Sequential responding and planning in capuchin monkeys (Cebus apella)

Under pressure: the interaction between high-stakes contexts and individual differences in decision-making in humans and non-human species

Observed behavior can be the result of complex cognitive processes that are influenced by environmental factors, physiological process, and situational features. Pressure, a feature of a situation in which an individual's outcome is impacted by his or her own ability to perform, has been traditionally treated as a human-specific phenomenon and only recently have pressure-related deficits been considered in relation to other species. However, there are strong similarities in biological and cognitive systems among mammals (and beyond), and high-pressure situations are at least theoretically common in the wild. We hypothesize that other species are sensitive to pressure and that we can learn about the evolutionary trajectory of pressure responses by manipulating pressure experimentally in these other species. Recent literature indicates that, as in humans, pressure influences responses in non-human primates, with either deficits in ability to perform ("choking") or an ability to thrive when the stakes are high. Here, we synthesize the work to date on performance under pressure in humans and how hormones might be related to individual differences in responses. Then, we discuss why we would expect to see similar effects of pressure in non-humans and highlight the existing evidence for how other species respond. We argue that evidence suggests that other species respond to high-pressure contexts in similar ways as humans, and that responses to pressure are a critical missing piece of our understanding of cognition in human and non-human animals. Understanding pressure's effects could provide insight into individual variation in decision-making in comparative cognition and the evolution of human decision-making.

Endogenous cortisol correlates with performance under pressure on a working memory task in capuchin monkeys

Humans often experience striking performance deficits when their outcomes are determined by their own performance, colloquially referred to as “choking under pressure.” Physiological stress responses that have been linked to both choking and thriving are well-conserved in primates, but it is unknown whether other primates experience similar effects of pressure. Understanding whether this occurs and, if so, its physiological correlates, will help clarify the evolution and proximate causes of choking in humans. To address this, we trained capuchin monkeys on a computer game that had clearly denoted high- and low-pressure trials, then tested them on trials with the same signals of high pressure, but no difference in task difficulty. Monkeys significantly varied in whether they performed worse or better on high-pressure testing trials and performance improved as monkeys gained experience with performing under pressure. Baseline levels of cortisol were significantly negatively related to performance on high-pressure trials as compared to low-pressure trials. Taken together, this indicates that less experience with pressure may interact with long-term stress to produce choking behavior in early sessions of a task. Our results suggest that performance deficits (or improvements) under pressure are not solely due to human specific factors but are rooted in evolutionarily conserved biological factors.

Invasive Research on Non-Human Primates-Time to Turn the Page

Simple Summary

Despite increasing ethical concerns, primates are still often used in invasive research (i.e., laboratory research that causes body manipulations causing them pain or distress and not aimed at directly improving their well-being). Here, we will review previous studies showing that primates have complex behaviour and cognition, and that they suffer long-term consequences after being used in invasive research. We will discuss the ethical problems that invasive research on primates posit, the legal protection that they are, to date, granted in different countries, and summarize the past and current attempts to ban this kind of research on primates. We will conclude why, in our opinion, invasive research on primates should be banned, and non-invasive methods should be considered the only possible approach to the study of primates.

Abstract

Invasive research on primates (i.e., laboratory research that implies body manipulations causing pain or distress that is not aimed to directly improve the individuals’ well-being) has a long history. Although some invasive studies have allowed answering research questions that we could not have addressed with other methods (or at least not as quickly), the use of primates in invasive research also raises ethical concerns. In this review, we will discuss (i) recent advances in the study of primates that show evidence of complex behaviour and cognition, (ii) welfare issues that might arise when using primates in invasive research, (iii) the main ethical issues that have been raised about invasive research on primates, (iv) the legal protection that primates are granted in several countries, with a special focus on the principle of the 3Rs, and (v) previous and current attempts to ban the use of primates in invasive research. Based on this analysis, we suggest that the importance of a research question cannot justify the costs of invasive research on primates, and that non-invasive methods should be considered the only possible approach in the study of primates.

Tropical Octopus Abdopus aculeatus Can Learn to Recognize Real and Virtual Symbolic Objects

We used three consecutive operant conditioning tasks to determine whether the tropical octopus Abdopus aculeatus is able to learn to recognize a symbolic object, in either real or virtual forms. In Experiment 1, we examined whether octopuses can be conditioned to a real object (a white ball) and whether such trained individuals can select the conditioned object when they are presented with an unconditioned object. We show that octopuses learned to respond to and select the conditioned white ball in preference to the unconditioned object. In Experiment 2, we examined whether octopuses can be conditioned to an object that gradually changes from real to virtual (i.e., an image of that object on a computer screen). We presented four types of objects, all variations of a white ball, in a stepwise sequence as a conditioned stimulus: a real white ball, a real image of a white ball without a margin, a real image of a white ball centered within a black margin, and a virtual image of a white ball (a video on a computer screen). Individual octopuses learned to respond to all three real objects, and then a subset of these octopuses responded to the virtual object. In Experiment 3, we examined whether an octopus can learn a virtual image of an object with a specific shape not tested in Experiments 1 and 2. We presented octopuses with an image of a white cross, which was placed at various distances (i.e., close, medium, and far). We found that after having learned these images, octopuses could learn the virtual white cross on a computer screen. Furthermore, when we simultaneously presented octopuses with a conditioned virtual object and an unconditioned virtual object, they selected the former. Through these three experiments, we confirmed that A. aculeatus can learn both real and virtual specific objects.

Co-operation of long-term and working memory representations in simultaneous chaining by rhesus monkeys (Macaca mulatta)

We studied the memory representations that control execution of action sequences by training rhesus monkeys (Macaca mulatta) to touch sets of five images in a predetermined arbitrary order (simultaneous chaining). In Experiment 1, we found that this training resulted in mental representations of ordinal position rather than learning associative chains, replicating the work of others. We conducted novel analyses of performance on probe tests consisting of two images "derived" from the full five-image lists (i.e., test B, D from list A→B→C→D→E). We found a "first item effect" such that monkeys responded most quickly to images that occurred early in the list in which they had been learned, indicating that monkeys covertly execute known lists mentally until an image on the screen matches the one stored in memory. Monkeys also made an ordinal comparison of the two images presented at test based on long-term memory of positional information, resulting in a "symbolic distance effect." Experiment 2 indicated that ordinal representations were based on absolute, rather than on relative, positional information because subjects did not link two lists into one large list after linking training, unlike what occurs in transitive inference. We further examined the contents of working memory during list execution in Experiments 3 and 4 and found evidence for a prospective, rather than a retrospective, coding of position in the lists. These results indicate that serial expertise in simultaneous chaining results in robust absolute ordinal coding in long-term memory, with rapidly updating prospective coding of position in working memory during list execution.

Working memory in children assessed with serial chaining and Simon tasks

In the serial chaining task, participants are required to produce a sequence of responses to stimuli in the correct order, and sometimes must determine the sequence at trial outset if stimuli are masked after the first response is made. Similarly, the Simon memory span task presents a participant with a sequence of colors, and the participant must recreate the sequence after the full series is shown. In efforts to directly link the comparative literature on sequential planning behavior and working memory span with the developmental literature, we presented preschool children with the serial chaining task using masked Arabic numerals (N = 44) and the Simon memory span task (N = 65). Older children outperformed younger children in each task, sequencing a longer string of numbers in the serial chaining task and remembering a greater number of items in the Simon task. Controlling for the role of age, there was a significant positive relationship between task scores. These results highlight the emergence of working memory skills that might underlie planning capacities in children using a task developed for nonhuman animals, and the results indicate that improvement in general executive functions could be measured using either or both of these tasks among human children and nonhuman species.

I scan, therefore I decline: The time course of difficulty monitoring in humans (homo sapiens) and macaques (macaca mulatta)

The study of nonhumans' metacognitive judgments about trial difficulty has grown into an important comparative literature. However, the potential for associative-learning confounds in this area has left room for behaviorist interpretations that are strongly asserted and hotly debated. This article considers how researchers may be able to observe animals' strategic cognitive processes more clearly by creating temporally extended problems within which associative cues are not always immediately available. We asked humans and rhesus macaques to commit to completing spatially extended mazes or to decline completing them through a trial-decline response. The mazes could sometimes be completed successfully, but other times had a constriction that blocked completion. A deliberate, systematic scanning process could preevaluate a maze and determine the appropriate response. Latency analyses charted the time course of the evaluative process. Both humans and macaques appeared, from the pattern of their latencies, to scan the mazes through before committing to completing them. Thus monkeys, too, can base trial-decline responses on temporally extended evaluation processes, confirming that those responses have strategic cognitive-processing bases in addition to behavioral-reactive bases. The results also show the value of temporally and spatially extended problems to let researchers study the trajectory of animals' online cognitive processes. (PsycINFO Database Record

Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task

Recent studies of delay of gratification in capuchin monkeys using a rotating tray (RT) task have shown improved self-control performance in these animals in comparison to the accumulation (AC) task. In this study, we investigated whether this improvement resulted from the difference in methods between the rotating tray task and previous tests, or whether it was the result of greater overall experience with delay of gratification tasks. Experiment 1 produced similar performance levels by capuchins monkeys in the RT and AC tasks when identical reward and temporal parameters were used. Experiment 2 demonstrated a similar result using reward amounts that were more similar to previous AC experiments with these monkeys. In Experiment 3, monkeys performed multiple versions of the AC task with varied reward and temporal parameters. Their self-control behavior was found to be dependent on the overall delay to reward consumption, rather than the overall reward amount ultimately consumed. These findings indicate that these capuchin monkeys' self-control capacities were more likely to have improved across studies because of the greater experience they had with delay of gratification tasks. Experiment 4 and Experiment 5 tested new, task-naïve monkeys on both tasks, finding more limited evidence of self-control, and no evidence that one task was more beneficial than the other in promoting self-control. The results of this study suggest that future testing of this kind should focus on temporal parameters and reward magnitude parameters to establish accurate measures of delay of gratification capacity and development in this species and perhaps others.

Comparing species decisions in a dichotomous choice task: adjusting task parameters improves performance in monkeys

In comparative psychology, both similarities and differences among species are studied to better understand the evolution of their behavior. To do so, we first test species in tasks using similar procedures, but if differences are found, it is important to determine their underlying cause(s) (e.g., are they due to ecology, cognitive ability, an artifact of the study, and/or some other factor?). In our previous work, primates performed unexpectedly poorly on an apparently simple two-choice discrimination task based on the natural behavior of cleaner fish, while the fish did quite well. In this task, if the subjects first chose one of the options (ephemeral) they received both food items, but if they chose the other (permanent) option first, the ephemeral option disappeared. Here, we test several proposed explanations for primates' relatively poorer performance. In Study 1, we used a computerized paradigm that differed from the previous test by removing interaction with human experimenters, which may be distracting, and providing a more standardized testing environment. In Study 2, we adapted the computerized paradigm from Study 1 to be more relevant to primate ecology. Monkeys' overall performance in these adapted tasks matched the performance of the fish in the original study, showing that with the appropriate modifications they can solve the task. We discuss these results in light of comparative research, which requires balancing procedural similarity with considerations of how the details of the task or the context may influence how different species perceive and solve tasks differently.

Capuchin monkeys (Cebus apella) modulate their use of an uncertainty response depending on risk

Metacognition refers to thinking about thinking, and there has been a great deal of interest in how this ability manifests across primates. Based on much of the work to date, a tentative division has been drawn with New World monkeys on 1 side and Old World monkeys and apes on the other. Specifically, Old World monkeys, apes, and humans often show patterns reflecting metacognition, but New World monkeys typically do not, or show less convincing behavioral patterns. However, recent data suggest that this difference may relate to other aspects of some experimental tasks. For example, 1 possibility is that risk tolerance affects how capuchin monkeys, a New World primate species, tend to perform. Specifically, it has recently been argued that on tasks in which there are 2 or 3 options, the "risk" of guessing is tolerable for capuchins because there is a high probability of being correct even if they "know they do not know" or feel something akin to uncertainty. The current study investigated this possibility by manipulating the degree of risk (2-choices vs. 6-choices) and found that capuchin monkeys used the uncertainty response more on 6-choice trials than on 2-choice trials. We also found that rate of reward does not appear to underlie these patterns of performance, and propose that the degree of risk is modulating capuchin monkeys' use of the uncertainty response. Thus, the apparent differences between New and Old World monkeys in metacognition may reflect differences in risk tolerance rather than access to metacognitive states.

