Recognizing Impossible Object Relations: Intuitions About Support in Chimpanzees (Pan troglodytes).

Using looking-time measures, the authors examined untrained chimpanzees' (Pan troglodytes) ability to distinguish between adequate and inadequate support. In 3 experiments, the chimpanzees' sensitivity to different support relations between 2 objects was assessed. In each experiment, the chimpanzees saw a possible and an impossible test event, presented as digital video clips. Looking times in the 3 experiments suggest that chimpanzees use amount of contact between 2 objects, but not type of contact, to distinguish between adequate and inadequate support relations. These results indicate that chimpanzees have some intuition about support phenomena but their sensitivity to relational object properties may differ from that of human infants (Homo sapiens) in this domain. (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)     

Handedness in Chimpanzees (Pan troglodytes) Is Associated With Asymmetries of the Primary Motor Cortex but Not With Homologous Language Areas.

The neurobiology of hand preferences in nonhuman primates is poorly understood. In this study, the authors report the first evidence of an association between hand preference and precentral gyrus-morphology in chimpanzees (Pan troglodytes). Hand preferences did not significantly correlate with other asymmetric brain regions associated with language functions in humans including the planum temporale and frontal operculum. The overall results suggest that homologous regions of the motor cortex control hand preferences in humans and apes and that these functions evolved independently of left-hemisphere specialization for language and speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus monkeys (Macaca mulatta) lack expertise in face processing.

Faces are salient stimuli for primates that rely predominantly on visual cues for recognizing conspecifics and maintaining social relationships. While previous studies have shown similar face discrimination processes in chimpanzees and humans, data from monkeys are unclear. Therefore, three studies examined face processing in rhesus monkeys using the face inversion effect, a fractured face task, and an individual recognition task. Unlike chimpanzees and humans, the monkeys showed a general face inversion effect reflected by significantly better performance on upright compared to inverted faces (conspecifics, human and chimpanzees faces) regardless of the subjects' expertise with those categories. Fracturing faces alters first- and second-order configural manipulations whereas previous studies in chimpanzees showed selective deficits for second-order configural manipulations. Finally, when required to individuate conspecific's faces, i.e., matching two different photographs of the same conspecific, monkeys showed poor discrimination and repeated training. These results support evolutionary differences between rhesus monkeys and Hominoids in the importance of configural cues and their ability to individuate conspecifics' faces, suggesting a lack of face expertise in rhesus monkeys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chimpanzee (Pan troglodytes) consolation: Third-party identity as a window on possible function.

Consolation, that is, postconflict affiliative contact by a bystander toward a recipient of aggression, has acquired an important role in the debate about empathy in great apes because it has been proposed that the reassuring behavior aimed at distressed parties reflects empathetic arousal. However, the function of this behavior is not fully understood. The present study tests specific predictions about the identity of bystanders on the basis of a database of 1102 agonistic interactions and their corresponding postconflict periods in two outdoor-housed groups of captive chimpanzees (Pan troglodytes). We found that recipients of aggression were more likely to be contacted by their own “friends” than by “friends” of the aggressor and that frequent targets of aggression were not more likely to offer consolation than were nontargets of aggression. These findings support the stress reduction hypothesis rather than two proposed alternatives, that is, the opponent relationship repair hypothesis and the self-protection hypothesis. Our results provide further support for relationship quality as a fundamental underlying factor explaining variation in the occurrence of consolation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detection of Grouped and Ungrouped Parts in Visual Patterns by Tufted Capuchin Monkeys (Cebus apella) and Humans (Homo sapiens).

The authors investigated perceptual grouping in capuchin monkeys (Cebus apella) and humans (Homo sapiens). In Experiment 1, 6 monkeys received a visual pattern as the sample and had to identify the comparison stimulus featuring some of its parts. Performance was better for ungrouped parts than for grouped parts. In Experiment 2, the sample featured the parts, and the comparison stimuli, the complex figures: The advantage for ungrouped elements disappeared. In Experiment 3, in which new stimuli were introduced, the results of the previous experiments were replicated. In Experiment 4, 128 humans were presented with the same tasks and stimuli used with monkeys. Their accuracy was higher for grouped parts. Results suggest that human and nonhuman primates use different modes of analyzing multicomponent patterns. (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)     

Comparative and familial analysis of handedness in great apes.

Historically, population-level handedness has been considered a hallmark of human evolution. Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. This paper summarizes published data on handedness in great apes. Comparative analysis indicated that chimpanzees and bonobos show population-level right handedness, whereas gorillas and orangutans do not. All ape species showed evidence of population-level handedness when considering specific tasks. Familial analyses in chimpanzees indicated that offspring and maternal (but not paternal) handedness was significantly positively correlated, but this finding was contingent upon the classification criteria used to evaluate hand preference. Overall, the proportion of right handedness is lower in great apes compared with humans, and various methodological and theoretical explanations for this discrepancy are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhesus monkeys (macaca mulatta) immediately generalize the uncertain response.

Rhesus monkeys (Macaca mulatta) have learned, like humans, to use an uncertain response adaptively under test conditions that create uncertainty, suggesting a metacognitive process by which human and nonhuman primates may monitor their confidence and alter their behavior accordingly. In this study, 4 rhesus monkeys generalized their use of the uncertain response, without additional training, to 2 familiar tasks (2-choice discrimination learning and mirror-image matching to sample) that predictably and demonstrably produce uncertainty. The monkeys were significantly less likely to use the uncertain response on trials in which the answer might be known. These results indicate that monkeys, like humans, know when they do not know and that they can learn to use a symbol as a generalized means for indicating their uncertainty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pointing, withholding information, and deception in capuchin monkeys (Cebus apella).

Brown capuchin monkeys, like 4-year-old children and human-socialized chimpanzees, showed communicative and deceptive pointing in experiments in which they benefited by indicating, accurately or falsely, the location of hidden food. All 3 capuchin monkeys tested (13, 19, and 26 years old) pointed communicatively in the presence of a cooperative trainer. One human-reared monkey pointed without any training and frequently gazed at her human respondent; as with apes, extensive exposure to humans may promote some human-like responses in monkeys. Another capuchin withheld pointing when beneficial, whereas the 3rd learned to obtain the hidden food by pointing deceptively in the presence of a competitive trainer. Such deceptive pointing by one monkey and withholding of information by another suggest that primates' deceptive pointing in an experimental situation is explainable in terms of response inhibition and conditional discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonenculturated Orangutans' (Pongo pygmaeus) Use of Experimenter-Given Manual and Facial Cues in an Object-Choice Task.

Several experiments have been performed, to examine whether nonhuman primates are able to make use of experimenter-given manual and facial (visual) cues to direct their attention to a baited object. Contrary to the performance of prosimians and monkeys, great apes repeatedly have shown task efficiency in experiments such as these. However, many great ape subjects used have been "enculturated" individuals. In the present study, 3 nonenculturated orangutans (Pongo pygmaeus) were tested for their ability to use experimenter-given pointing, gazing, and glancing cues in an object-choice task. All subjects readily made use of the pointing gesture. However, when subjects were left with only gazing or glancing cues, their performance deteriorated markedly, and they were not able to complete the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparative MRI study of the relationship between neuroanatomical asymmetry and interhemispheric connectivity in primates: Implication for the evolution of functional asymmetries.

The authors tested the theory that hemispheric specialization evolved as a consequence of reduced interhemispheric connectivity by examining whether neuroanatomical asymmetries were associated with variation in the ratio of corpus callosum size to brain volume (CC:VOL) and to neocortical surface area (CC:NEO) in human and nonhuman primates. Magnetic resonance images were collected in a sample of 45 primates including 8 New World monkeys, 10 Old World monkeys, 4 lesser apes, 17 great apes, and 6 humans. CC:VOL and CC:NEO were determined and correlated with measures of brain asymmetry. The results indicate that brain asymmetry significantly predicted CC:VOL and CC:NEO. Subsequent analyses revealed that species variation in functional asymmetries in the form of handedness are also inversely related to CC: NEO. Taken together, these results support the hypothesis that leftward brain asymmetries may have evolved as a consequence of reduced interhemispheric connectivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Token transfers among great apes (Gorilla gorilla, Pongo pygmaeus, Pan paniscus, and Pan troglodytes): Species differences, gestural requests, and reciprocal exchange.

