Gibbons exploit information about what a competitor can see

Animal Cognition - How much nonhuman animals understand about seeing has been the focus of comparative cognition research for decades. Many social primates (and other species) are sensitive to cues...     

Chimpanzees know what others know, but not what they believe

There is currently much controversy about which, if any, mental states chimpanzees and other nonhuman primates understand. In the current two studies we tested both chimpanzees’ and human children’s understanding of both knowledge-ignorance and false belief - in the same experimental paradigm involving competition with a conspecific. We found that whereas 6-year-old children understood both of these mental states, chimpanzees understood knowledge-ignorance but not false belief. After ruling out various alternative explanations of these and related findings, we conclude that in at least some situations chimpanzees know what others know. Possible explanations for their failure in the highly similar false belief task are discussed.     

Implicit sequence learning in ring‐tailed lemurs (Lemur catta)

Implicit learning involves picking up information from the environment without explicit instruction or conscious awareness of the learning process. In nonhuman animals, conscious awareness is impossible to assess, so we define implicit learning as occurring when animals acquire information beyond what is required for successful task performance. While implicit learning has been documented in some nonhuman species, it has not been explored in prosimian primates. Here we ask whether ring‐tailed lemurs (Lemur catta) learn sequential information implicitly. We tested lemurs in a modified version of the serial reaction time task on a touch screen computer. Lemurs were required to respond to any picture within a 2 × 2 grid of pictures immediately after its surrounding border flickered. Over 20 training sessions, both the locations and the identities of the images remained constant and response times gradually decreased. Subsequently, the locations and/or the identities of the images were disrupted. Response times indicated that the lemurs had learned the physical location sequence required in original training but did not learn the identity of the images. Our results reveal that ring‐tailed lemurs can implicitly learn spatial sequences, and raise questions about which scenarios and evolutionary pressures give rise to perceptual versus motor‐implicit sequence learning.     

A comparative analysis of serial ordering in ring-tailed lemurs (Lemur catta)

Research over the last 25 years has demonstrated that animals are able to organize sequences in memory and retrieve ordered sequences without language. Qualitative differences have been found between the serial organization of behavior in pigeons and monkeys. Here the authors test serial ordering abilities in ring-tailed lemurs, a strepsirrhine primate whose ancestral lineage diverged from that of monkeys, apes, and humans approximately 63 million years ago. Lemurs' accuracy and response times were similar to monkeys, thus suggesting that they may share mechanisms for serial organization that dates to a common primate ancestor.     

Chimpanzees do not take into account what others can hear in a competitive situation

Chimpanzees (Pan troglodytes) know what others can and cannot see in a competitive situation. Does this reflect a general understanding the perceptions of others? In a study by Hare et al. (2000) pairs of chimpanzees competed over two pieces of food. Subordinate individuals preferred to approach food that was behind a barrier that the dominant could not see, suggesting that chimpanzees can take the visual perspective of others. We extended this paradigm to the auditory modality to investigate whether chimpanzees are sensitive to whether a competitor can hear food rewards being hidden. Results suggested that the chimpanzees did not take what the competitor had heard into account, despite being able to locate the hiding place themselves by the noise.     

Dealing with conflicting information: young children's reliance on what they see versus what they are told

Children often learn about the world through direct observation. However, much of children's knowledge is acquired through the testimony of others. This research investigates how preschoolers weigh these two sources of information when they are in conflict. Children watched as an adult hid a toy in one location. Then the adult told children that the toy was in a different location (i.e. false testimony). When retrieving the toy, 4- and 5-year-olds relied on what they had seen and disregarded the adult's false testimony. However, most 3-year-olds deferred to the false testimony, despite what they had directly observed. Importantly, with a positive searching experience based on what they saw, or with a single prior experience with an adult as unreliable, 3-year-olds subsequently relied on their first-hand observation and disregarded the adult's false testimony. Thus, young children may initially be credulous toward others' false testimony that contradicts their direct observation, but skepticism can develop quickly through experience.     

Multiple measures of hand-use lateralization in the ring-tailed lemur (Lemur catta)

Evaluated a free-ranging matriline of 13 ring-tailed lemurs (Lemur catta) from videotaped records for lateralized hand use with 2 tasks and 4 measures: food reaching, feeding posture, duration of food holding, and manipulation of food between mouth and hand while eating. Binomial z scores determined 7 lemurs to be left preferent in reaching, 3 right, and 3 ambipreferent. Ideographic analyses suggested possible sex-linked and early experience twin effects. When compared to right and ambipreferent lemurs, left reach preferent lemurs used the left hand more but bimanuals grasped less in food holding and also engaged in less hand-mouth food manipulation. The tendency to manipulate food was not correlated with bimanual holding but was inversely related to left hand holding and directly related to right hand holding. These patterns are discussed as possible precursors of human bimanual manipulation.     

