Performance in a tool-using task by common chimpanzees (Pan troglodytes), bonobos (Pan paniscus), an orangutan (Pongo pygmaeus), and capuchin monkeys (Cebus apella).

Performance by individual animals of three species of great apes (Pan troglodytes, Pan paniscus, and Pongo pygmaeus) and capuchin monkeys (Cebus apella) was assessed by presenting a food treat inside a clear tube. The subjects readily used a straight stick to obtain the food. When sticks were bundled together, the apes immediately unwrapped the bundle to obtain an individual stick, whereas capuchins attempted to insert the bundled sticks. When a misshapen stick was provided, apes, but not capuchins, showed an improvement in terms of modifying the misshapen stick before insertion. Our results indicate that all these species can solve these tasks. However, only the performance of apes is consistent with emerging comprehension of the causal relations required for the avoidance of errors in the more complex tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The performance of bonobos (Pan paniscus), chimpanzees (Pan troglodytes), and orangutans (Pongo pygmaeus) in two versions of an object-choice task.

The object-choice task tests animals’ ability to use human-given cues to find a hidden reward located in 1 of 2 (or more) containers. Great apes are generally unskillful in this task whereas other species including dogs (Canis familiaris) and goats (Capra hircus) can use human-given cues to locate the reward. However, great apes are typically positioned proximal to the containers when receiving the experimenter’s cue whereas other species are invariably positioned distally. The authors investigated how the position of the subject, the human giving the cue and the containers (and the distance among them) affected the performance of 19 captive great apes. Compared to the proximal condition, the distal condition involved larger distances and, critically, it reduced the potential ambiguity of the cues as well as the strong influence that the sight of the containers may have had when subjects received the cue. Subjects were far more successful in the distal compared to the proximal condition. The authors suggest several possibilities to account for this difference and discuss our findings in relation to previous and future object-choice research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Piagetian Liquid Conservation in the Great Apes (Pan paniscus, Pan troglodytes, and Pongo pygmaeus).

An understanding of Piagetian liquid conservation was investigated in 4 bonobos (Pan paniscus), 5 chimpanzees (Pan troglodytes), and 5 orangutans (Pongo pygmaeus). The apes were tested in the ability to track the larger of 2 quantities of juice that had undergone various kinds of transformations. The accuracy of the apes' judgment depended on the shape or number of containers into which the larger quantity was transferred. The apes made their choice mainly on the basis of visual estimation but showed modest success when the quantities were occluded. The results suggest that the apes rely to a greater extent on visual information, although they might have some appreciation of the constancy of liquid quantities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analogical reasoning in a capuchin monkey (Cebus apella).

Previous evidence has suggested that analogical reasoning (recognizing similarities among object relations when the objects themselves are dissimilar) is limited to humans and apes. This study investigated whether capuchin monkeys (Cebus apella) can use analogical reasoning to solve a 3-dimensional search task. The task involved hiding a food item under 1 of 2 or 3 plastic cups of different sizes and then allowing subjects to search for food hidden under the cup of analogous size in their own set of cups. Four monkeys were exposed to a series of relational matching tasks. If subjects reached criterion on these tasks, they were exposed to relational transfer tasks involving novel stimuli. Three of the monkeys failed to reach criterion on the basic relational matching tasks and therefore were not tested further. One monkey, however, revealed above-chance performance on a series of transfer tasks with 3 novel stimuli. This evidence suggests that contrary to previous arguments, a member of a New World monkey species can solve an analogical problem. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What meaning means for same and different: Analogical reasoning in humans (Homo sapiens), chimpanzees (Pan troglodytes), and rhesus monkeys (Macaca mulatta).

Thus far, language- and token-trained apes (e.g., D. Premack, 1976; R. K. R. Thompson, D. L. Oden, & S. T. Boysen, 1997) have provided the best evidence that nonhuman animals can solve, complete, and construct analogies, thus implicating symbolic representation as the mechanism enabling the phenomenon. In this study, the authors examined the role of stimulus meaning in the analogical reasoning abilities of three different primate species. Humans (Homo sapiens), chimpanzees (Pan troglodytes), and rhesus monkeys (Macaca mulatta) completed the same relational matching-to-sample (RMTS) tasks with both meaningful and nonmeaningful stimuli. This discrimination of relations-between-relations serves as the basis for analogical reasoning. Meaningfulness facilitated the acquisition of analogical matching for human participants, whereas individual differences among the chimpanzees suggest that meaning can either enable or hinder their ability to complete analogies. Rhesus monkeys did not succeed in the RMTS task regardless of stimulus meaning, suggesting that their ability to reason analogically, if present at all, may be dependent on a dimension other than the representational value of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tracking the displacement of objects: A series of tasks with great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus) and young children (Homo sapiens).

