions to explain this unexpected outcome are discussed., (© 2022. The Psychonomic Society, Inc.)

Impulsive behavior can be measured by performance on a successive delay-discounting task, in which a response to a stimulus provides a small reinforcer sooner (SS), but in the absence of a response, a larger reinforcer later (LL). Previous research suggests that the presence of a concurrent "distractor" stimulus, to which responding has no programed consequence, can result in increased LL reinforcers. In the present experiments, we used differences in the probability of reinforcement between SS and LL (rather than magnitude of reinforcement) and tested the hypothesis that the concurrent stimulus may become a Pavlovian conditioned stimulus. For the Red-Only group, a response to the SS stimulus resulted in a reinforcer with a low probability (SS), whereas the absence of a response resulted in a reinforcer with a high probability (LL). For the Red-Green group, (analogous to the more typical simultaneous choice between an SS and LL stimulus) the absence of a response to the SS stimulus replaced the SS stimulus with the LL stimulus and a response to the LL stimulus resulted in the reinforcer. Thus, for the Red-Green group, the concurrent stimulus should have been less effective because responding to the concurrent stimulus was not immediately followed by the reinforcer. In Experiment 1, the concurrent stimulus was a yellow key-light; in Experiment 2, it was a houselight. In both experiments, the concurrent stimulus was effective in increasing the number of LL reinforcers and the effect was larger for the Red-Only group than for the Red-Green group., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Same/different learning by pigeons has been studied using several different procedures. One of these procedures is matching-to-sample or mismatching-from-sample in which responses to a sample stimulus result in the presentation of two comparison stimuli, one of which matches the sample, the other of which does not. In the matching task, choice of the matching stimulus is reinforced. In the mismatching task, choice of the stimulus that does not match the sample is reinforced. Most research that has compared acquisition of the two tasks has not reported a difference between them. Research with transfer of training, in which either the matching stimulus or the mismatching stimulus is replaced with a new stimulus, suggests that the matching stimulus is selected in the matching task, but the matching stimulus is rejected in the mismatching task. In the present experiment, pigeons were trained on either matching or mismatching with salient stimuli presented manually and the reinforcer was presented under a colored slide that covered it. In Phase 1 with a noncorrection procedure and a reinforcer for pecking the sample, pigeons did not acquire either task, however, in Phase 2 they learned both tasks readily without reinforcement for pecking the sample and with a correction procedure. Furthermore, the pigeons learned matching significantly faster than mismatching, suggesting that sameness may be a more natural stimulus relation than mismatching., (Copyright © 2022 Elsevier B.V. All rights reserved.)

When humans face probabilistic outcomes, their choices often depend on whether the choice is framed in terms of losses or gains. In the present research, we gave pigeons a choice between risky (variable) outcomes and safe (constant) outcomes that resulted in the same net reward. In Experiment 1, in which the outcomes represented a loss, the pigeons preferred the risky alternative. In Experiment 2, in which the outcomes represented a gain, the pigeons were indifferent between the two alternatives. In Experiment 3, in which the outcomes represented neither a gain nor a loss, the pigeons strongly preferred the risky alternative. The results were interpreted in terms of the relative value of gains and losses given to the alternatives by pigeons in the context of a risky and safe choice. In Experiment 4 we tested that hypothesis by giving pigeons a choice between a risky and safe alternative with the same net outcome, in the context of a gain associated with the safe alternative, but no gain or loss associated with the risky alternative. In support of the interpretation of the first three experiments, with the safe alternative associated with a gain, the pigeons now preferred the safe alternative. These results were discussed in terms of economic and foraging theories and were contrasted with the aversion to uncertainty (risk) more typically shown by humans., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

When pigeons learn a conditional discrimination in which a sample stimulus indicates which of two comparison stimuli is correct Skinner (1950) proposed that they learn a chain involving the sample, the correct comparison stimulus, and the reinforcer. This implies that they do not learn to reject the incorrect comparison stimulus and the sameness relation between the sample and the correct or the incorrect comparison stimulus plays little role in learning. There is, however, considerable evidence that learning to match or mismatch the sample can transfer to novel stimuli. But there is little evidence that the sameness relation facilitates acquisition. In the present research, pigeons were trained on two 0-s delay conditional discriminations: two matching tasks, two mismatching tasks, or one of each. No differences were found in acquisition, suggesting that consistent matching or mismatching does not facilitate acquisition of conditional discriminations. In testing, when either the correct or the incorrect comparison stimulus in each discrimination was replaced with one of the stimuli from the other task, results suggested that when learning both tasks, the pigeons in all three groups had learned both to select the correct stimulus and to reject the incorrect stimulus. It appears that the pigeons may have had learned the tasks based on sample/comparison-stimulus configurations with the sample serving as an occasion setter., Competing Interests: Declarations of interest None., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Pigeons typically prefer a 20% probability of signaled reinforcement over a 50% probability of unsignaled reinforcement. There is even evidence that they prefer 50% signaled reinforcement over 100% reinforcement. It has been suggested that this effect results from contrast between the expected probability of reinforcement (e.g., 50%) at the time of choice and the value of the positive signal for reinforcement (100%). Alternatively, it is primarily the value of the positive signal for reinforcement itself that determines suboptimal choice. To attempt to distinguish between these two hypotheses, in Experiment 1, we gave pigeons a choice between (a) a 50% reinforcement alternative that was followed by one of two signals for 100% reinforcement, each 25% of the time, or a signal for the absence of reinforcement 50% of the time (50% contrast) and (b) a 25% reinforcement alternative that was followed by a signal for 100% reinforcement 25% of the time, or a signal for the absence of reinforcement 75% of the time (75% contrast). In spite of the difference in contrast, the pigeons were indifferent between the two alternatives. In Experiment 2, when contrast was held constant at 50% and the value of the positive signals for reinforcement were different, we found support for choice based on the value of the positive signal for reinforcement. Thus, it appears that pigeons' choice depends primarily on the value of the outcome rather than its frequency or contrast. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

