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Joint attention (JA) is an early manifestation of social cognition, commonly described as interactions in which an infant looks or gestures to an adult female to share attention about an object, within a positive emotional atmosphere. We label this description the JA phenotype. We argue that characterizing JA in this way reflects unexamined assumptions which are, in part, due to past developmental researchers' primary focus on western, middle-class infants and families. We describe a range of cultural variations in caregiving practices, socialization goals, and parenting ethnotheories as an essential initial step in viewing joint attention within inclusive and contextualized perspectives. We begin the process of conducting a decolonized study of JA by considering the core construct of joint attention (i.e., triadic connectedness) and adopting culturally inclusive definitions (labeled joint engagement [JE]). Our JE definitions allow for attention and engagement to be expressed in visual and tactile modalities (e.g., for infants experiencing distal or proximal caregiving), with various social partners (e.g., peers, older siblings, mothers), with a range of shared topics (e.g., representing diverse socialization goals, and socio-ecologies with and without toys), and with a range of emotional tone (e.g., for infants living in cultures valuing calmness and low arousal, and those valuing exuberance). Our definition of JE includes initiations from either partner (to include priorities for adult-led or child-led interactions). Our next foundational step is making an ecological commitment to naturalistic observations (Dahl, 2017, Child Dev Perspect, 11(2), 79-84): We measure JE while infants interact within their own physical and social ecologies. This commitment allows us to describe JE as it occurs in everyday contexts, without constraints imposed by researchers. Next, we sample multiple groups of infants drawn from diverse socio-ecological settings. Moreover, we include diverse samples of chimpanzee infants to compare with diverse samples of human infants, to investigate the extent to which JE is unique to humans, and to document diversity both within and between species. We sampled human infants living in three diverse settings. U.K. infants (n = 8) were from western, middle-class families living near universities in the south of England. Nso infants (n = 12) were from communities of subsistence farmers in Cameroon, Africa. Aka infants (n = 10) were from foraging communities in the tropical rain forests of Central African Republic, Africa. We coded behavioral details of JE from videotaped observations (taken between 2004 and 2010). JE occurred in the majority of coded intervals (Mdn = 68%), supporting a conclusion that JE is normative for human infants. The JA phenotype, in contrast, was infrequent, and significantly more common in the U.K. (Mdn = 10%) than the other groups (Mdn 3%). We found significant within-species diversity in JE phenotypes (i.e., configurations of predominant forms of JE characteristics). We conclude that triadic connectedness is very common in human infants, but there is significant contextualization of behavioral forms of JE. We also studied chimpanzee infants living in diverse socio-ecologies. The PRI/Zoo chimpanzee infants (n = 7) were from captive, stable groups of mixed ages and sexes, and included 4 infants from the Chester Zoo, U.K. and 3 from the Primate Research Institute, Kyoto University, Japan. The Gombe chimpanzee infants (n = 12) were living in a dynamically changing, wild community in the Gombe National Park, Tanzania, Africa. Additionally, we include two Home chimpanzee infants who were reared from birth by a female scientist, in the combined U.S., middle-class contexts of home and university cognition laboratory. JE was coded from videotaped observations (taken between 1993 and 2006). JE occurred during the majority of coded intervals (Mdn = 64%), consistent with the position that JE is normative for chimpanzee infants. The JA phenotype, in contrast, was rare, but more commonly observed in the two Home chimpanzee infants (in 8% and 2% of intervals) than in other chimpanzee groups (Mdns = 0%). We found within-species diversity in the configurations comprising the JE phenotypes. We conclude that triadic connectedness is very common in chimpanzee infants, but behavioral forms of joint engagement are contextualized. We compared JE across species, and found no species-uniqueness in behavioral forms, JE characteristics, or JE phenotypes. Both human and chimpanzee infants develop contextualized social cognition. Within-species diversity is embraced when triadic connectedness is described with culturally inclusive definitions. In contrast, restricting definitions to the JA phenotype privileges a behavioral form most valued in western, middle-class socio-ecologies, irrespective of whether the interactions involve human or chimpanzee infants. Our study presents a model for how to decolonize an important topic in developmental psychology. Decolonization is accomplished by defining the phenomenon inclusively, embracing diversity in sampling, challenging claims of human-uniqueness, and having an ecological commitment to observe infant social cognition as it occurs within everyday socio-ecological contexts. It is essential that evolutionary and developmental theories of social cognition are re-built on more inclusive and decolonized empirical foundations.

Human trafficking has been identified as a global human rights violation. This study aimed to investigate the predictors of prosocial behaviors toward sex-trafficked persons. Participants were 223 undergraduates randomly assigned to read a vignette and answer follow-up questions along with measures of empathy, just world belief, attitudes toward prostitution, and proactive behavior. Empathy was highest for trafficked women, regardless of citizenship status. Trafficked foreign women received the highest empathy, and U.S. prostitutes received the least. Path analysis results indicate just world belief, beliefs about prostitutes, and family values relating to prostitution had direct effects on empathic concern; in turn, empathic concern had a direct effect on proactive behavior. Explanations for the results are discussed, along with educational and clinical implications.

Studies of causal understanding of tool relationships in captive chimpanzees have yielded disparate findings, particularly those reported by Povinelli & colleagues (2000) for tool tasks by laboratory chimpanzees. The present set of experiments tested nine enculturated chimpanzees on three versions of a support task, as described by Povinelli (2000), during which food rewards were presented in different experimental configurations. In Experiment 1, stimulus pairs included a choice between a cloth with a reward on the upper right corner or with a second reward off the cloth, adjacent to a corner, with the second pair comprised of a cloth with food on the upper right corner, and a second cloth with the reward on the substrate, partially covered. All subjects were successful with both test conditions in Experiment 1. In a second study, the experimental choices included one of two possible correct options, paired with one of three incorrect options, with the three incorrect choices all involving varying degrees of perceptual containment. All nine chimpanzees scored significantly above chance across all six conditions. In Experiment 3, four unique conditions were presented, combining one of two possible correct choices with one of two incorrect choices. Six of the subjects scored significantly above chance across the four conditions, and group performance on individual conditions was also significant. Superior performance was demonstrated by female subjects in Experiment 3, similar to sex differences in tool use previously reported for wild chimpanzees and some tool tasks in captive chimpanzees. The present results for Experiments 2 & 3 were significantly differed from those reported by Povinelli et al. (2000) for laboratory-born, peer-reared chimpanzees. One contribution towards the dramatic differences between the two study populations may be the significant rearing and housing differences of the chimpanzee groups. One explanation is that under conditions of enculturation, rich social interactions with humans and conspecifics, as well as active exploration of artifacts, materials, and other aspects of their physical environment had a significant impact on the animals’ ability to recognize the support relationships among the stimulus choices. Overall, the present findings provide strong support for the hypothesis that our chimpanzee subjects based their responses on an understanding of functional support which represented one facet of their folk physics repertoire.

Primates rely on visual attention to gather knowledge about their environment. The ability to recognize such knowledge-acquisition activity in another may demonstrate one aspect of Theory of Mind. Using a series of experiments in which chimpanzees were presented with a choice between an experimenter whose visual attention was available and another whose vision was occluded, we asked whether chimpanzees understood the relationship between visual attention and knowledge states. The animals showed sophisticated understanding of attention from the first presentation of each task. Under more complex experimental conditions, the subjects had more difficulty with species-typical processing of attentional cues and those likely to be learned during human contact. We discuss the results with respect to the comparative impact of enculturation on chimpanzees.

Recent evidence for different tool kits, proposed to be based upon culture-like transmission, have been observed across different chimpanzee communities across Western Africa. In light of these findings, the reported failures by seven captive juvenile chimpanzees tested with 27 tool use tasks (Povinelli 2000) seem enigmatic. Here we report successful performance by a group of nine captive, enculturated chimpanzees, and limited success by a group of six semi-enculturated chimpanzees, on two of the Povinelli tasks, the Flimsy Tool task, and the Hybrid Tool task. All chimpanzees were presented with a rake with a flimsy head and a second rake with a rigid head, either of which could be used to attempt to retrieve a food reward that was out of reach. The rigid rake was constructed such that it had the necessary functional features to permit successful retrieval, while the flimsy rake did not. Both chimpanzee groups in the present experiment selected the functional rigid tool correctly to use during the Flimsy Tool task. All animals were then presented with two "hybrid rakes" A and B, with one half of each rake head constructed from flimsy, non-functional fabric, and the other half of the head was made of wood. Food rewards were placed in front of the rigid side of Rake A and the flimsy side of Rake B. To be successful, the chimps needed to choose the rake that had the reward in front of the rigid side of the rake head. The fully enculturated animals were successful in selecting the functional rake, while the semi-enculturated subjects chose randomly between the two hybrid tools. Compared with findings from Povinelli, whose non-enculturated animals failed both tasks, our results demonstrate that chimpanzees reared under conditions of semi-enculturation could learn to discriminate correctly the necessary tool through trial-and-error during the Flimsy Tool task, but were unable to recognize the functional relationship necessary for retrieving the reward with the "hybrid" rake. In contrast, the enculturated chimpanzees were correct in their choices during both the Flimsy Tool and the Hybrid Tool tasks. These results provide the first empirical evidence for the differential effects of enculturation on subsequent tool use capacities in captive chimpanzees.

Contents: Part I: Empirical Approaches to Counting (or Numerical Competence) in Animals. M. Rilling, Invisible Counting Animals: A History of Contributions from Comparative Psychology, Ethology, and Learning Theory. S.T. Boysen, Counting in Chimpanzees: Nonhuman Principles and Emergent Properties of Number. W.K. Honig, Numerosity as a Dimension of Stimulus Control. D.M. Rumbaugh, D.A. Washburn, Counting by Chimpanzees and Ordinality Judgments by Macaques in Video-Formatted Tasks. Part II:Counting: Criteria and Relations to Basic Processes. H. Davis, Numerical Competence in Animals: Life Beyond Clever Hans. R.K. Thomas, R.B. Lorden, Numerical Competence in Animals: A Conservative View. D.J. Miller, Do Animals Subitize? H.A. Broadbent, R.M. Church, W.H. Meck, B.C. Rakitin, Quantitative Relationships Between Timing and Counting. Part III:Counting in Humans and Animals: Theoretical Perspectives. E.J. Capaldi, Animal Number Abilities: Implications for a Hierarchical Approach to Instrumental Learning. C.R. Gallistel, A Conceptual Framework for the Study of Numerical Estimation and Arithmetic Reasoning in Animals. E. von Glasersfeld, Reflections on Number and Counting. W.A. Wickelgren, Chunking, Familiarity, and Serial Order in Counting.

Displaced reference is the ability to refer to an item that has been moved (displaced) in space and/or time, and has been called one of the true hallmarks of referential communication. Several studies suggest that nonhuman primates have this capability, but a recent experiment concluded that in a specific situation (absent entities), human infants display displaced reference but chimpanzees do not. Here, we show that chimpanzees and bonobos of diverse rearing histories are capable of displaced reference to absent and displaced objects. It is likely that some of the conflicting findings from animal cognition studies are due to relatively minor methodological differences, but are compounded by interpretation errors. Comparative studies are of great importance in elucidating the evolution of human cognition; however, greater care must be taken with methodology and interpretation for these studies to accurately reflect species differences.

The authors previously reported that chimpanzees (Pan troglodytes) showed a striking bias to select the larger of 2 candy arrays, despite a reversed reward contingency in which the animals received the smaller, nonselected array as a reward, except when Arabic numerals were used as stimuli. A perceptual or incentive-based interference occurred that was overcome by symbolic stimuli. The authors of the present study examined the impact of element size in choice arrays, using 1 to 5 large and small candies. Five test-sophisticated chimpanzees selected an array from the 2 presented during each trial. Their responses were not optimal, as animals generally selected arrays with larger total mass; thus, they received the smaller remaining array as a reward. When choice stimuli differed in size and quantity, element size was more heavily weighted, although choices reflected total candy mass. These results replicate previous findings showing chimpanzees' difficulties with quantity judgments under reverse reward contingencies and also show that individual item size exerts a more powerful interference effect.

Nonhuman primates represent the most significant extant species for comparative studies of cognition, including such complex phenomena as numerical competence, among others. Studies of numerical skills in monkeys and apes have a long, though somewhat sparse history, although questions for current empirical studies remain of great interest to several fields, including comparative, developmental, and cognitive psychology; anthropology; ethology; and philosophy, to name a few. In addition to demonstrated similarities in complex information processing, empirical studies of a variety of potential cognitive limitations or constraints have provided insights into similarities and differences across the primate order, and continue to offer theoretical and pragmatic directions for future research. An historical overview of primate numerical studies is presented, as well as a summary of the 17-year research history, including recent findings, of the Comparative Cognition Project at The Ohio State University Chimpanzee Center. Overall, the archival literature on number-related skills and counting in nonhuman primates offers important implications for revising our thinking about comparative neuroanatomy, cross-species (human/ape) cognitive similarities and differences, and the evolution of cognition represented by the primate continuum.

Six chimpanzees (Pan troglodytes) were presented with pairs of color photographic images of 5 different categories of animals (cat, chimp, gorilla, tiger, fish). The subjects responded to each pair using symbols for "same" and "different." Both within- and between-category discriminations were tested, and all chimpanzees classified the image pairs in accordance with the 5 experimenter-defined categories under conditions of nondifferential reinforcement. Although previous studies have demonstrated identification or discrimination of natural categories by nonhuman animals, subjects were typically differentially reinforced for their responses. The present findings demonstrate that chimpanzees can classify natural objects spontaneously and that such classifications may be similar to those that would be observed in human subjects.

We previously reported that chimpanzees were unable to optimally select the smaller of two candy arrays in order to receive a larger reward. When Arabic numerals were substituted for the candy arrays, animals who had had prior training with numerical symbols showed an immediate and significant improvement in performance and were able to select reliably the smaller numeric representation in order to obtain a larger reward. Poor performance with candy arrays was interpreted as reflecting a response bias toward the intrinsic incentive and/or perceptual features of the larger array. In contrast, the Arabic numerals represent numerosity symbolically and appear to promote response choice on the basis of abstract processing of numerosity, with minimal interference from the inherent properties of the choice stimuli. The present study tested the hypothesis that, for mixed symbol-candy choice pairs, the requisite processing of the abstract numeral may foster a mode of numerical judgment that diminishes the interfering incentive/perceptual effects of the candy stimuli. The results were consistent with this hypothesis. Whereas performance on candy-candy arrays was significantly below chance levels, performance on numeral-candy choice pairs was significantly above chance and comparable with performance on numeral-numeral pairs.

Researchers investigating the evolutionary roots of human culture have turned to comparing behaviours across nonhuman primate communities, with tool-based foraging in particular receiving much attention. This study examined whether natural extractive foraging behaviours other than tool selection differed across nonhuman primate colonies that had the same foods available. Specifically, the behaviours applied to open the hard-shelled fruits of Strychnos spp. were examined in three socially separate, semi-wild colonies of chimpanzees (Pan troglodytes) that lived under shared ecological conditions at Chimfunshi Wildlife Orphanage, and were comparable in their genetic makeup. The chimpanzees (N = 56) consistently applied six techniques to open these fruits. GLMM results revealed differences in the number of combined technique types to open fruits across the colonies. They also showed colony differences in the application of three specific techniques. Two techniques (full biting and fruit cracking) were entirely absent in some colonies. This study provides empirical evidence that natural hard-shelled fruit-opening behaviours are distinct across chimpanzee colonies, differences that most likely have not resulted from ecological and genetic reasons.

Five chimpanzees (Pan troglodytes) were tested to assess their understanding of causality in a tool task. The task consisted of a transparent tube with a trap-hole drilled in its middle. A reward was randomly placed on either side of the hole. Depending on which side the chimpanzee inserted the stick into, the candy was either pushed out of the tube or into the trap. In Experiment 1, the success rate of 2 chimpanzees rose highly above chance, but that of the other subjects did not. Results show that the 2 successful chimpanzees selected the correct side for insertion beforehand. Experiment 2 ruled out the possibility that their success was due to a distance-based associative rule, and the results favor an alternative hypothesis that relates success to an understanding of the causal relation between the tool-using action and its outcome.