The authors administered a series of object displacement tasks to 24 great apes and 24 30-month-old children (Homo sapiens). Objects were placed under 1 or 2 of 3 cups by visible or invisible displacements. The series included 6 tasks: delayed response, inhibition test, A not B, rotations, transpositions, and object permanence. Apes and children solved most tasks performing at comparable levels except in the transposition task, in which apes performed better than children. Ape species performed at comparable levels in all tasks except in single transpositions, in which chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) performed better than gorillas (Gorilla gorilla) and orangutans (Pongo pygmeaus). All species found nonadjacent trials and rotations especially difficult. The number of elements that changed locations, the type of displacement, and having to inhibit predominant reaching responses were factors that negatively affected the subjects' performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Great apes' (Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus) understanding of tool functional properties after limited experience.

Primates' understanding of tool functionality has been investigated extensively using a paradigm in which subjects are presented with a tool that they must use to obtain an out-of-reach reward. After being given experience on an initial problem, monkeys can transfer their skill to tools of different shapes while ignoring irrelevant tool changes (e.g., color). In contrast, monkeys without initial training perform poorly on the same tasks. Compared to most monkeys, great apes show a clear propensity for tool using and may not require as much experience to succeed on tool functionality tasks. We investigated this question by presenting 171 apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, and Pongo pygmaeus) with several tool-use problems without giving them initial training or familiarizing them with the test materials. Apes succeeded without experience, but only on problems based on basic properties such as the reward being supported by an object. However, only minimal experience was sufficient to allow them to quickly improve their performance on more complex problems in which the reward was not in contact with the tool. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative assessment of handedness for a coordinated bimanual task in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus).

Hand preferences for a coordinated bimanual task were assessed in a sample of 31 captive gorillas (Gorilla gorilla) and 19 captive orangutans (Pongo pygmaeus) and were compared with chimpanzee (Pan Troglodytes) hand preferences in subjects that were matched on the basis of age, sex, and rearing history. The task required that the apes remove food from the inside edges of a symmetrical polyvinyl chloride pipe presented to them in their home cages. The results indicate significant species differences with chimpanzees showing population-level right-handedness and orangutans showing population-level left-handedness. The gorillas showed a nonsignificant trend toward right-handedness. The results are discussed in terms of possible ecological or biomechanical factors that may influence hand preferences in different ape species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognizing facial cues: Individual discrimination by chimpanzees (Pan troglodytes) and rhesus monkeys (Macaca mulatta).

Faces are one of the most salient classes of stimuli involved in social communication. Three experiments compared face-recognition abilities in chimpanzees (Pan troglodytes) and rhesus monkeys (Macaca mulatta). In the face-matching task, the chimpanzees matched identical photographs of conspecifics' faces on Trial 1, and the rhesus monkeys did the same after 4 generalization trials. In the individual-recognition task, the chimpanzees matched 2 different photographs of the same individual after 2 trials, and the rhesus monkeys generalized in fewer than 6 trials. The feature-masking task showed that the eyes were the most important cue for individual recognition. Thus, chimpanzees and rhesus monkeys are able to use facial cues to discriminate unfamiliar conspecifics. Although the rhesus monkeys required many trials to learn the tasks, this is not evidence that faces are not as important social stimuli for them as for the chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experience and Materials Affect Combinatorial Construction in Tufted Capuchin Monkeys (Cebus apella).