In human learning a distinction has been made between implicit and explicit learning. Implicit learning is thought involve automatic processes of the kind involved in Pavlovian conditioning, while explicit learning is thought to involve conscious hypothesis testing and rule formation, in which the ability to report the rule used to learn the task is taken as evidence. Because non-verbal animals cannot provide such evidence, several indirect methods have been proposed. One of these methods is faster learning by humans of certain explicitly learned tasks than implicitly learned tasks, but pigeons do not show a similar difference. Another method involves the 1-back-reinforcement conditional discrimination (if A choose X, if B choose Y) in which feedback following the conditional response is delayed until the next trial. It has been argued that implicit learning cannot occur over the delay between the conditional response and the reinforcer on the next trial, yet, it has been found that monkeys can learn this 1-back reinforcement task. We have argued that such learning can occur implicitly. We have found that pigeons, a species not thought to learn explicitly, can show significant learning of both 1-back reinforcement matching and 1-back reinforcement mismatching, two versions of the 1-back-reinforcement conditional discrimination. We propose that the evidence for explicit learning by non-verbal animals suffers from alternative simpler accounts because the rationale for explicit learning is based on assumptions that likely are not correct., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In humans, a distinction can be made between implicit or procedural learning (involving stimulus-response associations) and explicit or declarative learning (involving verbalizable rules) that is relatively easy to make in verbal humans. According to several investigators, it is also possible to make such a distinction in nonverbal animals. One way is by training them on a conditional discrimination task (e.g., matching-to-sample) in which reinforcement for correct choice on the current trial is delayed until after a choice is made on the next trial - a method known as the 1-back procedure. According to Smith, Jackson, and Church ( Journal of Comparative Psychology, 134(4), 423-434, 2020), the delay between the sample-correct-comparison response on one trial and reinforcement obtained on the next trial is too long for implicit (associative) learning. Thus, according to this theory, learning must be explicit. In the present experiments we trained pigeons using the 1-back procedure. In Experiment 1, pigeons were trained on red/green 1-back matching using a non-correction procedure. Some of the pigeons showed significant learning. When a correction procedure was introduced, all the pigeons showed evidence of learning. In Experiment 2, new pigeons learned red/green 1-back matching with the correction procedure. In Experiment 3, new pigeons learned symbolic 1-back matching with yellow and blue conditional stimuli and red/green choice stimuli. Thus, pigeons can learn using 1-back reinforcement. Although it would appear that the pigeons acquired this task explicitly, we believe that this procedure does not adequately distinguish between implicit and explicit learning., (© 2021. The Psychonomic Society, Inc.)

In the visual alternation task, pigeons learn to alternate between two stimuli (e.g., red and green) that vary randomly in location from trial to trial. The task is inherently difficult because animals tend to return to a stimulus to which they have just received reinforcement for responding. Williams (1971, Journal of the Experimental Analysis of Behavior, 15, 129-140) suggested that pigeons learn this task by learning to avoid the stimulus most recently chosen. The present experiment tested this hypothesis by involving three groups. The Standard Group replicated Williams' design. For the New Correct Group, following a correct (reinforced) response, on the next trial, the color of the new correct stimulus changed. For example, if it had been green, it changed to either blue or yellow, but the color of the new incorrect stimulus (the one that was just correct) remained the same (i.e., red). For the New Incorrect Group, following a correct response, on the next trial, the color of the new incorrect stimulus changed. For example, if it had been red, it changed to blue or yellow, but the color of the new correct stimulus remained (i.e., green). The Standard Group replicated Williams's finding that pigeons can learn the alternation task. Consistent with Williams's hypothesis, pigeons in the New Correct Group showed evidence of learning the alternation task, whereas pigeons in the New Incorrect Group showed little evidence of learning. Acquisition of the visual alternation task suggests that pigeons are cognitively flexible enough to overcome their natural tendency to repeat their most recently reinforced response to a stimulus., (© 2021. The Psychonomic Society, Inc.)

In a simultaneous discrimination, pigeons are presumed to learn to about the correct stimulus, but they may also learn to avoid the incorrect stimulus. Similarly, in a conditional discrimination, they are presumed to learn about the relation between the sample stimulus and the correct comparison stimulus but not about the incorrect comparison stimulus. In the present research, we encouraged pigeons to learn about the incorrect comparison stimulus by increasing, over trials, the number of correct comparison stimuli with one sample, to compare with increasing the number of incorrect comparison stimuli over trials with the other sample. In Experiment 1, using colors and shapes, we found no difference in acquisition between the 2 sample types. However, when we replaced either the correct or incorrect comparison from training with a novel stimulus, the pigeons showed that they had learned to avoid the incorrect comparison when there were multiple correct comparisons and to select the single correct comparison when there were multiple incorrect comparisons. In Experiment 2, using national flags as stimuli, when tested with a novel flag stimulus, once again, the pigeons learned about the single correct comparison but not about the multiple incorrect comparisons. However, with the other sample, they appeared to learn about both the multiple correct comparisons and about the single incorrect comparison. This research indicates that pigeons can show considerable flexibility in what they learn in a conditional discrimination. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

The reverse-contingency task is a task in which one is given a choice between two rewards, but one receives the larger amount only if one chooses the smaller amount. This task is very difficult for chimpanzees unless the choice is between symbolic representations of the amounts. We found that pigeons can learn this task easily, if the reward amounts are associated with distinctive colors and the choice is delayed by 5 s. The reverse-contingency task involves three components: a loss when choosing one alternative, a gain when choosing the other, and the contrast between what was expected and what occurred. In Experiment 2 we separated the loss from the gain and found that experiencing a loss is sufficient for pigeons to learn to avoid that alternative. Finally, we found evidence for perceived loss aversion. When pigeons were offered a small amount of food and they received that amount, they preferred it over an alternative that offered them a larger amount but gave them only the smaller amount (a perceived loss). The results indicate that loss aversion, based on reference dependence, is likely a general phenomenon, and not only found in humans and other primates. We suggest that it can be attributed to contrast, the difference between what is expected and what is obtained, and it is related to the endowment effect and the mere ownership effect found in humans.

