Delay of gratification and delay maintenance by rhesus macaques (Macaca mulatta)

The authors tested the self-control of rhesus macaques by assessing if they could refrain from reaching into a food container to maximize the accumulation of sequentially delivered food items (a delay-maintenance task). Three different versions of the task varied the quantity and quality of available food items. In the first 2 versions, food items accumulated across the length of the trial until a monkey consumed the items. In the 3rd task, a single less-preferred food item preceded a single more-preferred food item. Some monkeys delayed gratification even with relatively long delays between deliveries of items. However, the data suggested that self-control, in the majority of tested individuals, was not significantly different across different task versions and that self-control by macaques was not as prevalent in these tasks as it is in chimpanzees and human children.     

How suboptimal is suboptimal choice?

In a frequently used suboptimal‐choice procedure pigeons choose between an alternative that delivers three food pellets with p = 1.0 and an alternative that delivers ten pellets with p = 0.2. Because pigeons reliably choose the probabilistic (suboptimal) alternative, the procedure has been proposed as a nonhuman analog of human gambling. The present experiments were conducted to evaluate two potential threats to the validity of this procedure. Experiments 1 and 2 evaluated if pigeons obtained food at a lower unit price (i.e., pecks per pellet) on the suboptimal alternative than on the optimal alternative. When pigeons worked under this suboptimal procedure they all preferred the suboptimal alternative despite some pigeons paying a higher price for food on that alternative. In Experiment 2, when the unit price ratio more closely approximated the inverse of the expected value ratio, pigeons continued to prefer the suboptimal alternative despite its economic suboptimality. Experiment 3 evaluated if, in accord with the string‐theory of gambling, the valuation of the suboptimal alternative was increased when pigeons misattributed a subset of the suboptimal no‐food trials to the optimal alternative. When trial sequences were arranged to minimize these possible attribution errors, pigeons still preferred the suboptimal alternative. These data remove two threats to the validity of the suboptimal choice procedure; threats that would have suggested that suboptimal choice reflects economic maximization.     

Preference Assessment for Dimensions of Reinforcement to Inform Token Economies Targeting Problem Behavior

The purpose of the current two-experiment study was to examine the use of a preference assessment for dimensions of reinforcement to inform an effective token economy arrangement. Three participants diagnosed with developmental disabilities who engaged in negatively reinforced problem behavior participated in this study. During Experiment 1, a preference assessment for four dimensions of reinforcement (i.e., quality, immediacy, magnitude, and rate) occurred to inform a more- and less-preferred token economy arrangement. During Experiment 2, a treatment evaluation compared these two token economy arrangements. Results for all three participants showed lower rates of problem behavior under the more-preferred token economy arrangement compared to the less-preferred token economy arrangement. Rates of task completion were higher under the more-preferred token economy arrangement for one of the three participants. Results are discussed in terms of their practical implications for clinicians and educators implementing token economies to manage problem behavior.     

Social comparison mediates chimpanzees’ responses to loss,not frustration

Why do chimpanzees react when their partner gets a better deal than them? Do they note the inequity or do their responses reflect frustration in response to unattainable rewards? To tease apart inequity and contrast, we tested chimpanzees in a series of conditions that created loss through individual contrast, through inequity, or by both. Chimpanzees were tested in four social and two individual conditions in which they received food rewards in return for exchanging tokens with an experimenter. In conditions designed to create individual contrast, after completing an exchange, the chimpanzees were given a relatively less-preferred reward than the one they were previously shown. The chimpanzees’ willingness to accept the less-preferred rewards was independent of previously offered foods in both the social and individual conditions. In conditions that created frustration through inequity, subjects were given a less-preferred reward than the one received by their partner, but not in relation to the reward they were previously offered. In a social context, females were more likely to refuse to participate when they received a less-preferred reward than their partner (disadvantageous inequity), than when they received a more-preferred reward (advantageous inequity). Specifically, the females’ refusals were typified by refusals to exchange tokens rather than refusals to accept food rewards. Males showed no difference in their responses to inequity or individual contrast. These results support previous evidence that some chimpanzees’ responses to inequity are mediated more strongly by what others receive than by frustration effects.     

