Does Knowledge of the Partner's Need Affect Food Sharing in Tufted Capuchin Monkeys?

Odors are one of the major means of communication for iiouse mice. They influence the behavior and the physiological states of other individuals (Cavaggioni et al., 1999; Vandenbergh, 1994). Examples for influences of odors of a mouse on the physiological states of others have been found from early in 1950s. Odors of female mice kept in groups have been known to lengthen females' estrous cycle (Lee and van der Boot, 1955; 1956) and odors of males were found to induce estrous and to synchronize estrous cycles in females (Whitten, 1956, 1958). Male odors were also found to accelerate puberty in female pups (Vandenbergh, 1969). Odors of strange males were found to block the establishment of pregnancy in females (Bruce, 1959; Parkes and Bruce, 1961), which suggested the role of cognitive processes in some of those influences. The studies especially of the primer effects, as such, tended to be biased towards female mice until these days. Although there have been studies on primer effects in male mice, most of these have concentrated on hormone levels and there have been only a few studies investigating parameters that directly indicate the reproductive activities of males (e.g. sperm density, sperm motility, or sperm velocity). In one of our previous studies, we found that female odors have induced increased sperm density in males (Koyama and Kamimura, 2000). Females were all kept in isolated housing conditions in that study. We chose that housing condition because it had been known that singly housed females come into estrus frequently (Lee and van der Boot, 1955; 1956) and because we thought that odors of estrous females might have stronger influence on the reproductive condition of males compared to odors of diestrous

A temporally stable functional brain network pattern among coordinated brain regions is fundamental to stimulus selectivity and functional specificity during the critical period of brain development. Brain networks that are recruited in time to process internal states of others’ bodies (like hunger and pain) versus internal mental states (like beliefs, desires, and emotions) of others’ minds allow us to ask whether a quantitative characterization of the stability of these networks carries meaning during early development and constrain cognition in a specific way. Previous research provides critical insight into the early development of the theory-of-mind (ToM) network and its segregation from the Pain network throughout normal development using functional connectivity. However, a quantitative characterization of the temporal stability of ToM networks from early childhood to adulthood remains unexplored. In this work, reusing a large sample of children (n = 122, 3–12 years) and adults (n = 33) dataset that is available on the OpenfMRI database under the accession number ds000228, we addressed this question based on their fMRI data during a short and engaging naturalistic movie-watching task. The movie highlights the characters’ bodily sensations (often pain) and mental states (beliefs, desires, emotions), and is a feasible experiment for young children. Our results tracked the change in temporal stability using an unsupervised characterization of ToM and Pain networks DFC patterns using Angular and Mahalanobis distances between dominant dynamic functional connectivity subspaces. Our findings reveal that both ToM and Pain networks exhibit lower temporal stability as early as 3-years and gradually stabilize by 5-years, which continues till adolescence and late adulthood (often sharing similarity with adult DFC stability patterns). Furthermore, we find that the temporal stability of ToM brain networks is associated with the performance of participants in the false belief task to access mentalization at an early age. Interestingly, higher temporal stability is associated with the pass group, and similarly, moderate and low temporal stability are associated with the inconsistent group and the fail group. Our findings open an avenue for applying the temporal stability of large-scale functional brain networks during cortical development to act as a biomarker for multiple developmental disorders concerning impairment and discontinuity in the neural basis of social cognition.

Crockford et al. (2017, Science Advances, 3(11), e1701742) conducted experimental studies in the wild in Africa to investigate the ability of chimpanzees to understand the mental states of other conspecific individuals. Their findings suggest that chimpanzees understand whether or not other individuals are aware of dangers, and they behave differently according to their understanding about the mental states of other individuals.

