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Highlights • Pigeons show suboptimal choice between 50% signaled and 100% reinforcement. • The value of each of the positive stimuli accounts for most of the effect. • Contrast between expected and obtained reinforcement contributes to the effect. • The number of positive stimuli associated with the suboptimal alternative does not. Abstract 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. [ABSTRACT FROM AUTHOR]

Animals choose suboptimally when provided with cues that signal whether reinforcement is coming or not. For example, pigeons do not prefer an alternative that always provides them with a signal for reinforcement over an alternative that provides them with a signal for reinforcement only half of the time and a signal for the absence of reinforcement the rest of the time. In the present research, we tested the hypothesis that if the results of the choice are delayed, pigeons will choose less suboptimally. We tested this hypothesis by forcing pigeons to wait following their choice, requiring them to complete a fixed-interval 20-s schedule prior to receiving the signals for reinforcement. In Experiment 1, we gave the pigeons a choice between (a) a 50% chance of receiving a signal for reinforcement or a 50% chance of receiving a signal for the absence of reinforcement and (b) a 100% chance of receiving a signal for reinforcement. When the signal for reinforcement was delayed, most of the pigeons chose optimally. When it was not delayed, most of the pigeons chose suboptimally. In Experiment 2, we gave the pigeons a choice between (a) a 25% chance of receiving a signal for reinforcement or a 75% chance of receiving a signal for nonreinforcement and (b) a 100% chance of receiving an unreliable signal for reinforcement (predicting reinforcement 75% of the time). When the signal was not delayed, the pigeons showed a strong tendency to choose suboptimally but they chose suboptimally much less when the signal was delayed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The field of comparative cognition has been largely concerned with the degree to which animals have analogs of the cognitive capacities of humans (e.g., imitation, categorization), but recently attention has been directed to behavior that is judged to be biased or suboptimal. We and some of our colleagues have studied several of these and have found that pigeons too show similar paradoxical behaviors. In the present review I will discuss three of these behaviors: sunk cost, justification of effort, and unskilled gambling. Sunk cost is the tendency to decide to spend more on a losing project because of the amount already invested. Pigeons show similar effects even when there is no ambiguity about the results of continuing versus changing alternatives. Justification of effort is the added value one often gives to a reward based on the effort exerted to obtain it. Pigeons too prefer stimuli that signal outcomes that they have had to work harder to obtain. Humans engage in unskilled gambling, like lotteries and slot machines, in which the return is typically less than the investment. And pigeons show a similar tendency to choose a low-probability, high-payoff alternative (gamble) over a more optimal, high-probability, low-payoff alternative. The fact that animals such as pigeons show behavior thought to be unique to humans suggests that the basis for such behaviors is not likely to result from culture or social mechanisms and may have basic behavioral origins. [ABSTRACT FROM AUTHOR]

It is well known that when humans are given a choice between two options, their preference is affected by the presence of a third. Generally, there is an increase in preference for the option closer to the third. We show that a shift in preference in the direction away from the third option can occur in animals. We gave pigeons a choice between A, reinforcement following 10 pecks and a 0.5-s delay, and B, reinforcement following 5 pecks and a 1.5-s delay. Once stable preferences were established, we introduced a third stimulus, less preferred than the other two: C, reinforcement following 20 pecks and a 0.5-s delay or D, reinforcement following 5 pecks and a 4.5-s delay. We found that pigeons presented with C showed an increased preference for B, whereas pigeons presented with D showed an increased preference for A. Our results were consistent with the similarity or attentional hypothesis, which suggests that the third option should interfere with the option more similar to it or would draw attention to the less preferred component of the third option and generalize to the option more similar to it. Possible accounts for the differences in outcomes are suggested. [ABSTRACT FROM AUTHOR]

Highlights: [•] A pigeon model of human gambling behavior. [•] As with human gambling losses play less of a role than they should. [•] As with human gambling low frequency of wins plays less of a role than it should. [Copyright &y& Elsevier]

Justification of effort by humans is a form of reducing cognitive dissonance by enhancing the value of rewards when they are more difficult to obtain. Presumably, assigning greater value to rewards provides justification for the greater effort needed to obtain them. We have found such effects in adult humans and children with a highly controlled laboratory task. More importantly, under various conditions we have found similar effects in pigeons, animals not typically thought to need to justify their behavior to themselves or others. To account for these results, we have proposed a mechanism based on within-trial contrast between the end of the effort and the reinforcement (or the signal for reinforcement) that follows. This model predicts that any relatively aversive event can serve to enhance the value of the reward that follows it, simply through the contrast between those two events. In support of this general model, we have found this effect in pigeons when the prior event consists of: (a) more rather than less effort (pecking), (b) a long rather than a short delay, and (c) the absence of food rather than food. We also show that within-trial contrast can occur in the absence of relative delay reduction theory. Contrast of this kind may also play a role in other social psychological phenomena that have been interpreted in terms of cognitive dissonance. [ABSTRACT FROM AUTHOR]

