Hand preferences for a coordinated bimanual task in 110 chimpanzees (Pan troglodytes): Cross-sectional analysis.

Hand preference for a coordinated bimanual task was assessed in a sample of 110 chimpanzees (Pan troglodytes). Subjects were presented with opaque tubes, the inside of which was coated with peanut butter. The hand and finger used to extract the peanut butter was recorded in 2 test sessions. A population right-hand bias was found. Juvenile and adolescent subjects were less lateralized than adults. All subjects primarily used their index finger to extract peanut butter. Use of the index finger was higher in adults and adolescents compared with juveniles. The results suggest that coordinated bimanual tasks (a) elicit strong hand preferences at the individual level and (b) elicit population level right-handedness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand use and gestural communication in chimpanzees (Pan troglodytes).

Hand use in gestural communication was examined in 115 captive chimpanzees (Pan troglodytes). Hand use was measured in subjects while they gestured to food placed out of their reach. The distribution of hand use was examined in relation to sex, age, rearing history, gesture type, and whether the subjects vocalized while gesturing. Overall, significantly more chimpanzees, especially females and adults, gestured with their right than with their left hand. Foods begs were more lateralized to the right hand than pointing, and a greater prevalence of right-hand gesturing was found in subjects who simultaneously vocalized than those who did not. Taken together, these data suggest that referential, intentional communicative behaviors, in the form of gestures, are lateralized to the left hemisphere in chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early sensorimotor development in chimpanzees (Pan troglodytes).

Examined the cognitive and locomotor development of 4 chimpanzees (Pan troglodytes) during their 1st yr of life with Piagetian theory and method as paradigm. The infant chimpanzees progressed through the same 4 stages of development as babies do. However, the chimpanzees seemed less developed than babies in object exploration and in object–object combination. When chimpanzee early cognition is compared with that of other nonhuman primates, chimpanzees appear more advanced than gorillas, capuchins, and macaques in these same areas of cognition and similar to orangutans. A unitary explanation of the relative advances and delays in chimpanzee early cognition, which refers to the relation between rates of locomotor and cognitive development, is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posture and reaching in chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus).

Hand preference in reaching was assessed under 2 postural adjustment conditions in 40 chimpanzees (Pan troglodytes) and 6 orangutans (Pongo pygmaeus). The postural conditions were quadrupedal and upright, during which reaching for food was scored on a minimum of 50 trials. Results indicated no population preference during quadrupedal reaching, but a right-hand population preference was found during upright reaching. There were no significant effects of age or sex on either the direction or strength of hand preference. Early rearing history affected the strength of hand preference but not direction. The results suggest that posture is an important factor in the assessment of hand preference in great apes and may have important evolutionary consequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Color preferences in gorillas (Gorilla gorilla gorilla) and chimpanzees (Pan troglodytes).

Color plays an important biological role in the lives of many animals, with some species exhibiting preferences for certain colors over others. This study explored the color preferences of two species of ape, which, like humans, possess trichromatic color vision. Six western lowland gorillas, and six chimpanzees, housed in Belfast Zoological Gardens, were exposed to three stimuli (cloths, boxes, sheets of acetate) in red, blue, and green. Six stimuli of the same nature, in each of the three colors, were provided to both species for 5 days per stimulus. The amount of interest that the animals showed toward each stimulus of each color was recorded for 1 hr. Results showed that the apes, both when analyzed as two separate groups, and when assessed collectively, showed significant color preferences, paying significantly less attention to the red-, than to the blue- or green-colored stimuli. The animals' interest in the blue- and green-colored stimuli did not differ significantly. Overall, the findings suggest that gorillas and chimpanzees, our closest living relatives, may harbor color preferences comparable to those of humans and other species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A vocabulary test for chimpanzees (Pan troglodytes).

Presented a vocabulary test to 4 cross-fostered chimpanzees (4–6 years old) who had learned some American Sign Language (ASL) in the laboratory. 35 mm color slides were projected on a screen that could be seen by the chimpanzee Ss but not by the human observers. There were 2 observers: 01 was the questioner in the testing room with the Ss; 02 was in a different room. Neither observer could see the other, or the responses of the other observer. 01 and 02 agreed in their readings of both correct and incorrect signs, and most of the signs were the correct ASL names of the slides. To show that the chimpanzees were naming natural language categories—that the sign DOG could refer to any dog, FLOWER to any flower, SHOE to any shoe—each test trial was a 1st trial, in that test slides were presented only once. Analysis of errors showed that 2 aspects of the signs, gestural form and conceptual category, governed the distribution of errors. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manual laterality in chimpanzees (Pan troglodytes) in complex tasks.

