Capuchin monkeys (Cebus apella) let lesser rewards pass them by to get better rewards

Self-control is defined as foregoing an immediate reward to gain a larger delayed reward. Methods used to test self-control comparatively include inter-temporal choice tasks, delay of gratification tasks, and accumulation tasks. To date, capuchin monkeys have shown different levels of self-control across tasks. This study introduced a new task that could be used comparatively to measure self-control in an intuitive context that involved responses that required no explicit training. Capuchin monkeys (Cebus apella) were given a choice between two food items that were presented on a mechanized, revolving tray that moved those foods sequentially toward the monkeys. A monkey could grab the first item or wait for the second, but was only allowed one item. Most monkeys in the study waited for a more highly preferred food item or a larger amount of the same food item when those came later, and they inhibited the prepotent response to grab food by not reaching out to take less-preferred foods or smaller amounts of food that passed directly in front of them first. These data confirm that the mechanisms necessary for self-control are present in capuchin monkeys and indicate that the methodology can be useful for broader comparative assessments of self-control.     

Chimpanzees (Pan troglodytes) transfer tokens repeatedly with a partner to accumulate rewards in a self-control task

There has been extensive research investigating self-control in humans and nonhuman animals, yet we know surprisingly little about how one’s social environment influences self-control. The present study examined the self-control of chimpanzees in a task that required active engagement with conspecifics. The task consisted of transferring a token back and forth with a partner animal in order to accumulate food rewards, one item per token transfer. Self-control was required because at any point in the trial, either chimpanzee could obtain their accumulated rewards, but doing so discontinued the food accumulation and ended the trial for both individuals. Chimpanzees readily engaged the task and accumulated the majority of available rewards before ending each trial, and they did so across a number of conditions that varied the identity of the partner, the presence/absence of the experimenter, and the means by which they could obtain rewards. A second experiment examined chimpanzees’ self-control when given the choice between immediately available food items and a potentially larger amount of rewards that could be obtained by engaging the token transfer task with a partner. Chimpanzees were flexible in their decision-making in this test, typically choosing the option representing the largest amount of food, even if it involved delayed accumulation of the rewards via the token transfer task. These results demonstrate that chimpanzees can exhibit self-control in situations involving social interactions, and they encourage further research into this important aspect of the self-control scenario.     

Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance

Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.     

Long-tailed macaques (Macaca fascicularis) understand what conspecifics can see in a competitive situation

Visual perspective taking (VPT), an understanding of what others can see, is a prerequisite for theory of mind (ToM). While VPT in apes is proven, its presence in monkeys is much-debated. Several different paradigms have been developed to test its existence, but all face interpretational problems since results can be explained by simpler cognitive mechanisms than VPT. Therefore, we adjusted one method where two individuals compete for access to food, visible or invisible for the dominant competitor, to preclude cognitively simpler mechanisms. The subordinate long-tailed macaques tested, selected significantly more often the food item invisible than the item visible to the dominant. In most trials, subjects retrieved only one food item and preferred the invisible food item. Surprisingly, they occasionally adopted an alternative strategy to obtain both food items, by first choosing the visible, most at risk food item. Faster animals adopted this strategy proportionally more often than slower ones. Contrary to previous research, our results cannot be explained by simpler cognitive mechanisms, since behavioural reading was prevented by a one-way mirror between the competitor and the food, and accessibility was equal to both food items. This is the first unequivocal evidence of VPT in a monkey species, suggesting that this precursor to ToM is an evolutionarily conserved capacity present in monkeys, apes and humans.     

Does the rose still smell as sweet? Item variability across test forms and revisions

This article examines item stability when the same item appears in different contexts. The 1st section considers the assumptions in classical test theory and item response theory concerning the relationship between the item and the trait it is presumed to measure. The 2nd section presents contextualist challenges to the measurement theory assumptions about item properties and shows the instability of item characteristics across different testing contexts. The 3rd section describes methods for checking the relationship between items and traits. Classical test methods, item response methods, and structural equation methods for assessing item stability are reviewed. The instability of item characteristics across contexts should caution researchers to assess, and not assume, that items operate the same way on different test versions. Item instability also indicates the need for a more detailed understanding of the psychological processes that occur between item and answer.     

