Understanding of the relationship between seeing and knowing by tufted capuchin monkeys (Cebus apella)

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. Accepted after revision: 10 September 2001 Electronic Publication     

Do rhesus monkeys (Macaca mulatta) attribute knowledge and ignorance to others?

The ability of 4 rhesus monkeys (Macaca mulatta) to understand the causal connection between seeing and knowing was investigated. The subjects were tested to determine if they could discriminate between information provided by experimenters who randomly alternated between roles of guesser and knower. In a series of tests, the knower either hid food under 1 of 3 cups or watched as someone else hid the food. The guesser waited outside the room or covered her or his head until the food was hidden. The subjects watched this procedure occur but could not see which cup the food was hidden under. The knower pointed to the correct cup while the guesser pointed to an incorrect one. None of the macaques provided any evidence that they realized the different states of knowledge possessed by the guesser and knower. The results are consistent with the hypothesis that rhesus macaques are incapable of making inferences about the mental states of others.     

Inferences about guessing and knowing by chimpanzees (Pan troglodytes)

The visual perspective-taking ability of 4 chimpanzees (Pan troglodytes) was investigated. The subjects chose between information about the location of hidden food provided by 2 experimenters who randomly alternated between two roles (the guesser and the knower). The knower baited 1 of 4 obscured cups so that the subjects could watch the process but could not see which of the cups contained the reward. The guesser waited outside the room until the food was hidden. Finally, the knower pointed to the correct cup while the guesser pointed to an incorrect one. The chimpanzees quickly learned to respond to the knower. They also showed transfer to a novel variation of the task, in which the guesser remained inside the room and covered his head while the knower stood next to him and watched a third experimenter bait the cups. The results are consistent with the hypothesis that chimpanzees are capable of modeling the visual perspectives of others.     

Learning from others’ mistakes in capuchin monkeys (<Emphasis Type="Italic">Cebus apella</Emphasis>)

We investigated whether tufted capuchin monkeys (Cebus apella) learn from others' mistakes. We prepared three kinds of transparent containers having the same appearance: one that could be opened by the lid, one that could be opened from the bottom, and one that could be opened either way. Using each of the first two one-way-open type containers, the monkeys were trained to copy the human demonstrator's action to open the container and obtain a piece of sweet potato contained therein. After this training, the demonstrator showed the monkeys an action that would open or fail to open the third, two-way-open type container. None of the monkeys reliably opened the container by spontaneously compensating for the demonstrator's failure (Experiment 1). In Experiment 2, the same subjects were trained to correct their own mistakes immediately after failure, before we introduced the same test as in Experiment 1. This experience did not result in subjects using the demonstrator's failure to produce a successful action. In Experiment 3, we placed two monkeys face to face. In this situation, the second monkey was presented with the container after the first monkey failed to open it. As a result, two capuchin monkeys capitalized on the partner's failure to correctly guide his/her behavior. Thus, the monkeys monitored not only the outcome of the others' action, but also that action per se. This result suggests that not only humans and apes, but also monkeys may understand the meaning of others' actions in social learning.     

Token-mediated tool-use by a tufted capuchin monkey (Cebus apella)

This research examined token-mediated tool-use in a tufted capuchin monkey (Cebus apella). We conducted five experiments. In experiment 1 we examined the use of plastic color-coded chips to request food, and in experiments 2–5 we examined the use of color-coded chips to request tools. Our subject learned to use chips to request tools following the same general pattern seen in great apes performing analogous tasks, that is, initial discrimination followed by an understanding of the relationship among tokens, tools, and their functions. Our findings are consistent with the view that parallel representational processes underlie the tool-related behavior of capuchins and great apes. Received: 11 March 1998 / Accepted after revision: 19 August 1998     