The sunk cost effect involves the bias to stay with an alternative because one has already invested resources, even when there is a better alternative available. In a series of experiments, at various points during a 30-peck requirement. pigeons (Columba livia) could choose between completing the response requirement (at a different location in Experiment 1 or the same location in Experiments 3 and 4) and switching to a constant number of pecks. In three experiments, the pigeons showed a bias to complete the pecks already started, even when that required more pecking. We also demonstrated that the bias depended on the initial investment and was not produced merely because the pigeons preferred a variable alternative over a fixed alternative. The deviation from optimal choice suggests that pigeons show a bias similar to the sunk cost effect in humans. [ABSTRACT FROM AUTHOR]

Abstract: Pigeons show a preference for an alternative that provides them with discriminative stimuli (sometimes a stimulus that predicts reinforcement and at other times a stimulus that predicts the absence of reinforcement) over an alternative that provides them with nondiscriminative stimuli, even if the nondiscriminative stimulus alternative is associated with 2.5 times as much reinforcement (). In Experiment 1 we found that the delay to reinforcement associated with the nondiscriminative stimuli could be reduced by almost one half before the pigeons were indifferent between the two alternatives. In Experiment 2 we tested the hypothesis that the preference for the discriminative stimulus alternative resulted from the fact that, like humans, the pigeons were attracted by the stimulus that consistently predicted reinforcement (the Allais paradox). When the probability of reinforcement associated with the discriminative stimulus that predicted reinforcement was reduced from 100% to 80% the pigeons still showed a strong preference for the discriminative stimulus alternative. Thus, under these conditions, the Allais paradox cannot account for the sub-optimal choice behavior shown by pigeons. Instead we propose that sub-optimal choice results from positive contrast between the low expectation of reinforcement associated with the discriminative stimulus alternative and the much higher obtained reinforcement when the stimulus associated with reinforcement appears. We propose that similar processes can account for sub-optimal gambling behavior by humans. [Copyright &y& Elsevier]

Abstract: Pigeons prefer a positive discriminative (S+) stimulus that follows a less preferred event (a large number of required responses, a longer delay, or the absence of food) over a different S+ with a similar history of reinforcement that follows a more preferred event (a single required response, no delay, or food). We proposed that this phenomenon results from contrast (referred to as within-trial contrast) between the less preferred initial event and the signal for reinforcement. Delay reduction theory () can account for these results by proposing that the less preferred initial event lengthens the duration of the trial, thereby allowing the S+ stimulus to occur later in the trial and thus become a better predictor of reinforcement. In the present experiments, we further explored this effect. In Experiment 1, we controlled for trial duration by using a fixed ratio response (30 pecks) as one initial event and the absence of pecking for the same duration as the other initial event (0 pecks). The pigeons showed a reliable preference for the positive stimulus that followed the least preferred initial event. In Experiment 2, we controlled for trial duration by using 30 pecks as one initial event and 1 peck followed by a delay that matched the duration of the preceding 30-peck trial. (Group Time Same). For Group Time Different, there was no delay following the 1-peck initial event. For Group Time Same, preference for the initial event negatively predicted the pigeons’ preference for the S+ stimulus that followed, supporting the contrast account. A somewhat greater preference for the discriminative stimulus that followed the least preferred initial event was found for Group Time Different suggesting that in addition to contrast, delay reduction also may play a small role. However, the greater initial-event preference found for Group Time Different suggests that contrast can account for the group difference as well. [Copyright &y& Elsevier]

Numerical competence has been studied in animals under a variety of conditions, but only a few experiments have reported animals' ability to detect absolute number. Capaldi and Miller (1988) tested rats' ability to detect absolute number by using biologically important events-the number of remforced runs followed by a nonreinforced run-and found that the rats ran significantly slower on the nonreinforced run. In the present experiments, we used a similar procedure. Pigeons were given a sequence of trials in which responding on the first three trials ended in reinforcement but responding on the fourth trial did not (RRRN). When the response requirement on each trial was a single peck (Experiment 1), we found no significant increase in latency to peck on the fourth trial. When the response requirement was increased to 10 pecks (Experiment 2), however, the time to complete the peck requirement was significantly longer on the nonreinforced trial than on the reinforced trials. Tests for control by time, number of responses, and amount of food consumed indicated that the pigeons were using primarily the number of reinforcements obtained in each sequence as a cue for nonreinforcement. This procedure represents a sensitive and efficient method for studying numerical competence in animals. [ABSTRACT FROM AUTHOR]