Previous studies showed that people differ in attributing mental states to themselves and in understanding the mental states of others, but have not explored the differences when people attribute mental states to others at different social distances. The present study adds a 'close other' condition to the Self/Other differentiation paradigm to explore the potential differences in attributing mental states to others with different social distances. It emerged that the time required to reflect on one's self mental state is shortest in mental state attribution, longer when comprehending the mental state of close others, and longest for strangers. This result indicates that Chinese participants distinguish between close others and strangers when performing perspective-taking. When the perspective-shifting of belief-attribution is performed, a beforehand processing of information about close others or strangers does not interfere with the processing of information from oneself subsequently. However, when the information processed in the previous stage cannot be used for subsequent processing, it interferes with the processing of information from close others or strangers in the later stage. The lower the degree of automated processing of pre-processed information, the greater the interference effect produced. This finding indicated that processing the self mental state is automatically activated, but comprehending the mental state of others is not. The comprehension of others' mental states occurs only when required by the task and it entails more cognitive resources to process and maintain.

We examined mirror inspection in tufted capuchin monkeys (Cebus apella). Capuchins were presented with a non-reflective surface for 30 minutes and then a mirror for 3 hours. Inspection of the non-reflective surface did not vary significantly as a function of tool-using ability, age, or sex. Mirror inspection was lowest in older animals, and was greater in animals that used tools than in animals that did not use tools. Mirror-aided self-inspection was not observed. These results indicate that mirror inspection varies with age and tool-using ability in tufted capuchin monkeys. We hypothesize that psychological capacities associated with mirror inspection correspond with those related to the use of tools, and that these capacities facilitate the emergence of self-recognition in some primate species.

Male resource defence during intergroup aggression among tufted capuchin monkeys

The ability of four tufted capuchin monkeys (Cebus apella) to recognize the causal connection between seeing and knowing was investigated. The subjects were trained to follow a suggestion about the location of hidden food provided by a trainer who knew where the food was (the knower) in preference to a trainer who did not (the guesser). The experimenter baited one of three opaque containers behind a cardboard screen so that the subjects could not see which of the containers hid the reward. In experiment 1, the knower appeared first in front of the apparatus and looked into each container; next, the guesser appeared but did not look into any containers. Then the knower touched the correct cup while the guesser touched one of the three randomly. The capuchin monkeys gradually learned to reach toward the cup that the knower suggested. In experiment 2, the subjects adapted to a novel variant of the task, in which the guesser touched but did not look into any of the containers. In experiment 3, the monkeys adapted again when the knower and the guesser appeared in a random order. These results suggest that capuchin monkeys can learn to recognize the relationship between seeing and knowing.

The abstract concept of equivalence is considered one of the bases of higher-order cognition, and it has been the subject of considerable research in comparative cognition. This study examined the conditions under which tufted capuchin monkeys (Cebus apella) are able to acquire an identity concept. Six capuchin monkeys were trained to solve a visual matching-to-sample (MTS) task on the basis of perceptual identity. The acquisition of the identity rule was inferred from the subject's ability to solve transfer tests with novel stimuli. We evaluated the ability of the capuchin monkeys to match the shape of novel stimuli after training with both several small stimulus sets (Experiment 1) and a large stimulus set (Experiment 2). Moreover, we examined the ability of capuchins to transfer the concept to novel visual dimensions, such as colour and size and to transfer to novel spatial arrangements of the stimuli (Experiment 2). We demonstrated that the ability of capuchins to match novel stimuli was improved by increasing the number of stimuli used during training (Experiments 1 and 2) and that after a widely applicable identity concept based on the stimulus shape was acquired, the capuchins were able to match stimuli according to an identity rule based on both the colour and size of the stimuli and when the spatial arrangement of the stimuli was varied (Experiment 2). This study is the first to demonstrate that the size of the training set affects the acquisition of an abstract identity concept in an MTS task in non-human primates.