Cues that chimpanzees do and do not use to find hidden objects

Chimpanzees follow conspecific and human gaze direction reliably in some situations, but very few chimpanzees reliably use gaze direction or other communicative signals to locate hidden food in the object-choice task. Three studies aimed at exploring factors that affect chimpanzee performance in this task are reported. In the first study, vocalizations and other noises facilitated the performance of some chimpanzees (only a minority). In the second study, various behavioral cues were given in which a human experimenter either touched, approached, or actually lifted and looked under the container where the food was hidden. Each of these cues led to enhanced performance for only a very few individuals. In the third study – a replication with some methodological improvements of a previous experiment – chimpanzees were confronted with two experimenters giving conflicting cues about the location of the hidden food, with one of them (the knower) having witnessed the hiding process and the other (the guesser) not. In the crucial test in which a third experimenter did the hiding, no chimpanzee found the food at above chance levels. Overall, in all three studies, by far the best performers were two individuals who had been raised in infancy by humans. It thus seems that while chimpanzees are very good at “behavior reading” of various sorts, including gaze following, they do not understand the communicative intentions (informative intentions) behind the looking and gesturing of others – with the possible exception of enculturated chimpanzees, who still do not understand the differential significance of looking and gesturing done by people who have different knowledge about states of affairs in the world. Received: 8 November 1999 / Accepted after revision: 24 January 2000     

The Origin of Biases in Face Perception

ABSTRACT— Experience with certain types of faces during the first year of development defines which types of faces are more efficiently recognized later in life. In work described here, we found that infants who learned to recognize six monkey faces individually (i.e., each face was individually labeled) over a 3-month period maintained the ability to discriminate monkey faces. However, infants who learned these same six faces categorically (i.e., all faces were labeled "monkey") or were simply exposed to these faces (i.e., faces were not labeled) showed a decline in the ability to discriminate monkey faces. These results suggest that experience individuating faces from 6 to 9 months of age, via labeling, critically shapes the perceptual representation that is responsible for later recognition and discrimination of faces.     

‘Unwilling’ versus ‘unable’: capuchin monkeys’ (Cebus apella) understanding of human intentional action

A sensitivity to the intentions behind human action is a crucial developmental achievement in infants. Is this intention reading ability a unique and relatively recent product of human evolution and culture, or does this capacity instead have roots in our non‐human primate ancestors? Recent work by Call and colleagues (2004) lends credence to the latter hypothesis, providing evidence that chimpanzees are also sensitive to human intentions. Specifically, chimpanzees remained in a testing area longer and exhibited fewer frustration behaviors when an experimenter behaved as if he intended to give food but was unable to do so, than when the experimenter behaved as if he had no intention of giving food. The present research builds on and extends this paradigm, providing some of the first evidence of intention reading in a more distant primate relative, the capuchin monkey (Cebus apella). Like chimpanzees, capuchin monkeys distinguish between different goal‐directed acts, vacating an enclosure sooner when an experimenter acts unwilling to give food than when she acts unable to give food. Additionally, we found that this pattern is specific to animate action, and does not obtain when the same actions are performed by inanimate rods instead of human hands (for a similar logic, see Woodward, 1998 ). Taken together with the previous evidence, the present research suggests that our own intention reading is not a wholly unique aspect of the human species, but rather is shared broadly across the primate order.     

Capuchin monkeys (<Emphasis Type="Italic">Cebus apella</Emphasis>) use conspecifics’ emotional expressions to evaluate emotional valence of objects

Emotional expressions provide important clues to other individuals’ emotional states, as well as the environmental situations leading to such states. Although monkeys often modify their behavior in response to others’ expressions, it is unclear whether this reflects understanding of emotional meanings of expressions, or simpler, non-cognitive processes. The present study investigated whether a New World monkey species, tufted capuchin monkeys, recognize objects as elicitors of others’ expressions. Observer monkeys witnessed another individual (demonstrator) reacting either positively or negatively to the contents of one of two containers and were then allowed to choose one of the containers. The observer preferred the container that evoked positive expressions in the demonstrator and avoided the container that evoked negative expressions. Thus, the monkeys appropriately associated the emotional valence of others’ expressions with the container. This finding supports the view that the ability to represent others’ emotions is not limited to humans and apes.     