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.     

What you want (and do not want) affects what you see (and do not see): avoidance social goals and social events

Two studies examined the influence of approach and avoidance social goals on memory for and evaluation of ambiguous social information. Study 1 found that individual differences in avoidance social goals were associated with greater memory of negative information, negatively biased interpretation of ambiguous social cues, and a more pessimistic evaluation of social actors. Study 2 experimentally manipulated social goals and found that individuals high in avoidance social motivation remembered more negative information and expressed more dislike for a stranger in the avoidance condition than in the approach condition. Results suggest that avoidance social goals are associated with emphasizing potential threats when making sense of the social environment.     

Expectations about numerical events in four lemur species (Eulemur fulvus, Eulemur mongoz, Lemur catta and Varecia rubra)

Although much is known about how some primates—in particular, monkeys and apes—represent and enumerate different numbers of objects, very little is known about the numerical abilities of prosimian primates. Here, we explore how four lemur species (Eulemur fulvus, E. mongoz, Lemur catta, and Varecia rubra) represent small numbers of objects. Specifically, we presented lemurs with three expectancy violation looking time experiments aimed at exploring their expectations about a simple 1+1 addition event. In these experiments, we presented subjects with displays in which two lemons were sequentially added behind an occluder and then measured subjects duration of looking to expected and unexpected outcomes. In experiment 1, subjects looked reliably longer at an unexpected outcome of only one object than at an expected outcome of two objects. Similarly, subjects in experiment 2 looked reliably longer at an unexpected outcome of three objects than at an expected outcome of two objects. In experiment 3, subjects looked reliably longer at an unexpected outcome of one object twice the size of the original than at an expected outcome of two objects of the original size. These results suggest that some prosimian primates understand the outcome of simple arithmetic operations. These results are discussed in light of similar findings in human infants and other adult primates.This revised version was published online in March 2005 with corrections to Fig. 6.     

Children (but not adults) can inhibit false memories

The role of inhibition in children's (5-, 7-, and 11-year-olds') false memory illusions in the Deese-Roediger-McDermott (DRM) paradigm was examined using a list-wise directed-forgetting procedure. Children studied either a single DRM list (control) or two DRM lists in succession with a directed-remembering instruction or a directed-forgetting instruction between list presentations. The findings indicated that, like adults, children effectively suppressed the output of true memories when given a directed-forgetting instruction. Unlike adults, whose false memories are not attenuated in directed-forgetting conditions, children suppressed false memories at recall in the directed-forgetting condition. Because recognition data indicated that the children did generate false memories regardless of instruction, it appears that although adults' false memories are generated automatically and do not become part of their conscious experience, children's false memories are produced with greater effort and conscious processing, and as a result are easier to suppress at output.     

Decision-makers use social information to update their preferences but choose for others as they do for themselves

People's risky decisions are susceptible to the social context in which they take place. Across three experiments using different paradigms, we investigated the influence of three social factors upon participants' decisions: the recipient of the decision-making outcome (self, other, or joint), the nature of the relationship with the other agent (friend, stranger, or teammate), and the type of information that participants received about others' preferences: none at all, general information about how previous participants had decided, or information about a specific partner's preference. We found that participants' decisions about risk did not differ according to whether the outcome at stake was their own, another agent's, or a joint outcome, nor according to the type of information available. Participants did, however, adjust their preferences for risky options in light of social information.     

Analyses of feeding lateralization in the small-eared bushbaby (Otolemur garnettii): a comparison with the ring-tailed lemur (Lemur catta)

Feeding related lateralization was examined in a population of 23 small-eared bushbabies (Otolemur garnettii). The three measures used to determine lateralization were food reaching, holding, and manipulation. Sex and age differences were found, with adult females showing a strong right bias and adult males a left bias. Juvenile males were weakly lateralized and less consistent across measures than adult animals. The use of standard scores to assess lateralization allowed species comparisons to be made. The results of this study were compared with results from a previous study on lateralization in the ring-tailed lemur (Lemur catta). Species comparisons found sex differences to be a stronger factor in lateralization than species differences.     