Looking ahead? Computerized maze task performance by chimpanzees (Pan troglodytes), rhesus monkeys (Macaca mulatta), capuchin monkeys (Cebus apella), and human children (Homo sapiens)

Human and nonhuman primates are not mentally constrained to the present. They can remember the past and-at least to an extent-anticipate the future. Anticipation of the future ranges from long-term prospection such as planning for retirement to more short-term future-oriented cognition such as planning a route through a maze. Here we tested a great ape species (chimpanzees), an Old World monkey species (rhesus macaques), a New World monkey species (capuchin monkeys), and human children on a computerized maze task. All subjects had to move a cursor through a maze to reach a goal at the bottom of the screen. For best performance on the task, subjects had to "plan ahead" to the end of the maze to move the cursor in the correct direction, avoid traps, and reverse directions if necessary. Mazes varied in difficulty. Chimpanzees were better than both monkey species, and monkeys showed a particular deficit when moving away from the goal or changing directions was required. Children showed a similar pattern to monkeys regarding the effects of reversals and moves away from the goal, but their overall performance in terms of correct maze completion was similar to the chimpanzees. The results highlight similarities as well as differences in planning across species and the role that inhibitory control may play in future-oriented cognition in primates.

Exploring Potential Mechanisms Underlying the Lack of Uncertainty Monitoring in Capuchin Monkeys

In a widely used animal-metacognition paradigm, monkeys are positively reinforced with food for correct classifications of stimuli as sparse or dense and punished with timeouts for incorrect responses, but they also have access to an "uncertainty" response that moves them to the next trial without either of these forms of feedback. Rhesus monkeys use this uncertainty response most often for trials on which they are at greatest risk for making an error, suggesting that they are monitoring their ability to make these classifications. Capuchin monkeys do not succeed to the same degree on these tasks-conceivably as a result of differential contingencies in place in all existing studies between the sparse/dense responses (food delivery or timeout) and the uncertainty response (avoidance of a timeout but also no chance for food reward). Here, we used a novel variation of this task in which the outcomes of the three response classes (sparse, dense, uncertain) were functionally equivalent. All responses simply determined the delay interval before presentation of a second task (matching-to-sample), and that task yielded potential food rewards. Overall, capuchin monkeys used the dense and sparse responses appropriately, including some animals that had no prior experience in performing this classification task. However, none used the uncertainty response appropriately even when it was placed on the same contingency plane as the dense and sparse responses. This suggests that the failure of capuchin monkeys to use an uncertainty response is not the result of that response producing a qualitatively different outcome compared to the dense and sparse responses.

What are my chances? Closing the gap in uncertainty monitoring between rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella)

Previous studies have indicated that rhesus monkeys (Macaca mulatta) but not capuchin monkeys (Cebus apella) respond to difficult or ambiguous situations by choosing not to respond or by seeking more information. Here we assessed whether a task with very low chance accuracy could diminish this species difference, presumably indicating that capuchins—compared to macaques—are less risk averse as opposed to less sensitive to signals of uncertainty. Monkeys searched for the largest of 6 stimuli on a computer screen. Trial difficulty was varied, and monkeys could choose to opt out of any trial. All rhesus monkeys, including some with no prior use of the uncertainty response, selectively avoided the most difficult trials. The majority of capuchins sometimes made uncertainty responses, but at lower rates than rhesus monkeys. Nonetheless, the presence of some adaptive uncertainty responding suggests that capuchins also experience uncertainty and can respond to it, though with less proficiency than macaque monkeys.

Prospective memory in children and chimpanzees

Prospective memory (PM) involves remembering to do something at a specific time in the future. Here, we investigate the beginnings of this ability in young children (3-year-olds; Homo sapiens) and chimpanzees (Pan troglodytes) using an analogous task. Subjects were given a choice between two toys (children) or two food items (chimpanzees). The selected item was delivered immediately, whereas the unselected item was hidden in an opaque container. After completing an ongoing quantity discrimination task, subjects could request the hidden item by asking for it (children) or by pointing to the container and identifying the item on a symbol board (chimpanzees). Children and chimpanzees showed evidence of prospective-like memory in this task, as evidenced by successful retrieval of the item at the end of the task, sometimes spontaneously with no prompting from the experimenter. These findings contribute to our understanding of PM from an ontogenetic and comparative perspective.