Metamemory in tufted capuchin monkeys (Cebus apella)

Whereas evidence for metacognition by nonhuman primates has been obtained in great apes and old world monkeys, it is weaker in new world monkeys. For instance, capuchin monkeys may fail to recognize their own knowledge of the location of invisible bait. In the present study, we tested whether tufted capuchin monkeys would flexibly change their behavior in a delayed matching-to-sample (DMTS) test depending upon the strength of their memory trace of the sample. In Experiment 1, two monkeys were tested on a modified 9-alternative DMTS task with various delays on a computerized display. In some trials, the monkeys could choose whether to go for a memory test or for a simple key touch as an escape from the test. In other trials, they were forced to go for the memory test. Both monkeys escaped from the memory test more often when their matching accuracy on forced tests was lower. In one of the monkeys, the matching accuracies on chosen memory tests decreased more slowly as a function of delay length, and were higher after long delays than those on forced memory tests. This suggests that at least one capuchin monkey was able to recognize the strength of his own memory trace. Experiment 2 employed occasional no-sample tests, in which the monkeys faced the task choice without presentation of any sample for the trial. The monkey who was successful in Experiment 1 declined the memory test more often in no-sample trials than regular trials, further indicating metamemory in this individual. In Experiment 3, this successful monkey received a task, in which he was sometimes able to choose between shape MTS or texture MTS tasks. However, his matching accuracies did not differ between chosen tasks and forced tasks. Thus, the metamemory possessed by this new world monkey species may be more like a flag, showing strength of memory trace, than an elaborate representation showing details of the memory trace.     

Tool-use learning in Tonkean macaques (Macaca tonkeana)

The transmission of tool use is a rare event in monkeys. Such an event arose in a group of semi-free-ranging Tonkean macaques (Macaca tonkeana) in which leaning a pole against the parks fence (branch leaning) appeared and spread to several males. This prompted us to test individual and social learning of this behavior in seven young males. In the first experiment, three males learned individually to obtain a food reward using a wooden pole as a climbing tool. They began using the pole to retrieve the reward only when they could alternatively experience acting on the object and reaching the target. In a second experiment, we first tested whether four other subjects could learn branch leaning after having observed a group-mate performing the task. Despite repeated opportunities to observe the demonstrator, they did not learn to use the pole as a tool. Hence we exposed the latter subjects to individual learning trials and they succeeded in the task. Tool use was not transmitted in the experimental situation, which contrasts with observations in the park. We can conclude that the subjects were not able to recognize the target as such. It is possible that they recognized it and learned the task individually when we alternated the opportunity to act upon the object and to reach the reward. This suggests that these macaques could then have associated the action they exercised upon the pole and the use of the pole as a means to reach the reward.     

Training squirrel monkeys (Saimiri sciureus) to deceive: acquisition and analysis of behavior toward cooperative and competitive trainers

Three squirrel monkeys (Saimiri sciureus) learned to reach toward a container that covered food if a cooperative trainer rewarded such reaches by giving the food. A competitive trainer kept any food found, but wrong selections by this trainer were also rewarded. The monkeys initially reached toward the baited container indiscriminately, but gradually and with the aid of color-cued containers, all 3 reliably reached "honestly" and "deceptively" in the presence of the cooperative and competitive trainers, respectively. The monkeys did not appear to take the trainers' knowledge about the location of the food into account, and deception did not occur if food was placed under the normally unbaited container. With additional containers present, monkeys misled the competitive trainer into selecting the unbaited container farthest from the baited one. Although not indicative of mental attribution, the monkeys' behavior suggests awareness of the acquired communicative function of the reaching response.     

Attention and cue-producing behavior in the monkey

Explicit cue-producing responses were employed to study attending behavior in the monkey. The subjects learned a discrimination based on compound stimuli, a vertical bar embedded on a red ground versus a horizontal bar on a green ground. On some trials only one of the two stimulus components was presented (red versus green or vertical versus horizontal bar), and the animals had the option of responding on the basis of the component presented or transforming it to the compound discriminanda by means of a cue-producing response. Analysis of the choice and cue-producing response behavior showed that (a) both monkeys acquired the discrimination between the compound cues solely on the basis of the color component, (b) mastery of this discrimination did not confer any "habit loading" (discriminative control) on the bar component, and (c) the monkey may prefer to respond on the basis of one component (color) even though it is capable of using both components equally effectively.     