In the midsession reversal task, pigeons are trained on a simultaneous two-alternative discrimination in which S1 is correct for the first half of the session and S2 is correct for the second half of the session. Optimally, pigeons should choose S1 until it stops being correct and choose S2 afterward. Instead, pigeons anticipate S2 too early and continue choosing S1 even after the reversal. Research suggests that they attempt to time the reversal rather than use the feedback from the preceding response(s). Recently, there is evidence that performance is almost optimized by generating an asymmetry between S1 and S2. For example, pigeons' accuracy improves if correct S1 responses are reinforced 100% of the time, but correct S2 responses are reinforced only 20% of the time. Similarly, accuracy improves if S1 requires one peck but S2 requires 10 pecks. Accuracy does not improve, however, if the value of S1 is less than the value of S2. In the current experiment, we manipulated the magnitude of reinforcement. For the experimental group, correct responses to S1 were reinforced with five pellets of food and correct responses to S2 were reinforced with one pellet. For the control group, all correct responses were reinforced with three pellets. Consistent with the earlier findings, results indicated that there was a significant reduction in anticipatory errors in the experimental group compared with the control, and there was no significant increase in perseverative errors.

Optimal foraging theory suggests that animals have evolved to maximize their net rate of energy intake; all things being equal, they should leave a current depleting patch when an alternative patch would provide either more or sooner food. In nature, however, typically all things are not equal. For example, uncertainty about the value of alternative patches, time to travel to those patches, and potential dangers incurred in changing patches may delay leaving the depleting patch, when it would otherwise be optimal to do so. We tested the hypothesis that leaving the current patch may be delayed, by providing pigeons (Columba livia) with a continuous choice between a progressive schedule, in which each access to food could be obtained with an increasing number of pecks, and a multiple schedule, in which a colored light signaled the number of pecks required for food. The pigeons could switch from the progressive schedule to the multiple schedule at any time. We asked if pigeons would tend to switch when the signaled multiple schedule required fewer pecks than the next reinforcer provided by the progressive schedule. We found that pigeons tended to switch to the multiple schedule sooner than would have been optimal-one might say they precrastinated. We propose that, on the progressive schedule, the signal to switch was not just the number of pecks required for the next reinforcer but also the more general cue that reinforcement was becoming more difficult to obtain-a form of serial pattern learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Reference dependence refers to the reduced value of a reward that is less than expected, or the added value of a reward that is greater than expected. There is evidence that when pigeons are offered an alternative that has 1 pellet versus an alternative that has 2 pellets, but one of the two pellets offered will be removed, the pigeons prefer the originally presented 1 pellet (loss aversion). In the present research, we tested for the opposite effect (gain attraction). In Experiments 1 and 2, pigeons could choose between 2 pellets, each one on a distinctive background. If they chose the optimal alternative, they received a second pellet. In Experiment 2, the second pellet obtained was the one not initially chosen (a task sometimes referred to as the ephemeral reward task). Pigeons learned to choose optimally in both experiments. In Experiment 3, we tested the pigeons for reference dependence. Pigeons were given an alternative that offered them one pellet or two pellets, if they chose the one-pellet alternative, they received an additional pellet, and if they chose the two-pellet alternative, they received the two pellets. In keeping with the reference dependence hypothesis, the pigeons preferred the 1-pellet alternative that gave them an extra pellet. These effects are related to similar findings with humans, including the endowment effect.

The traditional view of human procrastination is that engaging in an aversive task will be avoided until the anxiety associated with the consequences of missing the deadline exceeds the aversiveness of the task. Delay reduction theory suggests that there may be an additional mechanism, conditioned reinforcement associated with completion of the task close to the deadline. The results of several experiments support this hypothesis. First, we found support for the prediction of delay reduction theory that pigeons given equally long concurrent chains, prefer a chain involving a long fixed interval followed by a short fixed interval (followed by reinforcement) over a chain involving a short fixed interval followed by a long fixed interval (followed by reinforcement). In another experiment, to simulate a mildly aversive event, we added a dark gap between the two links in each of the chains and found the same result. Finally, consistent with delay reduction theory and with an analog of human procrastination, in a long box, we found that pigeons preferred to complete a response requirement on a panel closer to the goal (reinforcement) rather than closer to the start. The results of these experiments suggest that procrastination may be supported by conditioned reinforcement associated completion of a task close to the deadline., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In a midsession reversal task, the session begins with a simple simultaneous discrimination in which one stimulus (S1) is correct and the other stimulus (S2) is incorrect (S1+/S2-). At the midpoint of the session, the discrimination reverses and S2 becomes the correct choice (S2+/S1-). When choosing optimally, a pigeon should choose S1 until the first trial in which its choice is not reinforced and then it should shift to S2 (win-stay/lose-shift). With this task, pigeons have been shown to respond suboptimally by anticipating the reversal (making anticipatory errors) and continuing to choose S1 after the reversal (making perseverative errors). This suboptimal behavior may result from a pigeon's relative impulsivity due to the immediacy of reinforcement following choice. In other choice tasks, there is evidence that the introduction of a short delay between choice and reinforcement may decrease pigeons' impulsivity. In the present experiment, a delay was introduced between stimulus selection and reinforcement to assess whether it results in a decrease in anticipatory and perseverative errors. Pigeons that had a delay between choice and reinforcement were a bit slower in acquiring the midsession reversal task compared to those without a delay, but showed no decrease in either anticipatory or perseverative errors. It is likely that the pigeons' natural tendency to use time from the start of the session to the reversal as a cue to reverse prevented the delay from increasing accuracy on this task., (Copyright © 2020 Elsevier B.V. All rights reserved.)

When humans procrastinate, they delay completing a required relatively aversive task. In the present experiments with pigeons, we considered the possibility that completing the task close to the deadline results in the formation of a stronger conditioned reinforcer. In Experiment 1, pigeons were given a choice between two chains: (a) a signaled long period, followed by a dark gap, followed by a signaled short conditioned reinforcer, and food and (b) a signaled short period, followed by a dark gap, followed by a signaled long conditioned reinforcer, and food. We found a reliable preference for the delayed gap. In Experiment 2, we let pigeons choose between two chains: (a) walking to a near panel to peck a key, followed by a long walk to peck a key for reinforcement and (b) walking to a far panel to peck a key followed by a short walk to peck a key for reinforcement. When a single peck was required to either key, the pigeons were indifferent. When ten pecks were required to the near key but only one peck to the far key, the pigeons preferred the far key. When ten pecks were required to either key, the pigeons preferred the far key. The results of both experiments suggest that pigeons prefer to defer a relatively aversive event but, in keeping with Fantino's Delay Reduction Theory, this effect may result from the development of a strong conditioner reinforcer that occurs when the event (the gap or required pecking) comes close to reinforcement.

In the midsession reversal task, choice of one stimulus (S1) is correct for the first half of each session and choice of the other stimulus (S2) is correct for the last half of each session. Although humans and rats develop very close to what has been called a win-stay/lose-shift response strategy, pigeons do not. Pigeons start choosing S2 before the reversal, making anticipatory errors, and they keep choosing S1 after the reversal, making perseverative errors. Research suggests that the pigeons are timing the reversal from the start of the session. However, making the reversal unpredictable does not discourage the pigeons from timing. Curiously, pigeons' accuracy improves if one decreases the value of the S2 stimulus relative to the S1 stimulus. Another form of asymmetry between S1 and S2 can be found by varying, over trials, the number of S1 or S2 stimuli. Counterintuitively, if the number of S2 stimuli varies, it results in a large increase in anticipatory errors but little increase in perseverative errors. However, if the number of S1 stimuli varies over trials, it results in a large increase in perseverative errors but no increase in anticipatory errors. These last two effects suggest that in the original midsession reversal task, the pigeons are learning to reject S2 during the first half of each session and learning to reject S1 during the last half of each session. These results suggest that reject learning may also play an important role in the learning of simple simultaneous discriminations.

Delaying reinforcement typically has been thought to retard the rate of acquisition of an association, but there is evidence that it may facilitate acquisition of some difficult simultaneous discriminations. After describing several cases in which delaying reinforcement can facilitate acquisition, we suggest that under conditions in which the magnitude of reinforcement is difficult to discriminate, the introduction of a delay between choice and reinforcement can facilitate the discrimination. In the present experiment, we tested the hypothesis that the discrimination between one pellet of food for choice of one alternative and two pellets of food for choice of another may be a difficult discrimination when choice consists of a single peck. If a 10-s delay occurs between choice and reinforcement, however, the discrimination is significantly easier. It is suggested that when discrimination between the outcomes of a choice is difficult and impulsive choice leads to immediate reinforcement, acquisition may be retarded. Under these conditions, the introduction of a brief delay may facilitate acquisition.

The midsession reversal task involves a simple simultaneous discrimination in which, each session, choice of 1 stimulus (S1) is correct for the first 40 trials of each session, and choice of the other stimulus (S2) is correct for the remaining 40 trials. After considerable training with this task, pigeons typically continue to choose S2 too early (making anticipatory errors) and continue choosing S1 for following the reversal (making perseverative errors). Errors can be reduced, however, by decreasing the probability of reinforcement for correct S2 choices or by increasing the response requirement for S2 choices. Increasing the number of S2 stimuli (over trials, 1 S2 stimulus on each trial), however, does not reduce errors. Instead, it results in an increase in anticipatory errors but no change in perseverative errors. In the present experiment, we increased the number of S1 stimuli (over trials, 1 S1 stimulus on each trial) and found an increase in the number of perseverative errors but no change in anticipatory errors. The results suggest that the pigeons acquire this task by learning which stimuli to avoid, rather than which stimuli to choose, although it is also possible that these effects result from attention drawn to the variable stimuli when they are incorrect. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

The midsession reversal task involves a simultaneous discrimination in which choice of one stimulus (S1) is correct for the first 40 trials and choice of the other stimulus (S2) is correct for the last 40 trials of each 80-trial session. When pigeons are trained on the midsession reversal task, they appear to use the passage of time from the start of the session as a cue to reverse. As the reversal approaches, they begin to make anticipatory errors, choosing S2 early, and following the reversal they make perseverative errors, continuing to choose S1. Recent research suggests that anticipatory errors can be reduced (while not increasing perseverative errors) by reducing the probability of reinforcement for correct S2 choices from 100% to 20%. A similar effect can be found by increasing the response requirement for choice of S2 from one peck to ten pecks. In the present experiments, we asked if a similar effect could be attained by increasing the number of stimuli that, over trials, could serve as S2. Instead, in both experiments, we found that increasing the number of S2 stimuli actually increased the number of anticipatory errors. Several interpretations of this result are provided, including the possibility that attention to the variable S2 stimuli may have interfered with attention to the S1 stimulus.

The midsession reversal task involves a simultaneous discrimination between Stimulus 1 (S1) and Stimulus 2 (S2) in which, for the first half of each session, choice of S1 is reinforced and S2 is not, and for the last half of each session, choice of S2 is reinforced and S1 is not. With this task, even after considerable training, pigeons tend to make anticipatory errors as they approach the reversal and they continue to make perseverative errors following the reversal. In the present research, we tested the hypothesis that reversal accuracy would improve by devaluing choice of S2 relative to S1. In Experiment 1, correct choice of S1 was reinforced 100% of the time, whereas correct choice of S2 was reinforced only 20% of the time. This manipulation reduced anticipatory errors but did not increase perseverative errors. In Experiment 2, choice of S1 required a single peck, whereas choice of S2 was devalued by requiring 10 pecks. A similar result was found. In Experiment 3 we devalued S1 by requiring 10 pecks and found decreased accuracy in the form of increased anticipatory errors. Paradoxically, in Experiments 1 and 2, by encouraging the pigeons to avoid using the feedback from choice of S2, and rely solely on feedback from choice of S1, discrimination reversal errors were reduced. The results have implications for attentional theories of learning and theories of behavior change. They also have implications for the conditions responsible for pigeons' tendency to time the occurrence of the change in reinforcement contingencies. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Animals are expected to minimize time and effort to reinforcement. Thus, not pecking should be preferred over pecking. However, even if time is held constant, pigeons often peck when it is allowed but not required (e.g., fixed time schedules), but with such schedules pecking may be adventitiously reinforced. In the present experiment, to better compare a schedule of reinforcement that requires pecking with one that requires the absence of pecking, we compared a modified fixed-interval (FI) schedule in which reinforcement follows the first peck after the interval has elapsed and a differential-reinforcement-of-other behavior (DRO) schedule, which requires pigeons to abstain from pecking for a similar interval. The delay to reinforcement was matched on a trial-by-trial basis by yoking the duration of the FI to match the DRO schedule that preceded it. Of 12 pigeons, six preferred the DRO schedule over the FI schedule and six did not show a schedule preference. Those that were indifferent between the schedules apparently had a stronger spatial preference than their schedule preference. Individual differences in the preference of the pigeons may have been related to their behavior during the DRO schedule.