Recognition-based inference: When is less more in the real world?

Common wisdom tells us that more information can only help and never hurt. Goldstein and Gigerenzer (2002) highlighted an instance violating this intuition. Specifically, in an analysis of their recognition heuristic, they found a counterintuitive less-is-more effect in inference: An individual recognizing fewer objects than another individual can, nevertheless, make more accurate inferences. Goldstein and Gigerenzer emphasized that a sufficient condition for this effect is that the recognition validity be higher than the knowledge validity, assuming that the validities are uncorrelated with the number of recognized objects, n. But how is the occurrence of the less-is-more effect affected when this independence assumption is violated? I show that validity dependencies (i.e., correlations of the validities with n) abound in empirical data sets, and I demonstrate by computer simulations that these dependencies often have a strong limiting effect on the less-is-more effect. Moreover, I discuss what cognitive (e.g., memory) and ecological (e.g., distribution of the criterion variable, environmental frequencies) factors can give rise to a dependency of the recognition validity on the number of recognized objects. Supplemental materials may be downloaded from http://pbr.psychonomic-journals.org/content/supplemental.     

Pigeons' discrimination of Michotte's launching effect

We trained four pigeons to discriminate a Michotte launching animation from three other animations using a go/no-go task. The pigeons received food for pecking at one of the animations, but not for pecking at the others. The four animations featured two types of interactions among objects: causal (direct launching) and noncausal (delayed, distal, and distal & delayed). Two pigeons were reinforced for pecking at the causal interaction, but not at the noncausal interactions; two other pigeons were reinforced for pecking at the distal & delayed interaction, but not at the other interactions. Both discriminations proved difficult for the pigeons to master; later tests suggested that the pigeons often learned the discriminations by attending to subtle stimulus properties other than the intended ones.     

The Δ–∑ hypothesis: How contrast and reinforcement rate combine to generate suboptimal choice

When given a choice between two alternatives, each offering food after the same delay with different but signaled probabilities, pigeons often prefer the low probability alternative. This preference is surprising because pigeons fail to maximize the rate of food intake; they exhibit a suboptimal preference. We advance a new explanation, the Δ–∑ hypothesis, in which the difference in probability of reinforcement within terminal links (Δ) and the overall reinforcement probability rate of each alternative (∑) are the key variables responsible for such suboptimal preference. We tested the Δ–∑ hypothesis in two experiments. In Experiment 1, we manipulated the Δs while maintaining constant all other parameters of the task, in particular the ∑s. We predicted a preference for the alternative with the larger Δ. In Experiment 2, we examined the effect of the overall reinforcement probabilities, the ∑s, while maintaining constant all other parameters of the task, in particular the Δs. We predicted a preference for the larger ∑. The results of both experiments support the Δ–∑ hypothesis.     

The role of similarity in inattentional blindness: Selective enhancement,selective suppression,or both?†

When people selectively pay attention to one set of objects and ignore another, unexpected stimuli often go unnoticed. Noticing rates are higher when the unexpected object matches the features of the attended items and lower when it matches those of the ignored items. No prior studies have fully disentangled these aspects of similarity; in previous work, the unexpected object fell on a continuum between the attended and ignored objects, so increasing the similarity to one set of objects necessarily decreased it to the other. We designed an inattentional blindness task in which we held similarity to the attended set constant and varied it with respect only to the ignored set, or vice versa. In Experiment 1, objects that were more similar to the attended set were noticed more often and objects that were more similar to the ignored set were noticed less often. Experiment 2, using a different set of unexpected objects, replicated the result that similarity to the ignored set affected noticing, but showed no effect of similarity to the attended set. In both experiments, the pattern of noticing rates differed for similarity with respect to the attended and ignored items, suggesting that suppression of ignored objects functions independently of enhancement of attended objects.     

Typical delay determines waiting time on periodic-food schedules: Static and dynamic tests

Pigeons and other animals soon learn to wait (pause) after food delivery on periodic-food schedules before resuming the food-rewarded response. Under most conditions the steady-state duration of the average waiting time, t, is a linear function of the typical interfood interval. We describe three experiments designed to explore the limits of this process. In all experiments, t was associated with one key color and the subsequent food delay, T, with another. In the first experiment, we compared the relation between t (waiting time) and T (food delay) under two conditions: when T was held constant, and when T was an inverse function of t. The pigeons could maximize the rate of food delivery under the first condition by setting t to a consistently short value; optimal behavior under the second condition required a linear relation with unit slope between t and T. Despite this difference in optimal policy, the pigeons in both cases showed the same linear relation, with slope less than one, between t and T. This result was confirmed in a second parametric experiment that added a third condition, in which T + t was held constant. Linear waiting appears to be an obligatory rule for pigeons. In a third experiment we arranged for a multiplicative relation between t and T (positive feedback), and produced either very short or very long waiting times as predicted by a quasi-dynamic model in which waiting time is strongly determined by the just-preceding food delay.     

The use of recognition in group decision-making

Goldstein and Gigerenzer (2002) [Models of ecological rationality: The recognition heuristic. Psychological Review, 109 (1), 75-90] found evidence for the use of the recognition heuristic. For example, if an individual recognizes only one of two cities, they tend to infer that the recognized city has a larger population. A prediction that follows is that of the less-is-more effect: Recognizing fewer cities leads, under certain conditions, to more accurate inferences than recognizing more cities. We extend the recognition heuristic to group decision-making by developing majority and lexicographic models of how recognition information is used by groups. We formally show when the less-is-more effect is predicted in groups and we present a study where three-member groups performed the population comparison task. Several aspects of our data indicate that members who can use the recognition heuristic are, not in all but in most cases, more influential in the group decision process than members who cannot use the heuristic. We also observed the less-is-more effect and found that models assuming that members who can use the recognition heuristic are more influential better predict when the effect occurs.     

Animacy increases second target reporting in a rapid serial visual presentation task

Attentional blink occurs when two target items, T1 and T2, are presented within brief moments of each other in a series of rapidly presented items and participants fail to report T2. The purpose of the present study was to examine the effect of characteristics of T2 on T2 reporting. Participants (N = 67) completed 4 blocks of 40 trials. Each trial consisted of 15 images, two of which were designated as T1 and T2. T2 was manipulated in three ways: animacy (animate or inanimate), threat (threatening or nonthreatening), and lag (200 ms or 400 ms after T1). The results indicated that more T2s were reported at the longer lag and that animate objects were reported more often than inanimate objects at both lags. Threat did not have a significant effect on T2 reporting although it interacted with lag: threatening objects were reported more frequently than nonthreatening objects at lag 2 but this trend reversed at lag 4. The results were consistent with the animate monitoring hypothesis, which claims that animate objects, because of their importance in ancestral environments, attract attention more easily than inanimate objects. Animate objects appear to capture attention more easily than inanimate objects as second targets in a rapid serial visual presentation task. This result is similar to animacy advantages reported with other attention tasks and with memory tasks.     

Transfer from “edible” categorization training to feeding behavior in pigeons (Columba livia)1

Abstract: We investigated a transfer from an operant experimental situation to a feeding situation in pigeons using real objects as stimuli. Four pigeons were trained in an operant box to categorize familiar edible items as positives and inedible items as negatives with a go/no‐go procedure. Next, two pairs of unfamiliar edible items were added as stimuli. One of the paired stimuli was arbitrarily assigned as positive and the other as negative. We tested the subjects in their home cages to see whether they would feed on the items they were trained to categorize as positives. In three of the six cases in which categorization training was successful, they continued to peck the positive items. This result suggests that the pigeons transfer what they learned in the operant training situation to the feeding situation.     