The Search for the Source of Epistemic Good

Knowledge has almost always been treated as good, better than mere true belief, but it is remarkably difficult to explain what it is about knowledge that makes it better. I call this "the value problem." I have previously argued that most forms of reliabilism cannot handle the value problem. In this article I argue that the value problem is more general than a problem for reliabilism, infecting a host of different theories, including some that are internalist. An additional problem is that not all instances of true belief seem to be good on balance, so even if a given instance of knowing p is better than merely truly believing p , not all instances of knowing will be good enough to explain why knowledge has received so much attention in the history of philosophy. The article aims to answer two questions: (1) What makes knowing p better than merely truly believing p ? The answer involves an exploration of the connection between believing and the agency of the knower. Knowing is an act in which the knower gets credit for achieving truth. (2) What makes some instances of knowing good enough to make the investigation of knowledge worthy of so much attention? The answer involves the connection between the good of believing truths of certain kinds and a good life. In the best kinds of knowing, the knower not only gets credit for getting the truth but also gets credit for getting a desirable truth. The kind of value that makes knowledge a fitting object of extensive philosophical inquiry is not independent of moral value and the wider values of a good life.     

The Search for the Source of Epistemic Good

Knowledge has almost always been treated as good, better than mere true belief, but it is remarkably difficult to explain what it is about knowledge that makes it better. I call this "the value problem." I have previously argued that most forms of reliabilism cannot handle the value problem. In this article I argue that the value problem is more general than a problem for reliabilism, infecting a host of different theories, including some that are internalist. An additional problem is that not all instances of true belief seem to be good on balance, so even if a given instance of knowing p is better than merely truly believing p , not all instances of knowing will be good enough to explain why knowledge has received so much attention in the history of philosophy. The article aims to answer two questions: (1) What makes knowing p better than merely truly believing p ? The answer involves an exploration of the connection between believing and the agency of the knower. Knowing is an act in which the knower gets credit for achieving truth. (2) What makes some instances of knowing good enough to make the investigation of knowledge worthy of so much attention? The answer involves the connection between the good of believing truths of certain kinds and a good life. In the best kinds of knowing, the knower not only gets credit for getting the truth but also gets credit for getting a desirable truth. The kind of value that makes knowledge a fitting object of extensive philosophical inquiry is not independent of moral value and the wider values of a good life.     

Discrimination of functionally appropriate and inappropriate throwing tools by captive tufted capuchins (<Emphasis Type="Italic">Cebus apella</Emphasis>)

A tool-throwing task was used to test whether capuchin monkeys understand the difference between functionally appropriate and functionally inappropriate tools. A group of monkeys was trained to obtain a sticky treat from a container outside their enclosure using a projectile attached to one end of an anchored line. Subsequently, these monkeys were given choice tests between functional and nonfunctional versions of tools used in training. A different feature of the tool was varied between alternatives in each choice test. The monkeys chose to use functional tools significantly more often than nonfunctional tools in early exposures to each choice test. A second experiment tested whether these subjects, as well as a second group of minimally trained participants, could distinguish between functional and nonfunctional tools that appeared different from those used in training. A new set of design features was varied between tools in these choice tests. All participants continued to choose functional tools significantly more often than nonfunctional tools, regardless of their tool-throwing experience or the novel appearance of the tools. These results suggest that capuchin monkeys, like chimpanzees studied in similar experiments, are sensitive to a variety of functionally relevant tool features.     

Accountability and judgment processes in a personality prediction task

In this experiment, we investigated the impact of accountability--social pressures to justify one's views to others--on cognitive processing in a personality-prediction task. Subjects were presented with the responses of actual test-takers to 16 items from Jackson's Personality Research Form (PRF) and asked to predict how these individuals responded to an additional set of 16 items from the same test. Subjects were assigned to a no-accountability condition (they learned that all of their responses would be anonymous), a preexposure-accountability condition (they learned of the need to justify their responses before seeing the test-takers' PRF responses), and a postexposure-accountability condition (they learned of the need to justify their responses after seeing the test-takers' PRF responses). Preexposure-accountability subjects reported more integratively complex impressions of test-takers, made more accurate behavioral predictions, and reported more appropriate levels of confidence in their predictions than did either no-accountability or postexposure-accountability subjects. We conclude by considering possible psychological mediators of these effects as well as the broader theoretical implications of the findings for the development of contingency models of judgment and choice.     