Object permanence, often viewed as a measure of human cognitive development, has also been used to assess animals' cognitive abilities. Tests of object permanence have distinguished between visible displacement, in which an object may be placed into one of two (or more) containers to be retrieved, and invisible displacement, in which after the object is placed into the container, the container is moved before retrieval is attempted. We tested pigeons' accuracy on both visible and invisible displacement using a rotational beam with a container at either end. In Experiment 1, the pigeons showed some evidence of object permanence on an initial visible displacement test, but they did not maintain accurate choice. With training, their accuracy improved but only to about 70% correct. When tested on a 90° invisible displacement (rotation), accuracy transferred but once again dropped with further training. In Experiment 2, a 5-s delay was inserted between container baiting and choice. Once again, the pigeons showed some evidence of object permanence on an initial visible displacement test, although on the first test session, choice accuracy was not much better than in Experiment 1. With training, choice accuracy improved greatly. Furthermore, pigeons showed good transfer when they were tested on the 90° invisible displacement. Finally, and importantly, they also transferred well to a 180° invisible displacement, a displacement on which dogs failed. The results of these experiments suggest that under the right conditions, pigeons can show a moderate degree of object permanence. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Timberlake (1993) proposed that much learning research can be better understood in the context of behavior systems theory. Learning theories generally have not considered how procedures may interact with evolutionarily prepared foraging contexts, thereby leading to anomalous conclusions. An example of such a conclusion is the apparent species difference when given a choice between a lower percentage of signaled reinforcement (20%) and higher percentage of unsignaled reinforcement (50%). Pigeons generally show a preference for the suboptimal alternative. Rats, however, often choose optimally. Orduña et al. have suggested that rats choose optimally because they show conditioned inhibition to signals for nonreinforcement, whereas pigeons do not. We suggest, however, that such fundamental species differences are unlikely. Rather, differences in the search mode elicited by the stimuli, together with some generalization between the signals for reinforcement and nonreinforcement are more likely to account for the species differences in suboptimal choice. When we used a retractable lever as the signal for reinforcement and a light stimulus as the signal for nonreinforcement, the rats showed suboptimal choice, not unlike that of pigeons. In this case, how the conditioned stimuli conform to the animals' behavior systems natural predispositions appears to affect how the animals react to those stimuli. Thus, when the search modes are matched between species and there is no generalization between the two signals, similar behavior can be found. Timberlake's contribution of behavior systems provides an evolutionary context in which species differences in sensory, response, and motivational differences can be separated from learning differences., (Copyright © 2018 Elsevier B.V. All rights reserved.)

When pigeons are given a choice between 50% signaled reinforcement and 100% reinforcement they typically do not choose optimally, sometimes even preferring 50% reinforcement. Smith and Zentall (J Exp Psychol Anim Behav Process 42:212-220, 2016) proposed that choice depends primarily on the predictive value of the signal for reinforcement associated with each alternative (both 100% reinforcement) and not the frequency of the signal for reinforcement (50% vs. 100%). With extended training, however, Case and Zentall (Behav Process, 2018) found that pigeons actually show a reliable preference for the 50% reinforcement alternative. They suggested that contrast between the expected outcome at the time of choice (50% reinforcement) and the value of the signal for reinforcement (100% reinforcement) is the mechanism responsible for the preference for the suboptimal alternative (for the optimal alternative there should be no contrast). In the present research, we tested the contrast hypothesis by increasing the probability of reinforcement for choice of the suboptimal alternative to 75%, thereby reducing the contrast between expected and obtained reinforcement and found a reduced preference for the suboptimal alternative. That is, increasing the probability of reinforcement for choice of the suboptimal alternative decreased suboptimal choice. Thus, preference for the suboptimal alternative appears to result from two mechanisms: (1) the value of the signal for reinforcement that follows choice of the alternative and (2) positive contrast between the expected and obtained probability of reinforcement. We compared this interpretation with other hypotheses.

Prior research has found that pigeons are indifferent between an option that always provides a signal for reinforcement and an alternative that provides a signal for reinforcement only 50% of the time (and a signal for the absence of reinforcement 50% of the time). This suboptimal choice suggests that the frequency of the signal for reinforcement plays virtually no role and choice depends only on the predictive value of the signal for reinforcement associated with each alternative. In the present research we tested the hypothesis that if there are two or three signals for reinforcement associated with the suboptimal alternative but each occurs only 25% or 17% of the time, respectively, pigeons would show a greater preference for the suboptimal alternative. Although we found that increasing the number of signals for reinforcement associated with the suboptimal alternative did not increase the preference for the suboptimal alternative (relative to a single signal for reinforcement) extended training on this task resulted in a significant preference for the suboptimal alternative by both groups. This result suggests that contrast between the expected outcome at the time of choice (50% reinforcement) and the value of the signal for reinforcement (100% reinforcement) is also responsible for choice of the suboptimal alternative., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Procrastination is the tendency to put off initiation or completion of a task. Although people are typically known to procrastinate, recent research suggests that they sometimes "pre-crastinate" by initiating a task sooner than they need to (Rosenbaum et al. in Psychological Science, 25(7), 1487-1496, 2014). A similar finding of precrastination was reported by Wasserman and Brzykcy (Psychonomic Bulletin & Review, 22, 1130-1134, 2015) with pigeons using a somewhat different procedure. In the present experiment, we used a procedure with pigeons that was more similar to the procedure used by Rosenbaum et al. Pigeons were given a choice between two sequences of events (concurrent chains). Choice of the procrastination chain resulted in color A, which 15-s later would change to color B and 5-s later resulted in reinforcement. Choice of the precrastination chain resulted in color C, which 5-s later would change to color D and 15-s later resulted in reinforcement. Thus, both chains led to reinforcement after 20 s. Results indicated that the pigeons procrastinated. That is, they preferred the 15-5 chain over the 5-15 chain. The results are consistent with Fantino's (Journal of the Experimental Analysis of Behavior, 12, 723-730, 1969) delay reduction theory, which posits that stimuli that signal a reduction in the delay to reinforcement, such as the 5-s stimulus that occurred immediately prior to reinforcement, serve as strong conditioned reinforcers and should be preferred. In support of this theory, the pigeons pecked most at the 5-s stimulus that led immediately to reinforcement, indicating that it had become a strong conditioned reinforcer. The results suggest that delay reduction theory, a theory that emphasizes the attraction to stimuli that predict reinforcement with a short delay, also may contribute to human procrastination behavior because when task completion comes just before the deadline, it may become a stronger conditioned reinforcer than if task completion comes earlier.