Chimpanzees (Pan troglodytes) can wait,when they choose to: a study with the hybrid delay task

Self-control has been studied in nonhuman animals using a variety of tasks. The inter-temporal choice (ITC) task presents choices between smaller–sooner (SS) and larger–later (LL) options. Using food amounts as rewards, this presents two problems: (a) choices of the LL option could either reflect self-control or instead result from animals’ difficulty with pointing to smaller amounts of food; (b) there is no way to verify whether the subjects would not revert their choice for the LL option, if given the opportunity to do so during the ensuing delay. To address these problems, we have recently introduced a new protocol, the hybrid delay task, which combines an initial ITC with a subsequent accumulation phase in which selection of the SS option leads to its immediate delivery, but choice of the LL option then leads to one-by-one presentation of those items that continues only as long as the subject does not eat any of the accumulated items. The choice of the LL option therefore only reflects self-control when the number of items obtained from LL choices during the accumulation phase is higher than what could be received in the SS option. Previous research with capuchin monkeys demonstrated that their apparent self-control responses in the ITC task may have overestimated their general self-control abilities, given their poor performance in the hybrid delay task. Here, chimpanzees instead demonstrated that their choices for the LL option in the ITC phase of the hybrid delay task were confirmed by their ability to sustain long delays during accumulation of LL rewards.     

Time preferences in long-tailed macaques (Macaca fascicularis) and humans (Homo sapiens)

Rosati et al. (Curr Biol 17(19):1663–1668, 2007) found in a self-control test in which choice was between a smaller, immediately delivered food and a larger, delayed food, that chimpanzees preferred the larger reward (self-control); humans, however, preferred the smaller reward (impulsivity). They attributed their results to a species difference in self-control. In Experiment 1, monkeys (long-tailed macaques) were exposed to a self-control task in two conditions: where the food was hidden under differently colored bowls and where it was visible. When these two conditions were compared, choice shifted from greater preference for the impulsive alternative in the hidden condition to greater preference for the self-control alternative in the visible condition. Additionally, in both conditions, preference shifted from self-control to impulsivity over sessions. These results were explained in terms of the reversed-contingency effect (a propensity to reach for more over less when rewards are visible) and not to a capacity for self-control. In Experiment 2, humans that demonstrated preference for more over less in choice preferred the impulsive alternative when choice to either alternative was followed by the same intertrial interval—a preference that accelerates trial rates relative to preference of the self-control alternative. When trial rates were equated so that neither choice accelerated session’s end, humans demonstrated self-control. These results suggest that Rosati et al.’s demonstration of impulsivity in humans was due to participants’ desire to minimize session time.     

Including Manual Signing as Nontargeted Information When Using a Constant Time Delay Procedure to Teach Receptive Identification of Packaged Food Items

This investigation extends the constant time delay research base by embedding nontargeted information in the task direction when teaching communication skills. Specifically, instructors taught receptive identification of packaged food items to 4 secondary students with moderate to severe disabilities and evaluated generalization to the community. In addition, instructors included the manual sign for each food item. The instructional strategy was a constant time delay procedure using a 5-s delay interval. The intervention, conducted within a multiple probe design across behaviors replicated across students, resulted in the acquisition and generalization of receptive identification of packaged food items by 3 out of 4 of the students. In addition, the students acquired the nontargeted manual signs with an average of 60% percent in the final probe session.     

Metacognitive-like information seeking in lion-tailed macaques: a generalized search response after all?

Previous research has demonstrated that Old World primates (both apes and monkeys) seek information about the location of a hidden food item, unless they are privy to the hiding process. This has been cited as evidence of metacognition. However, these results could also be interpreted using non-metacognitive accounts, including a generalized search response to uncertainty, in which subjects reach for food when it is seen, or search for food until it is spotted. In the present research, lion-tailed macaques were tested on an object-choice task. Conditions varied with respect to the visibility of the baiting process, and whether the location of the hidden food could be inferred by logical exclusion. Additionally, the hidden food could be located visually before a choice was made, by peering under the objects through a Plexiglas tray. Across conditions, monkeys consistently looked for the food when it had not been seen, even if its location could be inferred, despite the fact that these monkeys are capable of inference by exclusion. This suggests that apparently ‘metacognitive’ information seeking in monkeys may instead reflect a generalized search strategy. Alternatively, it is possible that monkeys only have metacognitive access to certain types of knowledge, including that obtained visually. Results are discussed with respect to the likelihood of metacognition in this species and the evolutionary emergence of metacognition across species.     

Incidental retrieval-induced forgetting of location information

Retrieval-induced forgetting (RIF) has been studied with different types of tests and materials. However, RIF has always been tested on the items' central features, and there is no information on whether inhibition also extends to peripheral features of the events in which the items are embedded. In two experiments, we specifically tested the presence of RIF in a task in which recall of peripheral information was required. After a standard retrieval practice task oriented to item identity, participants were cued with colors (Exp. 1) or with the items themselves (Exp. 2) and asked to recall the screen locations where the items had been displayed during the study phase. RIF for locations was observed after retrieval practice, an effect that was not present when participants were asked to read instead of retrieving the items. Our findings provide evidence that peripheral location information associated with an item during study can be also inhibited when the retrieval conditions promote the inhibition of more central, item identity information.     