The burgeoning literature on numerical skills, counting and quantity judgements by animals over the past two decades attests that the long shadow of Clever Hans has finally dissipated. Not only have the types of tasks expanded, but the number of species, particularly those outside the mammalian order, is beginning to become more diverse. The primate order has been well represented, including studies with capuchin monkeys (Judge, Evans and Vyas, 2005), cotton-top tamarins (Uller, Hauser and Carey, 2001), rhesus monkeys (Beran, 2001, 2007a, b; Brannon and Terrace, 1998; Cantlon and Brannon, 2006; Hauser, Carey and Hauser, 2000); squirrel monkeys (Thomas and Chase, 1980; Terrell and Thomas, 1990), chimpanzees (Beran and Beran, 2004; Beran, Evans and Harris, 2008; Biro and Matsuzawa, 2001; Boysen and Berntson, 1989; Matsuzawa, 1984; Tomanaga, 2008), gorillas (Hanus and Call, 2007) and orang-utans (Call, 2000). However, some of the most interesting new studies have explored numerical questions with such disparate species as salamanders (Uller et al., 2003), chickens (Abeyesinghe et al., 2005), parrots (Pepperberg, 1994; Vick and Bouvet, in press), horses (Uller and Lewis, 2009), pigeons (Emmerton, Lohmann and Neimann, 1997; Roberts, 2005), mangabey monkeys (Albaich-Serrano, Guillen-Salazar and Call, 2007), cotton-top tamarins (Kralik, 2005), dolphins (Kilian et al., 2003), dogs (West and Young, 2002), sea lions (Gentry and Roeder, 2006; Gentry, Palmier and Roeder, 2004), cleaner wrasse fish (Danisman, Bshary and Bergmuller, 2010) and mosquitofish (Agrillo, Dadda and Bisazza, 2007).

The principle of evaluative bivalence asserts that behavioral processes often organize along the evaluative dimension, due to a fundamental pattern of bivalent neurobehavioral organization extending throughout the neuraxis. This principle offers a powerful approach to the explication of complex behavioral relationships and the integration of diverse literatures. It also offers a guiding conceptual framework for the study of neurobehavioral relationships which holds the promise of integrating rather than diversifying the study of neural mechanisms for disparate behavioral phenomena.

Three chimpanzees (Pan troglodytes) were trained to discriminate among pairs of boxes in an ABCDE-ordered series. The 2nd member of each pair was reinforced, until all 4 training pairs were learned. During novel tests the nonadjacent BD pair was presented, and all 3 animals reliably selected D. In Experiment 2, numerals 1-5 served as stimuli. One chimpanzee reliably selected the larger numeral 4 during testing with a nonadjacent pair (2-4), and 2 chimps showed no preference. In a 2nd phase, the same chimp demonstrated proficiency at reversing the task, reliably selecting the smaller of the 2-4 pair. In Experiment 4, after additional training, a 2nd test, which included novel test pairs composed of numbers that had not been used during training, was completed. Two of 3 animals were 100% correct on Trial 1 for all novel pairs. The results suggest that chimpanzees with experience in number concepts may recognize the ordinal character of numbers.

Four chimpanzees, Pan troglodytes, were individually trained to cooperate with a human partner on a task that allowed both participants to obtain food rewards. In each chimpanzee-human dyad, one of the participants (the informant) could see which pair of food trays on a four-choice apparatus was baited, but had no means of obtaining it. The other participant (the operator) could pull one of four handles to bring a pair of the trays within reach of both participants, but could not see which choice was correct. Two of the chimpanzees were initially trained as informants and adopted spontaneous gestures to indicate the location of the food. The two other chimpanzees were trained as operators and learned to respond to the pointing of their human partner. After the chimpanzee subjects reached near perfect performance, the roles in each chimpanzee-human dyad were reversed. Three of the four chimpanzees showed immediate evidence of comprehension of their new social role. The results are discussed in the context of cognitive empathy and the potential for future research on social attribution in non-human primates.

Nine chimpanzees (Pan troglodytes) were tested for their ability to assemble or disassemble the appropriate tool to obtain a food reward from two different apparatus. In its deconstructed form, the tool functioned as a probe for one apparatus. In its constructed form, the tool functioned as a hook, appropriate for a second apparatus. Each subject completed four test trials with each apparatus type. Tool types were randomized and counter-balanced between the two forms. Results demonstrated that adult and juvenile chimpanzees (N = 7) were successful with both tool types, while two infant chimpanzees performed near chance. Off-line video analyses revealed that tool modifications followed by attempted solutions by the adults and juveniles were typically correct on the first attempt. Neither infant was successful in modifying tools correctly on the first attempt over all eight trials. The older chimpanzees’ ability to modify the appropriate tool consistently prior to use indicates an immediate recognition of the functional attributes necessary for the successful use of tool types on each apparatus, and represents a non-replication of a previously reported study by Povinelli.

In the present study, the contributions of spatial and object features to chimpanzees' comprehension of scale models were examined. Seven chimpanzees that previously demonstrated the ability to use a scale model as an information source for the location of a hidden item were tested under conditions manipulating the feature correspondence and spatial-relational correspondence between objects in the model and an outdoor enclosure. In Experiment 1, subjects solved the task under two conditions in which one object cue (color or shape) was unavailable, but positional cues remained. Additionally, performance was above chance under a third condition in which both types of object cues, but not position cues, were available. In Experiment 2, 2 subjects solved the task under a condition in which shape and color object cues were simultaneously unavailable. The results suggest that, much like young children, chimpanzees are sensitive to both object and spatial-relational correspondences between a model and its referent.

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.

We describe the first brain event-related potential (ERP) study of cognitive processes in the chimpanzee. In an extension of our studies on the ontogeny of vocal perception, ERP measures were obtained during the presentation of simple nonsignal stimuli as well as conspecific and human vocalizations. We initially confirmed findings from humans and monkeys of the appearance of a longlatency positivity in the ERP waveform to a rare stimulus in an oddball paradigm. This ERP component is reminiscent of the P3a reported in humans under similar (passive) experimental conditions. We further demonstrated that both conspecific and human vocal stimuli having affective significance also enhanced late positive components of the ERP. These late positive components displayed a predominant fronto–central distribution, with a maxima at Cz. Additionally, responses to adaptively significant vocal stimuli showed a right hemisphere laterality, whereas no significant laterality was observed with the rare stimulus in the oddball paradigm. Results document the feasibility of ERP measures in chimpanzees and their potential utility in the study of the ontogeny and phylogeny of vocal perception. © 1993 John Wiley & Sons, Inc.

Estimation of quantity and/or related phenomena (e.g., estimation of time) have been demonstrated in a variety of species. Numerous hypotheses have been proposed to account for a range of behaviors observed in rats, raccoons, various species of birds, rhesus monkeys, and chimpanzees relative to the emergence of counting skills in children. An understanding of the cognitive processes that underlie numerical skills in nonhuman animals could provide information critical to clarifying the evolution of cognitive capabilities. Capaldi and Miller (1988) suggested that despite opportunities to employ other strategies for task solution, animals readily use counting cues to solve a variety of instrumental problems. Capaldi and his colleagues further proposed that counting mechanisms may explain a wide range of learning situations in rats and other mammals. In contrast, Davis and Memmott (1982) proposed that animals engage in counting as a last-resort strategy and questioned the evolutionary significance of such capacities, given that these behaviors often require intensive training in a highly structured laboratory situation (e.g., Davis, 1984; Ferster, 1964). The degree to which counting behaviors in nonhuman species fit the criteria for true counting, as defined for children (Gelman & Gallistel, 1978), is a point of controversy (Davis & Perusse, 1988). Interestingly, discussion of related issues pervades the human developmental literature (e.g., Gelman & Gallistel, 1978; Piaget, 1952), including the age at which children are capable of demonstrating counting, as opposed to subitizing (Beckmann, 1924; Mandler & Shebo, 1981), that is, the proposed ability to estimate small numbers of items in an array through a direct perceptual apprehension mechanism (von Glasersfeld, 1982).