Three movement procedures can combine nesting cups into seriated structures. Reliance on these procedures changes with age in human children, and the putatively most advanced emerges as a predominant procedure at 3 or more years. Six monkeys' (Cebus apella) combinatorial procedures and successes at nesting seriated cups were evaluated. The current study examined whether the procedures used (a) shift toward more efficient procedures after unguided experience, (b) are dependent on the type of object being combined, and (c) can be altered by specific training history. All factors produced a change in procedure for some individuals, suggesting that combinatorial procedure is a product of the dynamic influences of preexisting tendencies to act in certain ways, of environmental circumstances, and of prior experiences. Some monkeys preferred the putatively most cognitively complex procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New evidence on imitation in an enculturated chimpanzee (Pan troglodytes).

Imitation in the great apes continues to be an active field of research and one that is not free of controversy. Several studies suggest that these species do not tend to match the motor movements of the model they observe, but try to achieve the same results using their own methods (emulation of results). In the studies reviewed, gestures have been used very infrequently outside an intraspecific communicative context to evaluate imitation. In fact, the imitation of gestural actions has been tested only in 4 individual great apes. This study assessed a chimpanzee’s (Pan troglodytes) ability to imitate 52 actions in 4 categories. The levels of accuracy attained by the subject in her imitations exceeded those described in previous studies. Moreover, contrary to the idea defended in some articles, the subject seemed to find it easier to imitate gestures than actions with objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation and numerousness judgments of sequentially presented sets of items by chimpanzees (Pan troglodytes).

Summation and numerousness judgments by 2 chimpanzees (Pan troglodytes) were investigated when 2 quantities of M&Ms were presented sequentially, and the quantities were never viewed in their totality. Each M&M was visible only before placement in 1 of 2 cups. In Experiment 1, sets of 1 to 9 M&Ms were presented. In Experiment 2, the quantities in each cup were presented as 2 smaller sets (e.g., ?+?2 vs. 4?+?1). In Experiment 3, the quantities were presented as 3 smaller sets (e.g., 2?+?2?+?3 vs. 3?+?4?+?1). In Experiment 4, an M&M was removed from 1 set before the chimpanzees' selection. In Experiments 1 and 2, the chimpanzees selected the larger quantity on significantly more trials than would be predicted by chance. In Experiments 3 and 4, 1 chimpanzee performed at a level significantly better than chance. Therefore, chimpanzees mentally represent quantity and successfully combine and compare nonvisible, sequentially presented sets of items. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physical intuitions about support relations in monkeys (Macaca fuscata) and apes (Pan troglodytes).

Nonhuman primates, like humans, have demonstrated various physical intuitions. Cacchione and Krist (2004) examined chimpanzees' intuitions about support relations with the violation-of-expectation task. They reported that the chimpanzees possessed intuitions about support, but their intuitions differed from those of humans in part; they were sensitive to “contact/no-contact” and “amount of contact” but not “type of contact” rule. To further explore intuitions about support in nonhuman primates, we conducted similar experiments on monkeys (Japanese monkeys) and apes (chimpanzees). In three experiments, we presented physically possible and impossible events of different support relations to the participants and measured their looking times. The results reveal that the chimpanzees and monkeys detect the violations of “contact/no-contact” and “amount of contact” but not “type of contact” variable. Therefore, the apes and monkeys possess similar intuitions; however, these intuitions differ in part from those of humans. The present study provides new and corroborative evidence of intuitions about support in nonhuman primates. However, this again leads to the question of distinctive understanding about support relations among primate species. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Deterioration of planning ability with age in Japanese monkeys (Macaca fuscata).

To investigate the ability of aged monkeys to plan and the effect of aging on this ability, performance in a food retrieval task was assessed in aged and younger Japanese monkeys (Macaca fuscata). In this task, the monkeys had to retrieve food items by selecting from a set of 9 holes, each of which contained 1 food item. Results showed that task performance declined significantly with age. All monkeys showed, to a greater or lesser extent, some consistent patterns in their sequence of selecting holes for retrieving the food item. An analysis of these selection patterns indicated that the younger monkeys showed more consistent sequences in selection than the aged monkeys. Furthermore, success in the task performance correlated strongly with higher consistency in the sequence of selecting holes. The authors simulated performance for this task by monkeys without any strategies or plans. The results suggest that the empirical data were far more systematic than the simulated data. Thus, the authors conclude that Japanese monkeys have the ability to plan and that this ability to plan deteriorates with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gravity and solidity in four great ape species (Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, Pan paniscus): Vertical and horizontal variations of the table task.