Great apes appear to be the nonhuman primates most capable of recognizing trading opportunities and engaging in transfers of commodities with conspecifics. Spontaneous exchange of goods between them has not yet been reported. We tested gorillas (Gorilla gorilla), orangutans (Pongo pygmaeus), bonobos (Pan paniscus), and chimpanzees (Pan troglodytes) in a token-exchange task involving two conspecifics and a human experimenter. Tested in pairs, subjects had to exchange tokens with a partner to obtain food from the experimenter. We observed 4, 5, 264, and 328 transfers of tokens in gorillas, chimpanzees, orangutans, and bonobos, respectively. Most gifts were indirect in gorillas, chimpanzees, and bonobos, whereas most were direct in orangutans. The analysis showed no evidence of calculated reciprocity in interactions. A main finding of the study was the high rate of repeated gifts and begging gestures recorded in orangutans. This raises the question of the meaning of pointing in great apes and their ability to understand the communicative intent of others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparative assessment of psychomotor performance: target prediction by humans and macaques (Macaca mulatta)

Although nonhuman primates such as rhesus monkeys (Macaca mulatta) have been useful models of many aspects of cognition and performance, it has been argued that, unlike humans, they may lack the capacity to respond as predictor-operators. Data from the present series of experiments undermine this claim, suggesting instead a continuity of predictive competency between humans and nonhuman primates. A prediction coefficient was devised to examine the degree to which each subject's response path approximated the optimal predictive strategy. Whereas human subjects (N = 30) generally predicted more accurately, rhesus monkeys (N = 10) also significantly anticipated the movements of the target in all conditions. It appears that humans and rhesus monkeys both exhibit the capacity to respond to where a stimulus is going.     

The relative use of proximity, shape similarity, and orientation as visual perceptual grouping cues in tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

Recent experimental results suggest that human and nonhuman primates differ in how they process visual information to assemble component parts into global shapes. To assess whether some of the observed differences in perceptual grouping could be accounted for by the prevalence of different grouping factors in different species, we carried out 2 experiments designed to evaluate the relative use of proximity, similarity of shape, and orientation as grouping cues in humans (Homo sapiens) and capuchin monkeys (Cebus apella). Both species showed similarly high levels of accuracy using proximity as a cue. Moreover, for both species, grouping by orientation similarity produced a lower level of performance than grouping by proximity. Differences emerged with respect to the use of shape similarity as a cue. In humans, grouping by shape similarity also proved less effective than grouping by proximity but the same was not observed in capuchins. These results suggest that there may be subtle differences between humans and capuchin monkeys in the weighting assigned to different grouping cues that may affect the way in which they combine local features into global shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aping expressions? Chimpanzees produce distinct laugh types when responding to laughter of others.

Humans have the ability to replicate the emotional expressions of others even when they undergo different emotions. Such distinct responses of expressions, especially positive expressions, play a central role in everyday social communication of humans and may give the responding individuals important advantages in cooperation and communication. The present work examined laughter in chimpanzees to test whether nonhuman primates also use their expressions in such distinct ways. The approach was first to examine the form and occurrence of laugh replications (laughter after the laughter of others) and spontaneous laughter of chimpanzees during social play and then to test whether their laugh replications represented laugh-elicited laugh responses (laughter triggered by the laughter of others) by using a quantitative method designed to measure responses in natural social settings. The results of this study indicated that chimpanzees produce laugh-elicited laughter that is distinct in form and occurrence from their spontaneous laughter. These findings provide the first empirical evidence that nonhuman primates have the ability to replicate the expressions of others by producing expressions that differ in their underlying emotions and social implications. The data further showed that the laugh-elicited laugh responses of the subjects were closely linked to play maintenance, suggesting that chimpanzees might gain important cooperative and communicative advantages by responding with laughter to the laughter of their social partners. Notably, some chimpanzee groups of this study responded more with laughter than others, an outcome that provides empirical support of a socialization of expressions in great apes similar to that of humans. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Spider monkeys (Ateles geoffroyi) and capuchin monkeys (Cebus apella) follow gaze around barriers: Evidence for perspective taking?