Processing of repeated letters in search and matching tasks

Several published experiments have used a variant of the matching or “same”-“different” paradigm in which the subject indicates whether or not all of the items in a visual array are the same. Contrary to the results of most paradigms in which subjects process multiple items, reaction time (RT) in this matching task is independent of the number of items in the display (N). One possible explanation of this independence holds that subjects respond to some overall property of the display, such as its general symmetry, and not to the individual items. I tested this hypothesis with a visual search task in which subjects searched a circular display of N=2, 4, or 6 letters for a specified target letter under three stimulus conditions. In the varied condition, the nontarget letters were all different from each other. In the repeated condition, the nontargets were repetitions of the same letter, but a single discrepant letter was always present in the display. The uniform condition also used repeated nontargets, but the negative (target-absent) displays contained N repetitions of a single nontarget item. I found that RT increased at a rate of 27 msec/item for the varied condition, but at only 13 and 8 msec/item in the repeated and uniform conditions, respectively. The slopes in the latter conditions were significantly lower than the slope for the varied condition, and they also differed significantly from each other. Hence, there was some advantage attributable to properties of the overall patterns associated with positive and negative responses, suggesting that at least some responses were based on these properties. There was a much larger advantage, however, attributable to the use of repeated nontargets, regardless of whether the overall patterns differed. This latter observation implies that the flat RT functions observed in matching studies must be interpreted primarily in terms of responses to individual items rather than to the pattern as a whole.     

Effect of two methods of introducing foods during feeding treatment on acceptance of previously rejected items

The effects of using a single food item (e.g. bread) versus using multiple items (e.g. bread, pasta, and rice) when establishing food acceptance via an escape prevention procedure were investigated with six children who presented with food selectivity. Eating was exposed to a differential reinforcement of food acceptance treatment package but food acceptance did not improve. Criterion levels of appropriate eating (> 80% acceptance, < 20% expulsion, and < 20% disruption) were subsequently established with either nonremoval of the spoon or physical guidance for each of the participants. Three of the children were presented with only one food item during acquisition of acceptance. The other children were presented with three different food items from the same food group. It was found that acquisition of acceptance was more rapid for the single‐item group but that food acceptance was more likely to generalize to previously rejected items for the multi‐item group. The implications for clinical intervention are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

The equivalence of target and nontarget processing in visual search

A comparison of a forced-choice visual search task with an item recognition task did not support Neisser’s (1967) hypothesis of a preattentive stage that processes targets and nontargets differentially. In the forced-choice condition, Ss indicated which of two items in a visual display was a target; in item recognition, Ss determined whether or not the single item in the visual display was a target. The size of the memorized set of possible targets was varied from one to six items for both tasks. Latencies increased linearly with memory set size in both conditions; the slopes for forced choice and item recognition were 41.8 and 27.9 msec per item, respectively. The ratio of 1.38 between the two slopes was well fit by Sternberg’s (1967) item recognition model, which predicts a ratio of 1.50.     

Dynamic states in working memory modulate guidance of visual attention: Evidence from an n-back paradigm

Items held in working memory (WM) can automatically bias attention when they reappear in visual displays. Recent evidence, however, suggests that WM biases of attention may be reduced under certain conditions, for example with increasing memory load. We employed a dual task paradigm to investigate how WM biases are affected by dynamic updating of memory contents. 1-back and 2-back versions of a memory task with colour stimuli were interrupted at intervals by an unrelated visual search task. Reappearance in the search display of the item that was currently active in WM guided attention, while suppressed or inactive items did not. We conclude that the rapid updating of memory contents facilitates the shifting of memory representations into different activity states on a moment-to-moment basis. The finding is consistent with models that propose that only one item can be “active” in WM at any one time to guide attention.     

Self-control and tool use in tufted capuchin monkeys (Cebus apella)

Self-control is defined as forgoing immediate gratification to obtain a greater reward. Tool use may relate to self-control because both behaviors may require foresight and deliberate control over one's actions. The authors assessed 20 capuchin monkeys (Cebus apella) for the ability to delay gratification in a tool task. Subjects were given rod-shaped food items that could either be consumed immediately or be carried to an apparatus and used to extract a more preferred food. The authors found that some monkeys were able to exhibit self-control. Monkeys with relatively more tool use experience demonstrated the greatest levels of self-control. These results indicate that capuchins are capable of delaying gratification when a higher quality reinforcer is present and that tool experience can influence levels of self-control in this task.     

Abortion attitudes, 1984-1987-1988: effects of item order and dimensionality.