To determine the manual laterality of a sample of 24 chimpanzees, 4 problem apparatuses were used, the solution for which (obtaining a food item) required the use of 1 or both hands in sequential, simultaneous, or both sequential and simultaneous actions. The majority of the subjects showed significant and consistent hand preferences, especially in the actions that required a precision grip. The results obtained suggest the existence of factors linked to the specific characteristics of the task to be performed and to the ontogenetic maturation of the subject, which would influence the directionality and degree of the hand preference displayed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scale-model comprehension by chimpanzees (Pan troglodytes).

The ability of chimpanzees (Pan troglodytes) to recognize the correspondence between a scale model and its real-world referent was examined. In Experiments 1 and 2, an adult female and a young adult male watched as an experimenter hid a miniature model food in 1 of 4 sites in a scale model. Then, the chimpanzees were given the opportunity to find the real food item that had been hidden in the analogous location in the real room. The female performed significantly above chance, whereas the male performed at chance level. Experiments 3 and 4 tested 5 adult and 2 adolescent chimpanzees in a similar paradigm, using a scale model of the chimpanzees' outdoor area. Results indicate that some adult chimpanzees were able to reliably demonstrate an understanding of the relationship between a scale model and the larger space it represented, whereas other subjects were constrained by inefficient and unsuccessful search patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of self-recognition in chimpanzees (Pan troglodytes).

Chimpanzees demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. 12 young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 yrs old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2.5-yr-olds exhibited clear evidence of self-recognition. All chimpanzees exhibited both self-directed behaviors and contingent movements. These results suggest that self-recognition occurs at a slightly older age in chimpanzees than in human infants. In humans, self-recognition is linked with other cognitive abilities. The results conform to the general pattern that great apes exhibit many cognitive skills comparable to those of 2-yr-old humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral bias in infant chimpanzees (Pan troglodytes).

This study documents the presence, strength, and direction of lateralization in chimpanzees (Pan troglodytes) over the first 3 months of life. Nursery-reared chimpanzees (7 males and 5 females) were repeatedly assessed on a behavioral scale. Lateral bias was measured for 4 behaviors: hand-to-mouth, hand-to-hand, defensive grasp, and first step. Hand-to-mouth was significantly lateralized for the sample. Eight of the 10 chimpanzees that showed hand-to-mouth used the right hand. Lateral bias for defensive grasp was positively related to lateral bias both of first step and of hand-to-mouth. Lateral bias in hand-to-mouth was inversely related to lateral bias in hand-to-hand. Strength of lateralization increased as chimpanzees matured. These laterality effects in infant chimpanzees were expressed under conditions of emotional arousal. Moreover, degree of laterality may be a predictor of responsivity to stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How cross-fostered chimpanzees ( Pan troglodytes ) initiate and maintain conversations.

This study systematically sampled typical attention-getting sounds and sign language conversations between each of 4 originally cross-fostered chimpanzees (Pan troglodytes), still living freely, but now in a laboratory setting, and a familiar human interlocutor. Videotape records showed that when they encountered a human interlocutor sitting alone at his desk with his back turned to them, the crossfosterlings either left the scene or made attention-getting sounds. The only signs they made to the interlocutor's back were noisy signs. When the human turned and faced them, the chimpanzees promptly signed to him (98% of the time) and rarely made any sounds during the ensuing signed conversations. Under systematic experimental conditions, the signed responses of the chimpanzees were appropriate to the conversational styles of the human interlocutor, confirming daily field observations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical judgments by chimpanzees (Pan troglodytes) in a token economy.

We presented four chimpanzees with a series of tasks that involved comparing two token sets or comparing a token set to a quantity of food. Selected tokens could be exchanged for food items on a one-to-one basis. Chimpanzees successfully selected the larger numerical set for comparisons of 1 to 5 items when both sets were visible and when sets were presented through one-by-one addition of tokens into two opaque containers. Two of four chimpanzees used the number of tokens and food items to guide responding in all conditions, rather than relying on token color, size, total amount, or duration of set presentation. These results demonstrate that judgments of simultaneous and sequential sets of stimuli are made by some chimpanzees on the basis of the numerousness of sets rather than other non-numerical dimensions. The tokens were treated as equivalent to food items on the basis of their numerousness, and the chimpanzees maximized reward by choosing the larger number of items in all situations. (PsycINFO Database Record (c) 2011 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)     

Memory of movies by chimpanzees (Pan troglodytes).

How do animals remember what they see in daily life? The processes involved in remembering such visual information may be similar to those used in interpreting moving images on a monitor. In Experiment 1, 4 adult chimpanzees (Pan troglodytes) were required to discriminate between movies using a movie-to-movie matching-to-sample task. All chimpanzees demonstrated the ability to discriminate movies from the very 1st session onward. In Experiment 2, the ability to retain a movie was investigated through a matching-to-sample task using movie stills. To test which characteristics of movies are relevant to memory, the authors compared 2 conditions. In the continuous condition, the scenes comprising the movie progressed gradually, whereas in the discrete condition, the authors introduced a sudden change from one scene to another. Chimpanzees showed a recency effect only in the discrete condition, suggesting that composition and temporal order of scenes were used to remember the movies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Indexical and referential pointing in chimpanzees (Pan troglodytes).

The spontaneous index finger and other referential pointing in 3 adult, laboratory chimpanzees (Pan troglodytes) who have not received language training is reported. Of 256 total observed points, 254 were emitted in the presence of a human to objects in the environment; therefore, the points were communicative. Indicators of intentional communication used by the subjects included attention-getting behaviors, gaze alternation, and persistence until reward. Thus, pointing by these chimpanzees was intentionally communicative. These data imply that perspective-taking and referential communication are generalized hominoid traits, given appropriate eliciting contexts. Index finger pointing was more frequent with the subjects' dominant hands. This study refutes claims that indexical or referential pointing is species-unique to humans or dependent on linguistic competence or explicit training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual behavior of chimpanzees (Pan troglodytes): Male versus female regulation.

Investigated the sexual behavior of 13 chimpanzees in 2 types of pair tests in order to clarify the interaction of social variables with female hormonal state. The frequency of copulation in tests in which the partners were freely accessible to each other was related to the male's dominance over the female; copulation was less frequent and was related to social compatibility in tests in which the female controlled access. Copulation was related to female hormonal state in both types of test. Results demonstrate (1) an association between female hormonal state and sexual activity of chimpanzees, (2) the influence of social relationships on sexual interactions, and (3) the importance of focusing on female sexual behavior before copulation, rather than copulation per se, in research on sexual arousability of female primates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trading behavior between conspecifics in chimpanzees, Pan troglodytes.

Bartering of commodities between individuals is a hallmark of human behavior that is not commonly seen in other species. This is difficult to explain because barter is mutually beneficial and appears to be within the cognitive capabilities of many species. It may be that other species do not recognize the gains of trade, or that they do not experience conditions (e.g., low risk) in which barter is most beneficial. To answer these questions, the authors instituted a systematic study of chimpanzees’ ability to barter with each other when doing so materially benefited them. Using tokens derived from symbols they had used since infancy, pairs of adult chimpanzees (Pan troglodytes) could trade between themselves to obtain tokens needed to get foods. Chimpanzees flexibly used the tokens to obtain foods from an experimenter; however, they did not spontaneously trade with their partner. After extensive training, chimpanzees engaged in accurate trade behavior as long as an experimenter enforced the structure of the interaction; however, trade between partners disappeared when this enforcement was removed. The authors discuss possible reasons for these findings as well as implications for the evolution of barter across the primate lineage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of spontaneous classificatory behavior in chimpanzees (Pan troglodytes).

Investigated the development of spontaneous classificatory behavior in 5 chimpanzees (Pan troglodytes) tested at different ages and analyzed Ss' spontaneous constructive interactions with sets of logically structured objects. The results show that chimpanzees possess a natural capacity to react to similarities and differences among test stimuli and construct classes. The general progression of their classificatory development is very similar to that reported for human infants from 6 to 24 mo. In both species, classification progresses from constructing single classes by different properties of objects to constructing single classes by similar or identical properties of objects. In addition, like humans, older chimpanzees spontaneously coordinate relations of similarities between sets and construct 2 class-consistent groupings. Chimpanzees' results are compared with those from a similar study with capuchins and macaques. (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)     

Quantity-based interference and symbolic representations in chimpanzees (Pan troglodytes).

Five chimpanzees with training in counting and numerical skills selected between 2 arrays of different amounts of candy or 2 Arabic numerals. A reversed reinforcement contingency was in effect, in which the selected array was removed and the subject received the nonselected candies (or the number of candies represented by the nonselected Arabic numeral). Animals were unable to maximize reward by selecting the smaller array when candies were used as array elements. When Arabic numerals were substituted for the candy arrays, all animals showed an immediate shift to a more optimal response strategy of selecting the smaller numeral, thereby receiving the larger reward. Results suggest that a response disposition to the high-incentive candy stimuli introduced a powerful interference effect on performance, which was effectively overridden by the use of symbolic representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)