A rational strategy for the automated detection of artifacts in heart period data is outlined and evaluated. The specific implementation of this approach for heart period data is based on the distribution characteristics of successive heart period differences. Because beat-to-beat differences generated by artifacts are large, relative to normal heart period variability, extreme differences between successive heart periods serve to identify potential artifacts. Critical to this approach are: 1) the derivation of the artifact criterion from the distribution of beat differences of the individual subject, and 2) the use of percentile-based distribution indexes, which are less sensitive to corruption by the presence of artifactual values than are least-squares estimates. The artifact algorithms were able to effectively identify artifactual beats embedded in heart period records, flagging each of the 1494 simulated and actual artifacts in data sets derived from both humans and chimpanzees. At the same time, the artifact algorithms yielded a false alarm rate of less than 0.3%. Although the present implementation was restricted to heart period data, the outlined approach to artifact detection may also be applicable to other biological signals.

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.

Primate Origins of Human Cognition and Behavior . T. Matsuzawa, Ed. Springer, Tokyo, 2001. 599 pp. $129, €119, ¥9,500. ISBN 4-431-70290-3. In a volume that highlights Japanese contributions to primatology, Matsuzawa and his colleagues explore a broad range of topics from the fields of behavioral ecology, psychology, and cognitive science.

The ability of a chimpanzee (Pan troglodytes) to recognize photographs of conspecifics was evaluated with heart-rate measures. Heart rate was recorded before, during, and after viewing photographs of an aggressive chimpanzee, a friendly companion animal, and an unfamiliar chimpanzee. The subject displayed a differential pattern of heart-rate response to the stimulus animals, without prior experience with the photographs. Responses to the aggressive animal were acceleratory, which suggests a defensive response. Respiratory sinus arrhythmia suggested that this response was associated with sympathetic activation. In contrast, responses to the familiar animal were minimal, whereas cardiac deceleration was observed in response to the strange chimp, which likely reflects an orienting response. Results suggest the chimpanzee is able to recognize photographs of individual conspecifics and that heart-rate change can reflect the nature of established social relationships between chimpanzees.

Tonic and phasic measures of heart rate were obtained during vigilance performance in a chimpanzee. Results revealed that patterns of cardiac activity are correlated with critical dimensions of performance, and are highly comparable to those of human subjects. Baseline heart rate decreased within individual sessions and increased over sessions, in close correspondence to progressive trends in reaction time. Heart period variability also covaried with reaction time, faster reaction time being associated with both higher heart rate and lower heart period variability. Phasic patterns of cardiac activity, however, appeared to relate more specifically to performance variables than did baseline measures. Target detection was followed by notable cardiac acceleration, whereas misses, correct rejections, and false alarms were associated with heart rate decelerations. The cardiac acceleration to target detection appeared not to result simply from a feedback consequence of the motor response, but rather to reflect aspects of the detection process. Finally, target stimuli were detected more frequently when they occurred after a long heart period. This did not reflect an effect of baseline heart rate, since the probability of target detection did not covary with changes in baseline heart rate. Rather, the results are more consistent with the view that temporal fluctuations in an attentional or preparatory state are reflected in transient variations in heart period.

Three chimpanzees (Pan troglodytes) were provided with 18 different stimulus pages for drawing. The resulting 618 drawings were coded for drawn marks, and results were compared with early reports on ape drawing (Morris, 1962; Schiller, 1951) and with more recent systematic studies (Smith, 1973). The findings of the present study confirm Smith's observations of a tendency for the animals to draw closer to the center and toward the bottom of the page. No evidence for perceptual balancing was observed in drawings produced on pages with lateral figures, nor was any evidence for closure apparent with complex figures. The present results agree with earlier findings that chimpanzees will engage in drawing activities without training or reinforcement, and this behavior may reflect their intrinsic interest in exploratory and manipulative play.