The comparability of surveys is often hampered by differences in the item order of presentation. The major focus of the present study was to investigate whether a general item or a specific item at the beginning of the questionnaire would affect the endorsement as well as the scalability of a set of attitude items. By using a quasi-A-B-A experimental design for the six abortion items that appeared in the Edmonton Area Survey for the years 1984, 1987, and 1988, we found that the order of presentation of the items affected dramatically the endorsement of the abortion items. Approval of a general item was considerably higher when asked first than when asked after a specific item. In contrast, it was shown by means of a nonparametric item response theory model (the Mokken scale analysis) that the unidimensionality of the six abortion items was not affected by the manipulations of item order (i.e., the six abortion items measured the same concept in the three surveys). It was concluded that the six items are unidimensional and, therefore, create a single scale to measure the change in abortion attitudes across the three periods.     

Disproportionate deficit in associative recognition relative to item recognition in global amnesia

In two experiments, we tested the hypothesis that medial temporal lobe (MTL) amnesic patients and, likewise, diencephalic (DNC) amnesic patients evidence a disproportionate deficit in memory for associations in comparison with memory for single items. In Experiment 1, we equated item recognition in amnesic and control participants and found that, under these conditions, associative recognition remained impaired both for MTL patients and for DNC patients. To rule out an alternative interpretation of the results of Experiment 1, in Experiment 2 we compared the performance of amnesic and control participants on a one-item recognition task and a two-item recognition task that required no memory for the association between members of word pairs. In the MTL group, when single-item recognition was equated to that of the controls, two-item nonassociative pair memory was equivalent as well. In the DNC group, nonassociative pair memory was impaired, but this impairment did not fully account for the impairment in associative memory. These findings indicate that memory for novel associations between items is disproportionately impaired in comparison with memory for single items in amnesia.     

Transfer of self-control in black (Eulemur macaco) and brown (Eulemur fulvus) lemurs: choice of a less preferred food item under a reverse-reward contingency

When presented a choice between two food-type arrays of equivalent size under a reverse-reward contingency, black (Eulemur macaco) and brown (Eulemur fulvus) lemurs transposed their self-control abilities, acquired in a previous experiment, to significantly select the less-desired food item in order to gain access to the more desired one. However, when presented with the choice between two different food-type arrays in which the amount of the less desired food array was larger than the more desired one, large individual differences were revealed: Some subjects established a consistent rule favoring quality or quantity, whereas others exhibited various point of trade-off. These results show that lemurs seem to manage the task considering not only food quantity but also food quality.     

How do African grey parrots (Psittacus erithacus) perform on a delay of gratification task?

Humans and other animals often find it difficult to choose a delayed reward over an immediate one, even when the delay leads to increased pay-offs. Using a visible incremental reward procedure, we tested the ability of three grey parrots to maintain delay of gratification for an increasingly valuable food pay-off. Up to five sunflower seeds were placed within the parrot’s reach, one at a time, at a rate of one seed per second. When the parrot took a seed the trial was ended and the birds consumed the accumulated seeds. Parrots were first tested in daily sessions of ten trials and then with single daily trials. For multiple trial sessions, all three parrots showed some limited improvement across 30 sessions. For single trial sessions, only one parrot showed any increase in seed acquisition across trials. This parrot was also able to consistently obtain two or more seeds per trial (across both multiple and single trial conditions) but was unable to able to wait 5 s to obtain the maximum number of seeds. This parrot was also tested on a slower rate of seed presentation, and this significantly reduced her mean seed acquisition in both multiple and single trial conditions, suggesting that both value of reward available and delay duration impact upon self-control. Further manipulation of both the visibility and proximity of seeds during delay maintenance had little impact upon tolerance of delays for both parrots tested in this condition. This task demanded not just a choice of delayed reward but the maintenance of delayed gratification and was clearly difficult for the parrots to learn; additional training or alternative paradigms are required to better understand the capacity for self-control in this and other species.     

Auditory list memory and interference processes in monkeys.

Memory of 2 rhesus monkeys (Macaca mulatta) was tested in a serial probe recognition task with lists of 4 natural or environmental sounds, different retention intervals, and different manipulations of interference. At short retention intervals, increasing the separation of list items reduced the primacy effect and produced a recency effect. Similar results were shown by increasing interference across lists through item repetitions or making the first 2 list items high-interference items. These results indicated that decreasing first-item performance reduced proactive interference on memory of the last list items. At long (20 s) retention intervals, making the last list items of high interference reduced the recency effect, reduced retroactive interference, and produced a primacy effect. Taken together, interference plays a role in determining the primacy and recency effects of the serial-position function.