Gaze following is an adaptive skill that might have been selected in social species, such as many nonhuman primates, to obtain information about food location, predators, and social interactions. The authors investigated the ability of spider monkeys (Ateles geoffroyi) and capuchin monkeys (Cebus apella) to follow the gaze of a human around barriers and the presence of “looking back” behavior. In the 1st experiment, a human looked to a target location inside the testing room, whereas in the 2nd experiment, the human looked behind an opaque barrier placed outside the testing room. The authors compared the frequency of looking at the target location with the corresponding baseline looking frequencies. Both species (a) showed evidence of spontaneous gaze following in the 1st experiment and (b) engaged in gaze following behind the barrier in the 2nd experiment. In contrast, neither species performed “looking back” responses. The authors conclude that both monkey species showed some indication of perspective-taking abilities, although the absence of “looking back” behavior suggests a potential difference from the abilities shown by the great apes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social referencing by young chimpanzees (Pan troglodytes).

Social referencing is the seeking of information from another individual and the use of that information to evaluate a situation. It is a well-documented ability in human infants but has not been studied experimentally in nonhuman primates. Seventeen young nursery-reared chimpanzees (14 to 41 months old) were observed in a standard social referencing paradigm in which they received happy and fear messages concerning novel objects from a familiar human caregiver. Each chimpanzee looked referentially at their caregiver, and the emotional messages that they received differentially influenced their gaze behavior and avoidance of the novel objects. It is concluded that chimpanzees can acquire information about their complex social and physical environments through social referencing and can use emotional information to alter their own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit and explicit category learning by macaques (Macaca mulatta) and humans (Homo sapiens).

An influential theoretical perspective differentiates in humans an explicit, rule-based system of category learning from an implicit system that slowly associates different regions of perceptual space with different response outputs. This perspective was extended for the 1st time to the category learning of nonhuman primates. Humans (Homo sapiens) and macaques (Macaca mulatta) learned categories composed of sine-wave gratings that varied across trials in bar width and bar orientation. The categories had either a single-dimensional, rule-based solution or a two-dimensional, information-integration solution. Humans strongly dimensionalized the stimuli and learned the rule-based task far more quickly. Six macaques showed the same performance advantage in the rule-based task. In humans, rule-based category learning is linked to explicit cognition, consciousness, and declarative reports about the contents of cognition. These results demonstrate an empirical continuity between human and nonhuman primate cognition, suggesting that nonhuman primates may have some structural components of humans’ capacity for explicit cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laterality for visual-spatial processing in two language-trained chimpanzees (Pan troglodytes).

Most reviews of laterality in nonhuman primates indicate that hemispheric asymmetries, similar to those found in humans, are not evident. With the growing evidence for cognitive processes germane to language in apes, in addition to their phylogenetic similarity to humans, they appear to be useful candidates for studies of laterality. Laterality for visual-spatial processing in 2 language-trained chimpanzees was investigated with a visual half-field paradigm. Initially, Ss were taught to manipulate a joystick that controlled the movement of a cursor on a computer monitor to a central fixation point. Ss were then taught a visual discrimination based on the location of a short line contained within a geometric form. Testing consisted of systematic presentation rates of 15, 122, and 226 ms to the left and right visual fields. For half of the trials, Ss used their left hand to respond and used the right hand for the remaining trials. Accuracy and reaction time (RT) were the dependent measures. One S demonstrated significantly faster RTs to stimuli presented to the left visual field (LVF) regardless of which hand was used to respond. The other S demonstrated a significant LVF bias when using the left hand to respond. Results are discussed in the context of current theories on the evolution of laterality and its relation to linguistic functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)