Three experiments modeled after infant studies were run on four great ape species (Gorilla gorilla, Pongo pygmaeus, Pan troglodytes, Pan paniscus) to investigate their reasoning about solidity and gravity constraints. The aims were: (a) to find out if great apes are subject to gravity biased search or display sensitivity for object solidity, (b) to check for species differences, and (c) to assess if a gravity hypothesis or more parsimonious explanations best account for failures observed. Results indicate that great apes, unlike monkeys, show no reliable gravity bias, that ape species slightly differ in terms of their performance, and that the errors made are best explained by a gravity account. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning to cope with two different food distributions: The performance of house mice (Mus musculus domesticus).

Search abilities of mice (Mus musculus domesticus) were evaluated using an arena closed by a ceiling in which 9 food sources (which mice could reach standing on their hind legs) could be arranged according to 2 configurations: a 3?×?3 square matrix and 3 clusters each containing 3 food sources. Testing conditions prevented olfactory and visual cues from being left after visits to food sources, and mice were able to choose alternative routes between food sources. Results showed that mice were more efficient with the matrix than with the cluster configuration. Sex differences were observed: Females improved their performance with both configurations, whereas males improved only with the matrix one. Mice did not develop evident search strategies that would minimize task complexity. Comparison with data published on capuchin monkeys revealed differences, with monkeys performing better with the cluster configuration than with the matrix and applying searching strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing of form stimuli presented unilaterally in humans, chimpanzees (Pan troglodytes), and monkeys (Macaca mulatta).

Visual forms were unilaterally presented using a video-task paradigm to 10 humans, 3 chimpanzees, and 2 rhesus monkeys to determine whether hemispheric advantages existed in the processing of these stimuli. Both accuracy and reaction time served as dependent measures. For the chimpanzees, a significant right hemisphere advantage was found within the first 3 test sessions. The humans and monkeys failed to show a hemispheric advantage as determined by accuracy scores. Analysis of reaction time data revealed a significant left hemisphere advantage for the monkeys. A Visual Half-Field?×?Block interaction was found for the chimpanzees, with a significant left visual field advantage in Block 2, whereas a right visual field advantage was found in Block 4. In the human subjects, a left visual field advantage was found in Block 3 when they used their right hands to respond. The results are discussed in relation to recent reports of hemispheric advantages for nonhuman primates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hysteresis effects in a motor task with cotton-top tamarins (Sanguinus oedipus).

The way human adults grasp an object is influenced by their recent history of motor actions. Previously executed grasps are often more likely to reoccur on subsequent grasps. This type of hysteresis effect has been incorporated into cognitive models of motor planning, suggesting that when planning movements, individuals tend to reuse recently used plans rather than generating new plans from scratch. To the best of our knowledge, the phylogenetic roots of this phenomenon have not been investigated. Here, the authors asked whether 6 cotton-top tamarin monkeys (Saguinus oedipus) would demonstrate a hysteresis effect on a reaching task. The authors tested the monkeys by placing marshmallow pieces within grasping distance of a hole through which the monkeys could reach. On subsequent trials, the marshmallow position changed such that it progressed in an arc in either a clockwise or counterclockwise direction. The authors asked whether the transition point in right- versus left-handed reaches would differ depending on the direction of the progression. The data supported this hysteresis prediction. The outcome provides additional support for the notion that human motor planning strategies may have a lengthy evolutionary history. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation in the chimpanzee (Pan troglodytes).

In this research, we asked whether 2 chimpanzee (Pan troglodytes) subjects could reliably sum across pairs of quantities to select the greater total. Subjects were allowed to choose between two trays of chocolates. Each tray contained two food wells. To select the tray containing the greater number of chocolates, it was necessary to sum the contents of the food wells on each tray. In experiments where food wells contained from zero to four chocolates, the chimpanzees chose the greater value of the summed wells on more than 90% of the trials. In the final experiment, the maximum number of chocolates assigned to a food well was increased to five. Choice of the tray containing the greater sum still remained above 90%. In all experiments, subjects reliably chose the greater sum, even though on many trials a food well on the "incorrect" tray held more chocolates than either single well on the "correct" tray. It was concluded that without any known ability to count, these chimpanzees used some process of summation to combine spatially separated quantities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)