Intramuscular electrical stimulation of facial muscles in humans and chimpanzees: Duchenne revisited and extended

The pioneering work of Duchenne (1862/1990) was replicated in humans using intramuscular electrical stimulation and extended to another species (Pan troglodytes: chimpanzees) to facilitate comparative facial expression research. Intramuscular electrical stimulation, in contrast to the original surface stimulation, offers the opportunity to activate individual muscles as opposed to groups of muscles. In humans, stimulation resulted in appearance changes in line with Facial Action Coding System (FACS) action units (AUs), and chimpanzee facial musculature displayed functional similarity to human facial musculature. The present results provide objective identification of the muscle substrate of human and chimpanzee facial expressions- data that will be useful in providing a common language to compare the units of human and chimpanzee facial expression.     

Cultural transmission through infant signs: Objects and actions in U.S. and Taiwan

Infant signs are intentionally taught/learned symbolic gestures which can be used to represent objects, actions, requests, and mental state. Through infant signs, parents and infants begin to communicate specific concepts earlier than children’s first spoken language. This study examines whether cultural differences in language are reflected in children’s and parents’ use of infant signs. Parents speaking East Asian languages with their children utilize verbs more often than do English-speaking mothers; and compared to their English-learning peers, Chinese children are more likely to learn verbs as they first acquire spoken words. By comparing parents’ and infants’ use of infant signs in the U.S. and Taiwan, we investigate cultural differences of noun/object versus verb/action bias before children’s first language. Parents reported their own and their children's use of first infant signs retrospectively. Results show that cultural differences in parents’ and children’s infant sign use were consistent with research on early words, reflecting cultural differences in communication functions (referential versus regulatory) and child-rearing goals (independent versus interdependent). The current study provides evidence that intergenerational transmission of culture through symbols begins prior to oral language.     

The development of representational play in chimpanzees and bonobos: Evolutionary implications,pretense, and the role of interspecies communication

This research investigates the development of symbolic or representational play in two species of the genus Pan, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). The participants varied not only by species, but also as to whether they had become proficient in communicating with humans via a set of arbitrary visual symbols, called lexigrams. Using a developmental sequence of representational play based on McCune, we found every level that children manifest to be constructed by Pan. The most robust and regular ontogenetic sequence for both bonobos and chimpanzee was not McCune's five-level progression, but a three-step ontogenetic sequence: Level 1 (no representation, no pretense) precedes Levels 2–4 (representation but no pretense), which in turn precedes Level 5 (includes pretense as well as representation). A linguistic system for interspecies communication was necessary for Level 5 representational play and “true” pretense. Human scaffolding produced developmental progress within sequences for all the apes, except the bonobo who lacked a system of interspecies communication. This evidence suggests that the potential for representational play and its social stimulation were present in the common ancestor of bonobos, chimpanzees and humans five million years ago.     

Recent use of signs by chimpanzees (Pan Troglodytes) in interactions with humans

In light of the controversy about the linguistic properties of chimpanzee signing behavior, the recent sign use of 5 chimpanzees (Pan troglodytes) with long histories of sign use was analyzed while they interacted with longtime human companions. Four corpora from 1992 to 1999 consisting of 3,448 sign utterances were examined. The chimpanzees predominantly used object and action signs. There was no evidence for semantic or syntactic structure in combinations of signs. Longer combinations showed repetition and stringing of object and action signs. The chimpanzees mostly signed with an acquisitive motivation. Requests for objects and actions were the predominant communicative intentions of the sign utterances, though naming and answering also occurred. This recent sign use shows multiple differences with (early) human language.     

Interactive use of sign language by cross-fostered chimpanzees (Pan troglodytes)

Cross-fostered as infants in Reno, Nevada, chimpanzees (Pan troglodytes) Washoe, Moja, Tatu, and Dar freely converse in signs of American Sign Language with each other as well as with humans in Ellensburg, Washington. In this experiment, a human interlocutor waited for a chimpanzee to initiate conversations with her and then responded with 1 of 4 types of probes: general requests for more information, on-topic questions, off-topic questions, or negative statements. The responses of the chimpanzees to the probes depended on the type of probe and the particular signs in the probes. They reiterated, adjusted, and shifted the signs in their utterances in conversationally appropriate rejoinders. Their reactions to and interactions with a conversational partner resembled patterns of conversation found in similar studies of human children.     