Using a radial maze analog task, T. R. Zentall, J. N. Steirn, and P. Jackson-Smith (1990) found evidence that when a delay was interpolated early in a trial, pigeons coded locations retrospectively, but when the delay was interpolated late in the trial, they coded locations prospectively (support for a dual coding hypothesis). In Experiment 1 of the present study, the authors replicated the original finding of dual coding. In Experiments 2 and 3, they used a 2-alternative test procedure that does not require the assumption that pigeons' choice criterion, which changes over the course of the trial, is the same on delay and control trials. Under these conditions, the pigeons no longer showed evidence for dual coding. Instead, there was some evidence that they showed prospective coding, but a more parsimonious account of the results may be that the delay produced a relatively constant decrement in performance at all points of delay interpolation. The original finding of dual coding by Zentall et al. might have been biased by more impulsive choices early in control trials but not in delay trials and by a more stringent choice criterion late in delay trials. [ABSTRACT FROM AUTHOR]

Clement, Feltus, Kaiser, and Zentall (2000) found that when pigeons have to work to obtain a discriminative stimulus that is followed by reinforcement, they prefer a discriminative stimulus that requires greater effort over one that requires less effort. The authors suggested that such a preference results from the greater change in hedonic value that occurs between the more aversive event and the onset of the stimulus that signals reinforcement, a contrast effect. It was hypothesized that any stimulus that follows a relatively more aversive event would be preferred over a stimulus that follows a relatively less aversive event. In the present experiment, the authors tested the counterintuitive prediction of that theory, that pigeons should prefer a discriminative stimulus that follows the absence of reinforcement over a discriminative stimulus that follows reinforcement. Results supported the theory. [ABSTRACT FROM AUTHOR]

The bidirectional control procedure was used to determine whether pigeons (Columba livia) would imitate a demonstrator that pushed a sliding screen for food. One group of observers saw a trained demonstrator push a sliding screen door with its beak (imitation group), whereas 2 other groups watched the screen move independently (possibly learning how the environment works) with a conspecific either present (affordance learning with social facilitation) or absent (affordance learning alone). A 4th group could not see the screen being pushed (sound and odor control). Imitation was evidenced by the finding that pigeons that saw a demonstrator push the screen made a higher proportion of matching screen pushes than observers in 2 appropriate control conditions. Further, observers that watched a screen move without a demonstrator present made a significantly higher proportion of matching screen pushes than would be expected by chance. Thus, these pigeons were capable of affordance learning. [ABSTRACT FROM AUTHOR]

In the present experiments, the 2-action method was used to determine whether pigeons could learn to imitate a conditional discrimination. Demonstrator pigeons (Columba livia) stepped on a treadle in the presence of 1 light and pecked at the treadle in the presence of another light. Demonstration did not seem to affect acquisition of the conditional discrimination (Experiment 1) but did facilitate its reversal of the conditional discrimination (Experiments 2 and 3). The results suggest that pigeons are not only able to learn a specific behavior by observing another pigeon, but they can also learn under which circumstances to perform that behavior. The results have implications for proposed mechanisms of imitation in animals. [ABSTRACT FROM AUTHOR]

Presents an experiment to assess how pigeons estimate the probability of correct conditioned response when sample probabilities differ from the comparison stimuli. Presence of divergent retention functions by the delay-induced loss of sample strength; Association of the conditional probabilities with the choice of comparison stimuli; Selection of the comparison associated with the more frequently presented sample.

Focuses on divergent choose-absence retention functions typically found following presence/absence-sample matching in pigeon. Control of comparison choice; Role of differential-sample responding in the divergent retention function in pigeons; Development of single-code/default coding strategy in pigeons; Divergent choose-absence retention function.

Studies whether pigeons are capable of flexible cognitively efficient learning. Development of a single-code/default coding strategy in pigeons; Study of animal cognition or animals' ability to develop active strategies for solving novel problems.

Examines the influence of positive (S+) and negative (S-) stimulus in a simultaneous discrimination experiments involving pigeons. Influence of the presence of S- on the value of S+; Value transfers from S+ to S-; Instances when the demonstration of the contrast between S+ and S- are possible.

Examines how the trace-strength theory of timing and memory for event duration can account for pigeons' bias to `choose short' when retention intervals are introduced and to `choose long' in a fixed retention interval. Stimulus generalization resulting in an effect that has been attributed to memory loss; Effects of retention interval on memory loss.

Discusses the two-process interpretation of the differential outcome effect (DOE) in pigeons. Presumed associations involved in standard differential outcome procedure; Control for differential-sample responding; DOE in acquisition; Differential response-outcome associations.

Examines the source of directed forgetting in delayed matching in pigeons. Manipulation of forget-cue trials in training; Reinforced responding following forget cues; Elimination of performance deficits on forget-cue probe trials.

Examines the role of differential sample responding in the differential outcomes effect involving delayed matching by pigeons. Effect of using food versus no food as differential outcomes; Results suggesting that differential outcomes exert their effect independently of differential sample responding.

Proposes a value transfer theory to account for transitive inference effects in which following training on several simultaneous discriminations, pigeons show preferences. Review of related literature; Characteristics of subjects in study; Training methods.

Focuses on three experiments which support the contention that retrieval failure does not account for the element superiority effect (ESE), with regards to pigeons. Unique nature of a pigeon's ability to retrieve the relevant element; Definition of ESE; Description of four accounts of ESE; Factor to which ESE can be attributed to; Focus of each experiment; What the findings of the experiments indicate.

Assesses the role of retention interval keypecking on delayed matching accuracy for directed forgetting in pigeons. Results of memory tests for cues R-remember, F-forget, A-ambiguous; Pecking behavior of pigeons in the substitution group and the omission group; Relationship between delay cue-pecking and matching performance.

Determines whether differential outcome expectancies alone could control comparison choice and examines the contribution of differential sample responding to the differential-outcomes effect (DOE) in pigeons. Acquisition of the training phases; Transfer phase.

Examines the form of the common codes that develop in many-to-one delayed matching-to-sample (MTO DMTS) in pigeons. Use of hue samples; Rate of the acquisition of DMTS; Accounts of the hue-sample asymmetry.

Studies the distinction between the backward-association and proactive interference accounts of the short-delay comparison bias found in pigeons with food- versus no-food-sample delayed conditional discriminations. Approaches to backward conditioning; Evidence for asymmetry in the delay functions; Significance of reducing the probability of reinforcement.

Discusses the common coding training of pigeons. Many-to-one (MTO) delayed matching with individual comparison stimuli associations; Role of identity relations in MTO common coding; Performance significantly more accurate due to stimulus association with the same comparison; Common coding of samples sharing common comparison associations.

Investigates the interchangeability of comparisons matched to a common sample stimulus among pigeons. Transfer effects; Directionality of training; Production of emergent stimulus relation in pigeons' matching to sample.

Studies emergent relations in the formation of stimulus classes by pigeons. Reflexivity; Symmetry; Transitivity; Identity matching to stimuli; Substitution for conditional stimuli in a matching task; Successive hue discrimination.

Examines pigeons' behavior when presented with a radial-arm-maze analog task involving five response keys in one of four spatial arrangements. Acquisition; Delay; Arrangements; Overall performance.

Presents information on a study which examined value transfer during simultaneous discrimination training by pigeons. Description of methodology used in the study; Investigation of the mechanism underlying value transfer between simultaneously presented stimuli; Findings of the study.

Studies demonstrate imitative learning among pigeons. Reference to Zentall, Sutton, and Sherburne (1996); Methodology used in the study; Number of subjects in the study; Results of the study.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Research has shown that pigeons given a simultaneous visually based discrimination reversal, in which a single reversal occurs at the midpoint of each session, consistently show anticipation prior to the reversal as well as perseveration after the reversal, suggesting that they use a less effective cue (time or trial number into the session) than what would be optimal to maximize reinforcement (local feedback from the most recent trials). In the present research, pigeons (Columba livia) and rats (Rattus norvegicus) were tested with a simultaneous spatial discrimination midsession reversal. Pigeons showed remarkably similar errors in anticipation and perseveration as with visual stimuli, thereby continuing to show the suboptimal use of time as a cue, whereas rats showed no anticipatory errors and very few perseverative errors, suggesting that they used local feedback as a cue, thus more nearly optimizing reinforcement. To further test the rats' flexibility, they were then tested with a variable point of reversal and then with multiple points of reversal within a session. Results showed that the rats effectively maximized reinforcement by developing an approximation to a win-stay/lose-shift rule. The greater efficiency shown by rats with this task suggests that they are better able to use the feedback from their preceding choice as the basis of their future choice. The difference in cue preference further suggests a qualitative difference in acquisition of the midsession reversal task between pigeons and rats. [ABSTRACT FROM AUTHOR]

Abstract: There is evidence that pigeons prefer conditioned reinforcers that are preceded by greater effort over those that are preceded by less effort (an effect that has been attributed to within-trial contrast). In past research the probability of reinforcement for correct choice of the conditioned reinforcer has been 100%, however, the high level of reinforcement for both alternatives in training may result in a performance ceiling when choice between those alternatives is provided on test trials. In the present study we tested this hypothesis by including a group for which the probability of reinforcement in training was only 50%. Pigeons were trained on two simultaneous discriminations, one that was preceded by a 30peck requirement the other by a single peck requirement. On test trials, we found a significant preference for the S+ that required the greater effort in training for pigeons trained with 100% and a small but nonsignificant effect for pigeons trained with 50% reinforcement. Although the hypothesis that the within-trial contrast effect was constrained by a performance ceiling was not confirmed, we did find a reliable within-trial contrast effect with 100% reinforcement. [Copyright &y& Elsevier]