It has been assumed that when pigeons learn how to match to sample, they learn simple stimulus-response chains but not the concept of sameness. However, transfer to novel stimuli has been influenced by pigeons' tendency to be neophobic. We trained pigeons on matching ( n = 7) and mismatching ( n = 8) with colors as samples and, with each sample, one color as the nonmatching comparison. We then replaced either the matching or the nonmatching stimulus with a familiar stimulus never presented with that sample. Results suggest that for both matching and mismatching, pigeons locate the stimulus that matches the sample: If the task involves matching, they chose it; if it involves mismatching, they avoid it. Thus, the concept of sameness is the basis for correct choice with both tasks. This finding suggests that sameness is a basic concept that does not have to be learned and may have evolved in many species, including humans.

Most models of choice assume a "tug of war" (ToW) between options present at the time of the choice, arguing that preferences are built on this process, and implying that adding options increases delay to act. In contrast, the sequential choice model (SCM) proposes that choices are driven by parallel expression of the mechanisms that control action in sequential encounters, without comparative deliberation at choice time. Only the SCM predicts choice preferences based on latencies to respond in single-option encounters. SCM further predicts that latencies to choose should either be the same or shorter than those in sequential encounters. We contrasted these models using a midsession reversal task with pigeons. Responses to one alternative (S1) were rewarded in the first half of each session and those to the other (S2) in the second half. Single-option (sequential) and two-option (choice) trials were intermingled. In choice trials subjects strongly preferred S1 early in the session, showed intermediate preferences toward the midsession, and preferred S2 late. These preferences were all predicted by changes in latency toward the presently negative alternative (S2 early and S1 late) in single-option trials. Latency toward presently positive stimuli were minimal throughout, in both single and two option trials, with no evidence of an evaluation time cost of choice. The ability to predict choice preference from latencies in sequential encounters and the absence of a choice delay support the SCM against ToW models, consistently with results from other protocols and species. (PsycINFO Database Record, ((c) 2018 APA, all rights reserved).)

Individuals often face choices that have uncertain outcomes and have important consequences. As a model of this environment, laboratory experiments often offer a choice between an uncertain, large reward that varies in its probability of delivery against a certain but smaller reward as a measure of an individual's risk aversion. An important factor generally lacking from these procedures are gambling related cues that may moderate risk preferences. The present experiment offered pigeons choices between unreliable and certain rewards but, for the Signaled group on winning choices, presented a 'jackpot' signal prior to reward delivery. The Unsignaled group received an ambiguous stimulus not informative of choice outcomes. For the Signaled group, presenting win signals effectively blocked value discounting for the large, uncertain outcome as the probability of a loss increased, whereas the Unsignaled group showed regular preference changes similar to previous research lacking gambling related cues. These maladaptive choices were further shown to be unaffected by more salient loss signals and resistant to response cost increases. The results suggest an important role of an individual's sensitivity to outcome-correlated cues in influencing risky choices that may moderate gambling behaviors in humans, particularly in casino and other gambling-specific environments.

Prior commitment has been found to facilitate choice of a larger later reward (e.g., healthy living) and avoid the impulsive choice of the smaller immediate reward (e.g., smoking, drug taking). In this research with pigeons, we investigated the ephemeral choice task in which pigeons are given a choice between two alternatives, A and B, with similar reinforcement provided for each; however, if they choose A, they can also choose B, whereas if they choose B, A is removed. Thus, choosing A gives them two rewards, whereas choosing B gives them only one. Paradoxically, pigeons actually show a preference for B, the suboptimal alternative. We tested the hypothesis that pigeons made suboptimal choices because they were impulsive. To reduce impulsivity, we required the pigeons to make their initial choice 20 s before receiving the first reward. We found that requiring the pigeons to make a prior commitment encouraged them to choose optimally. The control group, for which the reward was provided immediately following initial choice, continued to choose suboptimally. The results confirm that requiring animals to make a prior commitment can facilitate the development of optimal choice. Furthermore, they may help explain why, without prior commitment, impulsive species, such as primates and pigeons have difficulty with this task, whereas presumably less impulsive species, such as wrasse fish and under some conditions parrots, are able to choose optimally even without prior commitment.

Slot machines are among the most popular forms of commercial gambling, and the high frequency of losses that come close to winning - near hits - in this game appears to contribute to its popularity. In the present experiment we tested if pigeons, similarly to humans, prefer an alternative that provides near-hit outcomes in a slot-machine-like task. The pigeons received series of three stimuli, one every two seconds: if the three stimuli matched, food was delivered (a win); if they did not match, food was not delivered (a loss). We gave pigeons a choice between two options that provided food with the same probability but they differed in the sequence of stimuli on loss trials. For the near-hit alternative the non-matching stimulus was the third one (defined as a near hit). For the clear-loss alternative the non-matching stimulus was the second one. We found that the pigeons preferred the clear-loss alternative, that is, they preferred to be given information about the outcome sooner. This result is consistent with prior research on suboptimal choice with pigeons that emphasizes the role of information in choice but is inconsistent with the results of research with humans., (Copyright © 2017 Elsevier B.V. All rights reserved.)

There is evidence that impulsive decision-making is associated with errors in timing. However, there has been little attempt to identify the putative mechanism responsible for impulsive animals' timing errors. One means of manipulating impulsivity in non-human animals is providing different levels of access to conspecifics. These preclinical models have revealed that social isolation increases impulsive responding across a wide range of tasks. The goal of the present study was to determine whether social isolation modulates time perception in pigeons by inducing more variability or a bias to underestimate the passage of time in temporal judgments. A temporal bisection task was used to characterize time perception. One group of pigeons performed the bisection following social enrichment, and the remaining half of the pigeons were tested following social isolation. Results revealed pigeons in the social isolation condition categorized a temporal stimulus sample as "long" at shorter durations than pigeons in the social enrichment condition. These data highlight the mechanism(s) thought to underlie timing-based interventions aimed at reducing impulsivity in humans. Future work should consider whether impulsivity is produced by misperceptions of time or a reduced threshold for a response.

Pigeons have shown suboptimal gambling-like behavior when preferring a stimulus that infrequently signals reliable reinforcement over alternatives that provide greater reinforcement overall. As a mechanism for this behavior, recent research proposed that the stimulus value of alternatives with more reliable signals for reinforcement will be preferred relatively independently of their frequencies. The present study tested this hypothesis using a simplified design of a Discriminative alternative that, 50% of the time, led to either a signal for 100% reinforcement or a blackout period indicative of 0% reinforcement against a Nondiscriminative alternative that always led to a signal that predicted 50% reinforcement. Pigeons showed a strong preference for the Discriminative alternative that remained despite reducing the frequency of the signal for reinforcement in subsequent phases to 25% and then 12.5%. In Experiment 2, using the original design of Experiment 1, the stimulus following choice of the Nondiscriminative alternative was increased to 75% and then to 100%. Results showed that preference for the Discriminative alternative decreased only when the signals for reinforcement for the two alternatives predicted the same probability of reinforcement. The ability of several models to predict this behavior are discussed, but the terminal link stimulus value offers the most parsimonious account of this suboptimal behavior.

Recent research has examined a task in which choice of 1 alternative A provides reinforcement and in addition, allows access to alternative B that also provides reinforcement. However, although initial choice of B also provides reinforcement, it does not also allow access to A. Thus, optimal performance would be to always choose A. Curiously, Salwiczek et al. (2012) reported that adult wrasse (cleaner) fish mastered this task within 50 trials, whereas monkeys and apes had great difficulty with it. The authors attributed the species differences to ecological differences in the species foraging experiences. However, Pepperberg and Hartsfield (2014) found that parrots too learned this task. In Experiment 1, using the manual presentation of stimuli, we found that pigeons actually showed a reliable preference for B, the suboptimal alternative. In Experiment 2, we replicated the suboptimal preference using an automated version of the task. We hypothesized that the pigeons may have been basing their preference on the frequency of reinforcement associated with each alternative (initially, all trials ended with choice of B, whereas only half of the trials involved choice of A). In Experiment 3, we tested the hypothesis that the pigeons' preference was influenced by the frequency of reinforcements associated with A and B. Thus, when the pigeon chose A, we replaced B with C, so reinforcement occurred to B only when they chose it first. With this procedure we found that B was no longer preferred over A. Thus, the data supported our hypothesis. (PsycINFO Database Record, ((c) 2016 APA, all rights reserved).)

The midsession reversal task involves a simple simultaneous discrimination that predictably reverses midway through a session. Under various conditions, pigeons generally both anticipate the reversal and perseverate once it has occurred, whereas rats tend to make very few of either kind of error. In the present research, we investigated the hypothesis that the difference in performance between rats and pigeons is related to the nature of the responses made. We hypothesized that rats could have been better at bridging the intertrial interval by keeping the relevant paw close to the lever while eating, whereas the pigeons had to remove their beak from the response key and insert it into the feeder, thus making it difficult to mediate the response last made. In the present experiment, in successive phases, rats were trained to leverpress or nose-poke on a 40-trial midsession reversal, an 80-trial midsession reversal, and a variable-location reversal. The results showed that the leverpress group acquired the task faster than the nose-poke group, but that both groups reached comparable levels of performance. Thus, the difference in the natures of the responses cannot fully account for the differences in accuracy between rats and pigeons. Additionally, differences in the types of errors made by the two groups suggest that the nature of the response plays different roles in the performance of this task.

Delayed matching-to-sample is a versatile task that has been used to assess the nature of animal memory. Although once thought to be a relatively passive process, matching research has demonstrated considerable flexibility in how animals actively represent events in memory. But delayed matching can also demonstrate how animals fail to maintain representations in memory when they are cued that they will not be tested (directed forgetting) and how the outcome expected can serve as a choice cue. When pigeons have shown divergent retention functions following training without a delay, it has been taken as evidence of the use of a single-code/default coding strategy but in many cases an alternative account may be involved. Delayed matching has also been used to investigate equivalence learning (how animals represent stimuli when they learn that the same comparison response is correct following the presentation of two different samples) and to test for metamemory (the ability of pigeons to indicate that they understand what they know) by allowing animals to decline to be tested when they are uncertain that they remember a stimulus. How animals assess the passage of time has also been studied using the matching task. And there is evidence that when memory for the sample is impaired by a delay, rather than use the probability of being correct for choice of each of the comparison stimuli, pigeons tend to choose based on the overall sample frequency (base-rate neglect). Finally, matching has been used to identify natural color categories as well as dimensional categories in pigeons. Overall, matching to sample has provided an excellent methodology for assessing an assortment of cognitive processes in animals., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In the Monty Hall dilemma, humans are initially given a choice among three alternatives, one of which has a hidden prize. After they have chosen, but before revealing whether they have won the prize, subjects are shown that one of the remaining alternatives does not have the prize, and they are asked whether they want to stay with their original choice or switch to the remaining alternative. Switching results in obtaining the prize two thirds of the time, but even after considerable training, humans fail to consistently adopt the optimal strategy of switching. Pigeons, however, show closer-to-optimal switching performance with this task. One of the reasons that humans choose suboptimally is their mistaken assumption that with two alternatives, the probabilities of winning the prize are the same for staying and switching, and staying may be preferred because of a sense of endowment (ownership of the initial response). When we tried to produce an endowment effect in pigeons by requiring 20 pecks (rather than one peck) for the initial choice, it actually resulted in faster acquisition of the switching response. In the present research with pigeons, we examined the finding from human research that subjects are more likely to switch if they are not responsible for making the initial choice (another approach to the endowment effect). Inconsistent with the findings with humans, we found that when the initial choice was made for the pigeons, they actually showed less of a tendency to switch than did pigeons that made the initial choice themselves.

Pigeons show suboptimal choice on a gambling-like task similar to that shown by humans. Humans also show a preference for gambles in which there are near hits (losses that come close to winning). In the present research, we asked if pigeons would show a preference for alternatives with near-hit-like trials. In Experiment 1, we included an alternative that presented a near hit, in which a stimulus associated with reinforcement (a presumed conditioned reinforcer) changed to a stimulus associated with the absence of reinforcement (a presumed conditioned inhibitor). The pigeons tended to avoid this alternative. In Experiment 2, we varied the duration of the presumed conditioned reinforcer (2 vs. 8 s) that changed to a presumed conditioned inhibitor (8 vs. 2 s) and found that the longer the conditioned reinforcer was presented, the more the pigeons avoided it. In Experiment 3, the near-hit alternative involved an ambiguous stimulus for 8 s that changed to a presumed conditioned reinforcer (or a presumed conditioned inhibitor) for 2 s, but the pigeons still avoided it. In Experiment 4, we controlled for the duration of the conditioned reinforcer by presenting it first for 2 s followed by the ambiguous stimulus for 8 s. Once again, the pigeons avoided the alternative with the near-hit trials. In all 4 experiments, the pigeons tended to avoid alternatives that provided near-hit-like trials. We concluded that humans may be attracted to near-hit trials because near-hit trials give them the illusion of control, whereas this does not appear to be a factor for pigeons., ((c) 2015 APA, all rights reserved).)

When humans are asked to judge the value of a set of objects of excellent quality, they often give this set higher value than those same objects with the addition of some of lesser quality. This is an example of the affect heuristic, often referred to as the less-is-more effect. Monkeys and dogs, too, have shown this suboptimal effect. But in the present experiments, normally hungry pigeons chose optimally: a preferred food plus a less-preferred food over a more-preferred food alone. In Experiment 2, however, pigeons on a less-restricted diet showed the suboptimal less-is-more effect. Choice on control trials indicated that the effect did not result from the novelty of two food items versus one. The effect in the less-food-restricted pigeons appears to result from the devaluation of the combination of the food items by the presence of the less-preferred food item. The reversal of the effect under greater food restriction may occur because, as motivation increases, the value of the less-preferred food increases faster than the value of the more-preferred food, thus decreasing the difference in value between the two foods.

In studies of transitive inference (TI), nonhuman animals are typically trained with the following 5-term task: A+B-, B+C-, C+D-, D+E- where the letters stand for arbitrary stimuli and [+] indicates that choice is reinforced and [-] indicates that choice is not reinforced. A TI effect is found when, given the untrained test pair BD, subjects choose B. TI effects have been found in many nonhuman species. Although reinforcement history has been posited as an account of the TI effect, it has failed to account for a variety of conditions under which TI effects have been found. A more cognitive account of TI is that organisms are able to form a representation of the series (A>B>C>D>E). In support of this hypothesis, Roberts and Phelps (Psychol Sci 5:368-374, 1994) found that presentation of the pairs of stimuli in a linear arrangement facilitated TI performance by rats, whereas presentation of the pairs of stimuli in a circular arrangement did not. Using methods adapted from Roberts and Phelps, we trained pigeons on either a linear or a circular arrangement of stimuli with the 5-term task. Results indicated that on the BD test pair, pigeons trained with a circular arrangement did not differ from those trained with a linear arrangement. Furthermore, we found that memory for training pairs was variable and was highly correlated with degree of TI. The results suggest that regardless of how pigeons are able to represent the stimuli, choice was not affected by the spatial arrangement of the stimuli during training.

Human gambling often involves the choice of a low probability but high valued outcome over a high probability (certain) low valued outcome (not gambling) that is economically more optimal. We have developed an analog of gambling in which pigeons prefer a suboptimal alternative that infrequently provides a signal for a high probability (or high magnitude) of reinforcement over an optimal alternative that always provides a signal for a lower probability (or lower magnitude) of reinforcement. We have identified two mechanisms that may be responsible for this suboptimal behavior. First, the effect of nonreinforcement results in considerably less inhibition of choice than ideally it should. Second, the frequency of the occurrence of the signal for a high probability or high magnitude of reinforcement is less important than ideally it should. Also analogous to human gambling is the finding that pigeons that are normally food restricted choose suboptimally, whereas those that are minimally food restricted choose optimally. In addition, pigeons that are singly housed choose suboptimally, whereas those that are exposed to a more enriched environment choose less suboptimally. We believe that these findings have implications for the understanding and treatment of problem gambling behavior., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Pigeons prefer a low-probability, high-payoff but suboptimal alternative over a reliable low-payoff optimal alternative (i.e., one that results in more food). This finding is analogous to suboptimal human monetary gambling because in both cases there appears to be an overemphasis of the occurrence of the winning event (a jackpot) and an underemphasis of losing events. In the present research we found that pigeons chose suboptimally to the degree that they were impulsive as indexed by the steeper slope of the hyperbolic delay-discounting function (i.e., the shorter the delay they would accept in a smaller-sooner/larger-later procedure). These correlational findings have implications for the mechanisms underlying suboptimal choice by humans (e.g., problem gamblers) and they suggest that high baseline levels of impulsivity can enhance acquisition of a gambling habit.

Pigeons prefer an alternative that provides them with a stimulus 20% of the time that predicts 10 pellets of food and a different stimulus 80% of the time that predicts 0 pellets, over an alternative that provides them with a stimulus that always predicts 3 pellets of food, even though the preferred alternative provides them with considerably less food. It appears that the stimulus that predicts 10 pellets acts as a strong conditioned reinforcer, despite the fact that the stimulus that predicts 0 pellets occurs 4 times as often. In the present research, we tested the hypothesis that early in training conditioned inhibition develops to the 0-pellet stimulus, but later in training it dissipates. We trained pigeons with a hue as the 10-pellet stimulus and a vertical line as the 0-pellet stimulus. To assess the inhibitory value of the vertical line, we compared responding to the 10-pellet hue with responding to the compound of the 10-pellet hue and the vertical line early in training and once again late in training, using both a within-subject design (Experiment 1) and a between-groups design (Experiment 2). We found that there was a significant reduction in inhibition between the early test (when pigeons chose optimally) and late test (when choice was suboptimal). Thus, the increase in suboptimal choice may result from the decline in inhibition to the 0-pellet stimulus. Implications for human gambling behavior are considered.