Joint attention: inferring what others perceive (and don't perceive)

Research has shown that observers automatically align their attention with another's gaze direction. The present study investigates whether inferring another's attended location affects the observer's attention in the same way as observing their gaze direction. In two experiments, we used a laterally oriented virtual human head to prime one of two laterally presented targets. Experiment 1 showed that, in contrast to the agent with closed eyes, observing the agent with open eyes facilitated the observer's alignment of attention with the primed target location. Experiment 2, where either sunglasses or occluders concealed the agent's eye direction, showed that only the agent with the sunglasses facilitated the observer's alignment of attention with the target location. Taken together, the data demonstrate that head orientation alone is not sufficient to trigger a shift in the observer's attention, that gaze direction is crucial to this process, and that inferring the region to which another person is attending does facilitate the alignment of attention.     

Bee-eaters (<Emphasis Type="Italic">Merops orientalis</Emphasis>) respond to what a predator can see

Two sets of experiments are reported that show that the small green bee-eater (Merops orientalis, a small tropical bird) can appreciate what a predator can or cannot see. Bee-eaters avoid entering the nest in the presence of a potential nest predator. In the first set of experiments bee-eaters entered the nest more frequently when the predator was unable to see the nest from its position, as compared to an approximately equidistant position from which the nest could be seen. In the second set of experiments bee-eaters entered the nest more frequently when the predator was looking away from the nest. The angle of gaze from the nest was associated significantly positively with the probability of entering the nest whereas the angle from the bird was not. Birds showed considerable flexibility as well as individual variation in the possible methods of judging the predator's position and direction of gaze. Electronic Publication     

Chimpanzees (Pan troglodytes) conceal visual and auditory information from others

Chimpanzees (Pan troglodytes) competed with a human for food. The human sat inside a booth, with 1 piece of food to her left and 1 to her right, which she could retract from her chimpanzee competitor's reach as needed. In Experiment 1, chimpanzees could approach either side of the booth unseen but then had to reach through 1 of 2 tunnels (1 clear, 1 opaque) for the food. In Experiment 2, both tunnels were clear and the human was looking away, but 1 of the tunnels made a loud noise when it was opened. Chimpanzees preferentially reached through the opaque tunnel in the first study and the silent tunnel in the second, successfully concealing their taking of the food from the human competitor in both cases. These results suggest that chimpanzees can, in some circumstances, actively manipulate the visual and auditory perception of others by concealing information from them.     

Altruistic punishment: what field data can (and cannot) demonstrate

The rarity of altruistic punishment in small-scale societies should not be interpreted as evidence that altruistic punishment is not an important determinant of cooperation in general. While it is essential to collect field data on altruistic punishment, this kind of data has limitations. Laboratory experiments can help shed light on the role of altruistic punishment "in the wild."     

Chimpanzees (Pan troglodytes) know what can be seen from where

Visual perspective taking research has established that chimpanzees recognize what others can or cannot see in the presence of occluding barriers. Less is known about chimpanzees’ appreciation of what they themselves can or cannot see in similar situations. Additionally, it is unclear whether chimpanzees must rely on others’ gaze cues to solve such tasks or whether they have a more general appreciation of what can be seen from where. Hence, we investigated chimpanzees’ ability to anticipate what they would or would not be able to see from different visual perspectives. Food was hidden among arrays of open containers, with different containers providing visual access from unique viewing perspectives. Chimpanzees immediately adopted the correct perspective for each container type. Follow-up experiments showed that they were not simply moving to align themselves with visible openings. Our study thus suggests that chimpanzees have good visual perspective taking abilities with regard to themselves as well as others, and that both likely reflect a more general knowledge, at least implicit, of what can be seen from where.

Eye gaze cannot be ignored (but neither can arrows)

Recent studies have shown that switch costs (i.e., slower responding on task-alternation trials than on task-repetition trials) are not observed when on the preceding trial a no-go signal instructed the participant to withhold the response to the target stimulus. This finding suggests that neither task set is inhibited on no-go trials, and that the origin of switch costs is located in the application of the task set to the target stimulus. However, these studies also showed that responding after a no-go trial is substantially slower than after a go trial. This suggests that both task sets are inhibited on no-go trials and that switch costs originate from the preparation of a task set. In two experiments we created conditions that revealed an absence of switch costs in conjunction with relatively fast responding after no-go trials. Together these findings confirm that switch costs originate from the application of the task set.