Does own experience affect perception of others’ actions in capuchin monkeys (Cebus apella)?

Anticipating another’s actions is an important ability in social animals. Recent research suggests that in human adults and infants one’s own action experience facilitates understanding and anticipation of others’ actions. We investigated the link between first-person experience and perception of another’s action in adult tufted capuchin monkeys (Sapajus apella spp., formerly Cebus apella spp.). In Experiment 1, the monkeys observed a familiar human (actor) trying to open a container using either a familiar or an unfamiliar action. They looked for longer when the actor tried to open the container using a familiar action. In Experiment 2, the actor performed two novel actions on a new container. The monkeys looked equally at the two actions. In Experiment 3, the monkeys were trained to open the container using one of the novel actions in Experiment 2. After training, we repeated the same procedure as in Experiment 2. The monkeys looked for longer when the actor manipulated the container using the action they had practiced than when she used the unfamiliar action. These results show that knowledge derived from one’s own experience impacts perception of another’s action in these New World monkeys.     

Discrimination of moving video images of self by pigeons (<Emphasis Type="Italic">Columba livia</Emphasis>)

The ability to recognize self has been known to be limited to some animal species, but previous research has focused almost exclusively on the animal's reaction to a mirror. Recent studies suggest that the temporal contingency between a subject's action and the corresponding visual scene reflected in a mirror plays an important role in self-recognition. To assess the roles of visual-proprioceptive contiguity in self-recognition, we explored whether pigeons are able to discriminate videos of themselves with various temporal properties. We trained five pigeons to respond to live video images of themselves (live self-movies) and not to video filmed during previous training sessions (pre-recorded self-movies). Pigeons learned to peck trial-unique live self-movies more frequently than pre-recorded self-movies. We conducted two generalization tests after pigeons learned to discriminate between the two conditions. First, discrimination acquired during training sessions was transferred to a test session involving live self-movies and new pre-recorded self-movies. Second, the same pigeons were tested in extinction procedure using delayed live self-movies and new pre-recorded self-movies. Although pigeons responded to delayed presentations of live self-movies more frequently than to new pre-recorded self-movies, the relative response rate to delayed presentation of live self-movies gradually decreased as the temporal discrepancy between pigeons' own behavior and the corresponding video increased. These results indicate that pigeons' discrimination of self-movies with various temporal properties was based on the temporal contiguity between their behavior and its visual feedback. The methodology used in the present experiment is an important step toward improving the experimental analysis of self-recognition in non-human animals.     

I acknowledge your help: capuchin monkeys’ sensitivity to others’ labor

Our society is sustained by wide-ranging cooperation. If individuals are sensitive to others’ gains and losses as well as the amount of labor, they can ensure future beneficial cooperative interaction. However, it is still an open question whether nonhuman primates are sensitive to others’ labor. We asked this question in tufted capuchin monkeys in an experimental food-sharing situation by comparing conditions with labor by two participants equalized (Equal labor condition) or unequalized (Unequal labor condition). The operator monkey pulled the drawer of one of the two food containers placed between two monkeys, each containing a food for him/herself and another for the recipient monkey. The recipient received either high- or low-value food depending on the operator’s choice, whereas the operator obtained the same food regardless of his/her choice. In Unequal labor condition, the operator first had to pull the handle of the board to which the containers were glued and then pull the drawer of one of the containers, while the recipient received food with no labor. In Equal labor condition, the recipient had to pull the handle of the board so that the operator could operate a container. Results showed that operators chose the high-value food container for recipients more often than when the recipient was absent only in Equal labor condition. This suggests that capuchin monkeys are sensitive to others’ labor and actively give food to a partner who has helped them to complete a task.