The Monty Hall dilemma in pigeons: Effect of investment in initial choice

In the Monty Hall dilemma, humans are initially given a choice among three alternatives, one of which has a hidden prize. After choosing, but before it is revealed whether they have won the prize, they are shown that one of the remaining alternatives does not have the prize. They are then asked whether they want to stay with their original choice or switch to the remaining alternative. Although switching results in obtaining the prize two thirds of the time, humans consistently fail to adopt the optimal strategy of switching even after considerable training. Interestingly, there is evidence that pigeons show more optimal switching performance with this task than humans. Because humans often view even random choices already made as being more valuable than choices not made, we reasoned that if pigeons made a greater investment, it might produce an endowment or ownership effect resulting in more human-like suboptimal performance. On the other hand, the greater investment in the initial choice by the pigeons might facilitate switching behavior by helping them to better discriminate their staying versus switching behavior. In Experiment 1, we examined the effect of requiring pigeons to make a greater investment in their initial choice (20 pecks rather than the usual 1 peck). We found that the increased response requirement facilitated acquisition of the switching response. In Experiment 2, we showed that facilitation of switching due to the increased response requirement did not result from extinction of responding to the initially chosen location.     

Reversed better-than-average effect in direct comparisons of nonsocial stimuli depends on the set size

Studies on direct comparative judgments typically show that, for items that are positively evaluated, a single item randomly drawn from a larger set of similar items tends to be judged as better than average (the BTA effect). However, Windschitl, Conybeare, and Krizan (2008) demonstrated that, under timing conditions that do not favor focusing attention on the single item, the reversal of the BTA effect occurs. We report two experiments showing that the magnitude of the reversed BTA effect increases as a function of the size of a multiitem referent with which a single item target is compared. Specifically, in direct comparative judgments of the attractiveness of positively evaluated objects (nice-looking cloth buttons, attractive buildings, or cupcakes), underestimation of the attractiveness of singletons, as compared with a multiitem set (reversed BTA effect), increased with the increased set size. Analysis of absolute judgments obtained for singletons and for small and large multiitem sets suggests that, for attractive stimuli, both the reversed BTA effect in comparative judgments and its sensitivity to set size occur as a result of a positive relationship between set size and perceived attractiveness in absolute judgments.     

Summation of symbols by pigeons (Columba livia): the importance of number and mass of reward items

In each of 3 experiments, different sets of 4 pigeons (Columba livia) were trained to discriminate between 2 visual symbols that covered wells containing food items that varied in number, mass, or both. In Experiment 1, the symbols were associated with 0, 1, 3, 5, 7, or 9 pieces of grain reward. The pigeons learned to choose the symbol corresponding to the larger reward, and on summation tests, they chose the pair of symbols that summed to the larger total reward. When number of food pellets was varied but mass of reward was held constant in Experiment 2, preference for the larger number symbols failed to appear. When number was held constant and mass was varied in Experiment 3, the pigeons showed a clear preference for the larger mass symbols on single-symbol and summation tests. These findings show that pigeons summate the value of symbols and are more likely to represent symbols by mass of food reward than by number of food items.     

Hungry pigeons make suboptimal choices, less hungry pigeons do not

Hungry animals will often choose suboptimally by being attracted to reliable signals for food that occur infrequently (they gamble) over less reliable signals for food that occur more often. That is, pigeons prefer an option that 50?% of the time provides them with a reliable signal for the appearance of food but 50?% of the time provides them with a reliable signal for the absence of food (overall 50?% reinforcement) over an alternative that always provides them with a signal for the appearance of food 75?% of the time (overall 75?% reinforcement). The pigeons appear to choose impulsively for the possibility of obtaining the reliable signal for reinforcement. There is evidence that greater hunger is associated with greater impulsivity. We tested the hypothesis that if the pigeons were less hungry, they would be less impulsive and, thus, would choose more optimally (i.e., on the basis of the overall probability of reinforcement). We found that hungry pigeons choose the 50?% reinforcement alternative suboptimally but less hungry pigeons prefer the more optimal 75?% reinforcement. Paradoxically, pigeons that needed the food more received less of it. These findings have implications for how level of motivation may also affect human suboptimal choice (e.g., purchase of lottery tickets and playing slot machines).     