Four tufted capuchin monkeys (Cebus apella) were trained to choose from 2 hook-like tools, 1 of which successfully led to collecting food, whereas the other did not because of inappropriate spatial arrangement of the tool and the food. In Experiment 1, all of the monkeys successfully learned the basic task. The monkeys performed successfully with tools of novel colors and shapes in Experiments 2-5. These results demonstrate that the monkeys used the spatial arrangement of the tool and the food as a cue. However, they failed when there were obstacles (Experiment 6) or traps (Experiment 7) on the path along which the monkeys dragged tools. These results may suggest that capuchin monkeys understand the spatial relationship between 2 items, namely, food and the tool, but do not understand the spatial relationship among 3 items, namely, food, tool, and the environmental condition. The possible role of stimulus generalization is also considered.

The authors provided different forms of environmental enrichment to six old laboratory male tufted capuchin monkeys (Cebus apella) and studied the behavior of the monkeys during a baseline period and during three enrichment periods. Each observation period lasted 5 d, with an interval of 6 d between periods. During the first enrichment period, the authors provided Buster cubes and wood cylinders with drilled holes filled with gum arabic. During the second enrichment period, monkeys were provided with a deep litter of bark shavings, and during the third enrichment period, they were given Buster cubes, wood cylinders and bark shavings. When provided with enrichment, the monkeys engaged in natural, species-specific activities and began to exhibit behavioral profiles that more closely resembled those of their natural counterparts. This suggests that their psychological well-being had improved and that group housing combined with environmental enrichment can improve the welfare of old laboratory tufted capuchin monkeys that were previously housed individually.

Tufted capuchin monkeys (Cebus apella), a species of New World primates, are known to be adept at various complex tool use both in the laboratory and in the wild. With their manual dexterity, they work as a helper for quadriplegic people. Social intelligence hypothesis, which places social intelligence as a major factor to advance complex information processing capability, predicts advanced social intelligence in this species with highly developed physical intelligence. In this paper, I describe a series of studies on social intelligence of this species in our comparative cognition laboratory at Kyoto University. As a competitive aspect of social intelligence, we analyzed spontaneous deceptive behavior between the monkeys. Two monkeys, dominant and subordinate, faced each other in the transparent boxes and two food cups were placed between them. When the subordinate monkey opened the baited cup, the dominant opponent was able to usurp the food. Some of the subordinates started to open the empty cup first: a behavior that could be interpreted as a deceptive act. As a cooperative aspect, we showed that two monkeys cooperated by dividing a sequence of behavior necessary to obtain rewards. This behavior continued even when only one of the participants received a reward if their roles were switched every trial; a reciprocal altruism was shown. To examine whether such complicated social behaviors reflect processes of mentalizing, we asked whether capuchin monkeys have cognitive components underlying them. We found that the monkeys are capable of recognizing attentional states of humans, inferring consequences of other's behavior, recognizing other's knowledge status, inferring the cause of other's emotional expression, and recognizing other's welfare. Thus these primitive aspects of mentalizing are clearly shared in species that is much more distant from humans than apes.

Testing the two sides of indirect reciprocity in tufted capuchin monkeys

This study examined hand preference for tool use and spontaneous non‐tool actions in tufted capuchin monkeys (Cebus apella). We noted a lack of lateral bias across measures, and greater strength of hand preference for tool use than for self‐directed or feeding activities. Animals that used tools exhibited a population‐level right‐hand bias for self‐touching whereas animals that did not use tools exhibited a lack of lateral bias for this measure. Our findings are consistent with views that hand preference is expressed more strongly for tool use than for non‐tool activities, and that lateral bias for self‐directed behavior is related to problem‐solving skills in primates.

The purpose of this research was to examine aimed throwing of stones by tufted capuchin monkeys (Cebus apella). Three capuchins (two adults and one juvenile) threw stones at a stationary target located outside their home cages. The monkeys subsequently discriminated between stationary targets and threw stones at a moving target. Each subject exhibited a distinct manual and postural throwing preference. These results demonstrate that capuchins have throwing capabilities which are thought to have been associated with early hominid evolution.

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism.