A longitudinal study of hand preference in chimpanzees (Pan troglodytes).

A longitudinal study of hand preferences was assessed in a sample of 53 captive chimpanzees. Four measures of laterality assessed during the first 3 months of life were correlated with three measures of hand preferences assessed when the subjects were between 2 and 5 years of age. In addition, the effect of rearing environment on juvenile hand preferences was assessed in a larger sample of 83 chimpanzees. Overall, some early asymmetries were predictive of juvenile hand preferences, notably head orientation and hand-to-hand activities, and a defensive grasping response. No significant effects of rearing on hand preferences were found but males were more right-handed than females for two of the three juvenile measures. The results are discussed within the context of different developmental models of hand preference in humans.

The effects of prenatal drug exposure, term status, and caregiving on arousal and arousal modulation in 8-week-old infants.

Prenatal exposure to cocaine, as well as other drugs, has been linked with "dysregulation," usually defined as problems in arousal and/or behavioral regulation. This study was designed to describe the physiological basis of dysregulation as a function of prenatal cocaine/polydrug exposure and term status. Eight-week-old infants were selected because they are just developing the ability to modulate arousal. One hundred-eighteen infants (23 preterm control, 27 preterm drug-exposed, 29 full-term control, and 39 full-term drug-exposed) completed a protocol during which heart rate (HR) and respiratory rate (RR) were measured. Drug group differences were found in baseline, arousal (response to stress), and arousal modulation (recovery from stress). A hierarchical multiple regression analysis was conducted to determine the portion of variance attributable to postnatal caregiving environment, term status, and specific drug exposure. Term status accounted for significant variance in arousal (both RR and HR), and in arousal modulation (only RR). Prenatal exposure to cocaine contributed a significant amount of unique variance in HR arousal whereas tobacco contributed significantly to HR arousal modulation. Prenatal drug exposure and preterm status contributed differently to dysregulation as measured by physiological responses.

Attentional response at eight weeks in prenatally drug-exposed and preterm infants.

To evaluate the effect of prenatal polydrug exposure on infant attention, 105 8-week-old African-American infants were presented a series of stimuli and their heart rates (HRs) were recorded. Infants were identified postnatally based on mothers' substance use. Four groups were tested: 1) preterm drug-exposed infants (n = 25); 2) full-term, drug-exposed (n = 32); 3) preterm nonexposed (n = 22); and 4) full-term, nonexposed (n = 26). Preterm infants' ages were corrected. Infant's baseline HRs were recorded and then stimuli presented in the following order: auditory (rattle), visual (red ring), and social (examiner's face and voice). There were no HR differences at baseline or in auditory or visual conditions. However, significant differences (F(2, 103) = 6.54, p < 0.01) were seen in response to social stimuli. Drug-exposed infants showed an acceleratory HR indicating distress or arousal and control infants showed a deceleratory response indicating focused attention and there was an interaction due to greater HR response in preterms. Hierarchical regression indicated cocaine (R2 = 0.034, p < 0.05) but not other drug use and instability in parenting (R2 = 0.137, p < 0.001) accounted for the observed differences.

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.

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.

Imitative learning of artificial fruit processing in children (Homo sapiens) and chimpanzees (Pan troglodytes).

Observational learning in chimpanzees and young children was investigated using an artificial fruit designed as an analog of natural foraging problems faced by primates. Each of 3 principal components could be removed in 2 alternative ways, demonstration of only one of which was watched by each subject. This permitted subsequent imitation by subjects to be distinguished from stimulus enhancement. Children aged 2-4 years evidenced imitation for 2 components, but also achieved demonstrated outcomes through their own techniques. Chimpanzees relied even more on their own techniques, but they did imitate elements of 1 component of the task. To our knowledge, this is the first experimental evidence of chimpanzee imitation in a functional task designed to simulate foraging behavior hypothesized to be transmitted culturally in the wild.

Precision grips in young chimpanzees.

A precision grip, thumb-finger opposition, has been regarded as an uniquely human trait. Napier's conclusion that chimpanzees were incapable of precision grip was based on two subjects and prehension of a single object (i.e., a grape). The purpose of the present study was to specify grip type and hand use by 13 young chimpanzees to prehend three different-sized food objects. The subjects were laboratory raised (eight males and five females) and ranged in age from 27 to 58 months. An ethogram was devised that comprised 43 different grip types: ten configurations of precision grips were found, in addition to imprecise or inefficient grip types (nine types), thumb-to-finger opposition (10 types), power grips (two types), and a variety of other grips (12 types). Subjects most often prehended were very small-sized (5 mm × 5 mm × 3 mm) or small-sized (10 mm × 10 mm × 3 mm) food objects with precision and imprecise grips. An analysis of latency to prehend, i.e., efficiency, revealed (1) precision grips were equally efficient for all object sizes; (2) power grips were most efficient with the largest object (a grape); (3) with imprecise grips, the left hand was more efficient than the right with small objects, and with power grips the right hand was more efficient than the left for medium-sized objects. No population handedness was observed, but individual handedness was seen in nine subjects for some grip types and some object sizes. This study provides evidence that young chimpanzees preferentially use a true precision grip to prehend small and very small objects. © 1996 Wiley-Liss, Inc.

Asymmetries in spontaneous head orientation in infant chimpanzees (Pan troglodytes).

Behavioral laterality in head orientation while sleeping in either a supine or prone posture was examined in 43 chimpanzees (Pan troglodytes) for the first 3 months of life. An overall significant right-side lateral bias was found for head orientation in the supine posture. A trend toward greater right-side bias in females compared with males was observed but failed to reach significance. These data suggest that asymmetries in head orientation are present early in life in chimpanzees, and they may be correlated with functional asymmetries observed in adulthood.

Hemispheric specialization in infant chimpanzees (Pan troglodytes): evidence for a relation with gender and arousal.

The current study extends previous documentation of behavioral asymmetries in hand-to-mouth, self-consoling behaviors of infant chimpanzees. The underlying source of lateralized hand-to-mouth, self-calming behavior was investigated by comparing individual differences in neonatal arousal levels, regulatory ability, and motor performance with individual differences in the degree of laterality at 3 months. Asymmetrical hand-to-mouth, self-calming behaviors at 3 months of age were significantly related to general arousal at 2 days of age (i.e., the Range of State cluster scores measured by the Brazelton Neonatal Behavioral Assessment Scale). Simply stated, chimpanzees with a right-hand bias in hand-to-mouth behavior exhibited lower arousal at 2 days of age compared with nonright-handed individuals. The only item of the Range of State cluster to distinguish subjects was irritability: Right-handed subjects were less irritable. Previously, a trend was reported with respect to sex differences in the laterality of hand-to-mouth behavior. With the greater number of subjects in the present study, we found that females exhibited a significantly greater right-hand bias for hand-to-mouth behaviors (12 of 13) than did males (9 of 15). We conclude that neonatal arousability, and not regulatory capacity or motor performance, predicts the degree of laterality found in hand-to-mouth, self-calming behaviors in 3-month-old chimpanzees. These data are discussed from the standpoint of early pari-parturitional or intrauterine factors affecting lateralized development.

Intentional behavior and intentional communication in young free-ranging orangutans.

The goal of this study was to describe the ontogeny of the manipulation of an animate object (i.e., the mother) by young free-ranging orangutans within the context of food sharing. The food-sharing context is an important one in the development of object manipulation skills and social communication. 5 orangutans, ranging in age from 1 month to 5 years, were videotaped with their biological mothers for 18 hours over the course of 9 months. Systematic coding of the videotapes revealed that even young orangutans, 1-6 months old, used intentional (i.e., goal-directed) behaviors. When young orangutans directed behavior toward the mother in addition to the goal object then maternal responses were positive, resulting in the infant obtaining the food. Intentional communication, evident in gestures and consisting of an abbreviated action directed toward the mother, was found in the 3 oldest orangutans (2 1/2, 3 1/2, and 5 years of age). Cognitive competence and behavioral performance are considered from the developmental perspectives of Piaget and prelinguistic communication. The ability to use a communicative gesture as an intermediate means in the coordination of actions on a social agent with actions on an object is evident in young orangutans.

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

Chimpanzees (Pan troglodytes) demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. Twelve young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 years old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2 1/2-year-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-year-old humans.

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.

Behavioral responsiveness to strangers in young chimpanzees (Pan troglodytes).

Earlier studies of responses of primate infants to strangers were frequently confounded with separation from the attachment figure and/or removal to an unfamiliar setting. In the present study, young chimpanzees were tested in a familiar setting with a human female caretaker who served as an attachment figure. Two strangers were introduced: a human female, approximately the size of the caretaker, who refrained from initiating interactions and a larger human male, who repeatedly approached and initiated contact with the subjects. A somewhat more intense response was elicited by the larger, more assertive male stranger, but neither stranger elicited severe distress. The behavior of the chimpanzees is better described as wary, rather than fearful. These results may be attributable to the continued presence of the caretaker in contrast to previous studies reporting severe distress to strangers when chimpanzees are tested alone. A wariness of strangers in nursery-reared chimpanzees may develop by 6 months of age and may diminish somewhat by 2 years of age under the conditions of this study.

Behavioral responsiveness of young chimpanzees (Pan troglodytes) to a novel environment.

Behavioral responsiveness to a novel environment was documented in 22 chimpanzees grouped according to age; 6-months, 1-year, 2-years and 5-years. An attachment figure, a human caretaker, accompanied each subject during the 15-min test sessions so as to preclude confounding of responses to novelty with separation responses. Extreme distress reported previously for chimpanzees and human children when tested alone in a novel situation was rarely observed in these tests when an attachment figure was present. Stereotyped rocking, an indication of mild distress occurred more frequently in the younger animals. Younger animals engaged in distal visual exploration of the environment while remaining close to the attachment figure, whereas the older animals locomoted more frequently and explored the environment directly with their hands. Repeated exposure to the environment reduced the differences among the 6-month, 1-year and 2-year groups. The 6-month group, however, continued to locomote least and least frequently engaged in tactile exploration. These data on chimpanzees resemble data on human children which suggest that an attachment figure: attenuates the distress exhibited by young individuals of these species when exposed to novel stimuli, and thereby provides a secure base which supports the exploration of novel stimuli, a prerequisite to behavioral adaptation.