Recognition of Line-Drawing Representations by a Chimpanzee (Pan troglodytes)

The ability of a chimpanzee to recognize individuals portrayed in line drawings was evaluated. A 12-year-old female chimpanzee with extensive prior experience in the use of visual symbols matched the line drawings of chimpanzees, humans, and an orangutan with a specific letter of the alphabet. When a line drawing of a familiar individual was presented on the computer screen, the chimpanzee responded by punching a key with the letter of the alphabet that corresponded to the individual's name. Results indicate that the chimpanzee is able to categorize individuals from novel line-drawing representations.     

Acquisition and Transmission of Tool Making and Use for Drinking Juice in a Group of Captive Chimpanzees (Pan troglodytes)

The present study examined the acquisition and transmission of tool making and use in a group of chimpanzees. We set up a piece of apparatus that provided orange juice in an outdoor compound for a group of nine chimpanzees. Although they could reach the juice with their hands, eight of the nine subjects used tools. Fifteen kinds of tools in total were used, such as straw, twigs, and some kinds of leaves. The chimpanzees showed high selectivity with regard to tool type. They preferred to use Thuja occidentalis as a tool although there were 28 species of tree and several kinds of grass available in the compound. Two females initiated the use of the Thuja tool. Since then, five other individuals have begun to use it selectively. Before making the tools by themselves, these five chimpanzees first watched others using the Thuja tool for drinking juice, and then used the Thuja tool which had been used and left by another chimpanzee.     

Conspecific recognition in the chimpanzee (Pan troglodytes): cardiac responses to significant others

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.     

Chimpanzees (Pan troglodytes) remember the location of a hidden food item after altering their orientation to a spatial array

Two chimpanzees (Pan troglodytes) had a direct view of an experimenter placing a food item beneath one of several cups within a horizontal spatial array. The chimpanzees then were required to move around the spatial array, shifting their orientation to the array by 180 degrees . Both chimpanzees remembered the location of the food item. In the next experiment, a visual barrier was placed between the chimpanzees and the spatial array after the food item had been hidden to prevent visual tracking of the location of the object during the chimpanzees' movement. One chimpanzee remembered the location of the hidden item in this variation. These results demonstrate another capacity for spatial memory in this species that complements data indicating chimpanzee spatial memory for invisible displacements, array rotations, and array transpositions.     

Symbolization, language, and chimpanzees: A theoretical reevaluation based on initial language acquisition processes in four young Pan troglodytes

The emergence of symbolic use of word-lexigrams is traced through the course of four experiments with four chimpanzees. The results indicate that it is ill advised to begin language training by introducing the names of objects or their attributes. Training which allowed the subjects to have the machine vend foods, the names of which were on keys, facilitated the discrimination of the lexigrams moreso than did training which called for the labelling of foods held by the experimenter; however, the discriminations so established seemed to be basically associationistic—subjects were not able to use the word symbols appropriately in a communicative manner or to use the words contingent upon the presence or absence of a given food in the dispenser. Subsequent training with verb-object phrases, where the chimpanzees were able to observe all steps in the delivery of foods and drinks contingent upon correct choices among the lexigrams and the formulation of correct requests, fostered the decontextualization of lexigram usage and the symbolic uses of the words used in training. Errorless training procedures were ineffective. By the end of this training the chimpanzees were able to reintegrate and reorganize skills which, initially, had been only partially mastered, and their learning rates of new words and their extended, appropriate use thereof became strongly evidenced. Caution is extended regarding the use of “word” to a response of an ape, be it with a sign of Ameslan, a plastic token, or a lexigram. There are levels of “wordness” and the symbolic, decontextualized level is achieved only through the course of experiences which serve to emphasize the symbol-referent relationship.     

The vindication of the language organ

Ape language research presents us with a worthy and successful example of realist bootstrapping of theorizing and experimentation. In the 1940s, the Hayeses set out without a definition of language, merely taking it that it appeared in the normal maturation of the normal human in normal circumstances and so might appear in a chimpanzee similarly placed. The Gardeners, noting the chimpanzee's limited vocalizing apparatus, tried to show that a chimpanzee would develop language in the same way as the human child if only the language were a sign language. Meshing with research by Premack and Terrace, recent work on fluent human signers of American Sign Language has shown that while chimpanzees can be led to use a gestural pidgin-vocabulary to manipulate and socialize, they in no way develop linguistically as the human infant signer does. In terms of homology, a case can be made that the signing chimpanzees have little improved on the Hayeses' chimpanzee, who eventually vocalized five English words. What this stretch of interaction between theory and experiment bears out is the autonomy of the formal linguistic apparatus from other conceptual and perceptual capacities that we undoubtedly share with our primate cogeners.     

Cues to personality and health in the facial appearance of chimpanzees (Pan troglodytes)

Humans (Homo sapiens) and chimpanzees (Pan troglodytes) can extract socially-relevant information from the static, non-expressive faces of conspecifics. In humans, the face is a valid signal of both personality and health. Recent evidence shows that, like humans, chimpanzee faces also contain personality information, and that humans can accurately judge aspects of chimpanzee personality relating to extraversion from the face alone (Kramer, King, and Ward, 2011). These findings suggest the hypothesis that humans and chimpanzees share a system of personality and facial morphology for signaling socially-relevant traits from the face. We sought to test this hypothesis using a new group of chimpanzees. In two studies, we found that chimpanzee faces contained health information, as well as information of characteristics relating to extraversion, emotional stability, and agreeableness, using average judgments from pairs of individual photographs. In a third study, information relating to extraversion and health was also present in composite images of individual chimpanzees. We therefore replicate and extend previous findings using a new group of chimpanzees and demonstrate two methods for minimizing the variability associated with individual photographs. Our findings support the hypothesis that chimpanzees and humans share a personality signaling system.     

Matching vocalizations to vocalizing faces in a chimpanzee (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

Auditory–visual processing of species-specific vocalizations was investigated in a female chimpanzee named Pan. The basic task was auditory–visual matching-to-sample, where Pan was required to choose the vocalizer from two test movies in response to a chimpanzees vocalization. In experiment 1, movies of vocalizing and silent faces were paired as the test movies. The results revealed that Pan recognized the status of other chimpanzees whether they vocalized or not. In experiment 2, two different types of vocalizing faces of an identical individual were prepared as the test movies. Pan recognized the correspondence between vocalization types and faces. These results suggested that chimpanzees possess crossmodal representations of their vocalizations, as do humans. Together with the ability of vocal individual recognition, this ability might reflect chimpanzees profound understanding of the status of other individuals.     

Communication, symbolic communication, and language: reply to Seidenberg and Petitto

Seidenberg and Petitto's (1987) assertion that Kanzi and Mulika's lexigram usage is not representational is evaluated by contrasting their abilities with Nim's. Kanzi and Mulika's data indicate that they (a) comprehend spoken English words; (b) can identify lexigram symbols when they hear these words; (c) can comprehend lexigram usage; (d) can use lexigrams when referents are absent and can, if asked, lead someone to the referent; and (e) that all these skills were acquired through observation, not conditioning. Nim evidenced no comprehension of signs and could not use signs when referents were absent. He was forced to sign and encouraged to imitate his teachers. Seidenberg and Petitto's negative experiences with Nim apparently led them to overgeneralize to all other apes, regardless of species, modality, or training history. Consequently, they unjustifiably disregard important components of Kanzi and Mulika's comprehension data which demonstrate that their lexical knowledge could not have been acquired in an instrumental fashion.     

Intentional communication in the chimpanzee: The development of deception

Communication about the location of a hidden incentive was studied in chimpanzee-human dyads, in which each member of a pair served alternately as “sender” and “recipient” of information. When the human cooperated with the chimpanzee in finding the goal, from the very beginning the chimpanzees were able to produce and comprehend behavioral cues which conveyed accurate locational information. When the human and chimpanzee competed for the goal, the chimpanzees learned both to withhold information or mislead the recipient, and to discount or controvert the sender's own misleading cues. The chimpanzee's ability to convey and utilize both accurate and misleading information, by taking into account the nature of the sender or recipient, provides evidence of a capacity for intentional communication in this nonhuman primate species.     

Enhanced recognition of emotional stimuli in the chimpanzee (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

Humans often have a better memory of emotional events than neutral events. From the comparative-cognitive perspective, we explored the enhancement of recognition memory by emotion in chimpanzees (Pan troglodytes) using a serial probe recognition task. In this task, we sequentially presented a list of pictures to subjects and then tested their recognition of specific pictures from within the list. We selected pictures of aggressive chimpanzees as emotional stimuli and less tensed, relaxed chimpanzees as neutral stimuli. In Experiment 1, we gave four-item lists to two young chimpanzees; one showed significantly greater recognition of pictures depicting aggressive chimpanzees than neutral ones. In Experiment 2, this chimpanzee was further tested using a recognition task with eight-item lists. The subject again showed better recognition of emotional stimuli than neutral. Furthermore, the presence of an emotional stimulus in the list also facilitated recognition of the neutral item immediately following it. Overall, although only one of the two chimpanzees showed enhanced recognition memory by emotional stimuli, this is the first demonstration of such a response in the chimpanzee. The findings are discussed in comparison with those of human studies.     

Differential use of vocal and gestural communication by chimpanzees (Pan troglodytes) in response to the attentional status of a human (Homo sapiens)

This study examined the communicative behavior of 49 captive chimpanzees (Pan troglodytes), particularly their use of vocalizations, manual gestures, and other auditory- or tactile-based behaviors as a means of gaining an inattentive audience's attention. A human (Homo sapiens) experimenter held a banana while oriented either toward or away from the chimpanzee. The chimpanzees' behavior was recorded for 60 s. Chimpanzees emitted vocalizations faster and were more likely to produce vocalizations as their 1st communicative behavior when a human was oriented away from them. Chimpanzees used manual gestures more frequently and faster when the human was oriented toward them. These results replicate the findings of earlier studies on chimpanzee gestural communication and provide new information about the intentional and functional use of their vocalizations.     

Auditory–visual intermodal matching based on individual recognition in a chimpanzee (Pan troglodytes)

The ability to recognize familiar individuals with different sensory modalities plays an important role in animals living in complex physical and social environments. Individual recognition of familiar individuals was studied in a female chimpanzee named Pan. In previous studies, Pan learned an auditory–visual intermodal matching task (AVIM) consisting of matching vocal samples with the facial pictures of corresponding vocalizers (humans and chimpanzees). The goal of this study was to test whether Pan was able to generalize her AVIM ability to new sets of voice and face stimuli, including those of three infant chimpanzees. Experiment 1 showed that Pan performed intermodal individual recognition of familiar adult chimpanzees and humans very well. However, individual recognition of infant chimpanzees was poorer relative to recognition of adults. A transfer test with new auditory samples (Experiment 2) confirmed the difficulty in recognizing infants. A remaining question was what kind of cues were crucial for the intermodal matching. We tested the effect of visual cues (Experiment 3) by introducing new photographs representing the same chimpanzees in different visual perspectives. Results showed that only the back view was difficult to recognize, suggesting that facial cues can be critical. We also tested the effect of auditory cues (Experiment 4) by shortening the length of auditory stimuli, and results showed that 200 ms vocal segments were the limit for correct recognition. Together, these data demonstrate that auditory–visual intermodal recognition in chimpanzees might be constrained by the degree of exposure to different modalities and limited to specific visual cues and thresholds of auditory cues.     

Teaching apes to ape language: explaining the imitative and nonimitative signing of a chimpanzee (Pan troglodytes)

Fifteen videotaped conversations of a chimpanzee signing with his trainers were examined in order to determine (a) whether the ape was using imitation to learn about new language forms as some human children do and (b) whether the ape's nonimitative utterances implied knowledge of linguistic structures. The answers to both questions were negative. The evidence suggests that the utterances lacked the semantic and syntactic organization found in the utterances of most children. Instead of learning to use signs as symbols for communicating propositional messages, the ape learned to use gestures as nonsymbolic instrumental responses under the stimulus control of objects in the signing context and verbal and nonverbal cues from the trainers. Other research now underway with chimpanzees may eventually reveal whether this performance is characteristic of chimpanzees in general or is the result of particular training strategies used to teach language to chimpanzees.