Rhesus monkeys (Macaca mulatta) demonstrate robust memory for what and where,but not when,in an open-field test of memory

We adapted a paradigm developed by Clayton and Dickinson (1998), who demonstrated memory for what, where, and when in scrub jays, for use with rhesus monkeys. In the study phase of each trial, monkeys found a preferred and a less-preferred food reward in a trial-unique array of three locations in a large room. After 1 h, monkeys returned to the test room, where they found foods placed as during study. Twenty-five hours after the study phase monkeys again searched the room, but now the preferred food was replaced with a distasteful food remnant, while the less-preferred food was still present. Although monkeys remembered the locations of the foods for up to 25 h, they did not learn that the preferred food was available after the short, but not after the long delay. Thus, monkeys demonstrated long-term memory for the type and location of food but failed to demonstrate sensitivity to when they acquired that knowledge.     

Natural choice in chimpanzees (Pan troglodytes): Perceptual and temporal effects on selective value

In three experiments, four chimpanzees made choices between two visible food options to assess the validity of the selective value effect (the assignment of value to only the most preferred type of food presented in a comparison). In Experiment 1, we established that all chimpanzees preferred single banana pieces to single apple pieces before presenting the critical test. In this test two chimpanzees preferred a mix of one banana piece and one apple piece to a single banana piece when both banana pieces were approximately the same size, but two chimpanzees were indifferent between the two options, exhibiting the selective value effect. In Experiment 2, when the banana pieces in both options were more closely equated in size, the chimpanzees were biased to choose the single banana piece over the mixed array even though this was the smaller total amount of food. However, in Experiment 3, when we introduced longer intervals between each trial, the chimpanzees preferred the mixed set and thus the larger total amount of food. The results demonstrate that only some chimpanzees exhibit the choice pattern indicative of the selective value effect, and they do so only when item size is not carefully controlled and trials are presented quickly in succession. Thus, the behavior pattern originally labeled the selective value effect may actually be explained by a combination of chimpanzees’ sensitivity to small differences in preferred food amount and chimpanzees tendency to avoid less preferred foods that would delay the acquisition of further preferred food items.     

DISCOUNTING OF DELAYED FOOD REWARDS IN PIGEONS AND RATS: IS THERE A MAGNITUDE EFFECT?

Temporal discounting refers to the decrease in the present, subjective value of a reward as the time to its receipt increases. Results from humans have shown that a hyperbola-like function describes the form of the discounting function when choices involve hypothetical monetary rewards. In addition, magnitude effects have been reported in which smaller reward amounts are discounted more steeply than larger amounts. The present research examines the cross-species generality of these findings using real rewards, namely food pellets, with both pigeons and rats. As with humans, an adjusting amount procedure was used to estimate the amount of immediate reward judged equal in value to a delayed reward. Different amounts of delayed food rewards (ranging from 5 to 32 pellets in pigeons and from 5 to 20 pellets in rats) were studied at delays varying from 1 s to 32 s. A simple hyperbola, similar to the hyperbola-like mathematical function that describes the discounting of hypothetical monetary rewards in humans, described the discounting of food rewards in both pigeons and rats. These results extend the generality of the mathematical model of discounting. Rates of discounting delayed food rewards were higher for pigeons than for rats. Unlike humans, however, neither pigeons nor rats showed a reliable magnitude effect: Rate of discounting did not vary systematically as a function of the amount of the delayed reward.     

Complex conditional control by pigeons in a continuous virtual environment

We tested two pigeons in a continuously streaming digital environment. Using animation software that constantly presented a dynamic, three‐dimensional (3D) environment, the animals were tested with a conditional object identification task. The correct object at a given time depended on the virtual context currently streaming in front of the pigeon. Pigeons were required to accurately peck correct target objects in the environment for food reward, while suppressing any pecks to intermixed distractor objects which delayed the next object's presentation. Experiment 1 established that the pigeons’ discrimination of two objects could be controlled by the surface material of the digital terrain. Experiment 2 established that the pigeons’ discrimination of four objects could be conjunctively controlled by both the surface material and topography of the streaming environment. These experiments indicate that pigeons can simultaneously process and use at least two context cues from a streaming environment to control their identification behavior of passing objects. These results add to the promise of testing interactive digital environments with animals to advance our understanding of cognition and behavior.