Natural imitation induced by joint attention in Japanese monkeys

Action imitation via trajectory-based or posture-based planning

Imitation is a significant daily activity involved in social interaction and motor learning. Imitation has been theorized to be performed in at least two ways. In posture-based imitation, individuals reproduce how the body should look and feel, and are sensitive to the relative positioning of body parts. In trajectory imitation, individuals mimic the spatiotemporal motion path of the end effector. There are clear anecdotal situations in which one might benefit from imitating postures (when learning ballet) or trajectories (when learning to reach around objects). However, whether these are in fact distinct methods of imitation, and if so, whether they may be applied interchangeably to perform the same task, remain unknown. If these are indeed separate mechanisms that rely on different computational and neural resources, a cost should be incurred when switching from using one mechanism to the other within the context of a single task. Therefore, observing a processing cost would both provide evidence that these are indeed two distinct mechanisms, and that they may be used interchangeably when trying to imitate the same stimulus. To test this, twenty-five healthy young adults performed a sequential multitasking imitation task. Participants were first instructed to pay attention to the limb postures or the hand path of a video-recorded model, then performed a neutral, congruent, or incongruent intervening motor task. Finally, participants imitated the modeled movement. We examined both spatial and temporal imitation accuracy as well as individual spatial consistency. When the primary task involved imitating trajectories, analysis of individual consistency suggested a processing cost: movements following the posture-matching intervening task were less consistent with baseline (neutral) performance, suggesting performance may be disrupted by the incongruence. This effect was not observed when imitating limb postures. In summary, we present initial evidence for a difference between posture matching and trajectory imitation as a result of instructions and intervening tasks that is consistent with the existence of two computationally distinct imitation mechanisms.

Performance monitoring in the medial frontal cortex and related neural networks: From monitoring self actions to understanding others' actions

Action is a key channel for interacting with the outer world. As such, the ability to monitor actions and their consequences - regardless as to whether they are self-generated or other-generated - is of crucial importance for adaptive behavior. The medial frontal cortex (MFC) has long been studied as a critical node for performance monitoring in nonsocial contexts. Accumulating evidence suggests that the MFC is involved in a wide range of functions necessary for one's own performance monitoring, including error detection, and monitoring and resolving response conflicts. Recent studies, however, have also pointed to the importance of the MFC in performance monitoring under social conditions, ranging from monitoring and understanding others' actions to reading others' mental states, such as their beliefs and intentions (i.e., mentalizing). Here we review the functional roles of the MFC and related neural networks in performance monitoring in both nonsocial and social contexts, with an emphasis on the emerging field of a social systems neuroscience approach using macaque monkeys as a model system. Future work should determine the way in which the MFC exerts its monitoring function via interactions with other brain regions, such as the superior temporal sulcus in the mentalizing system and the ventral premotor cortex in the mirror system.

Development of social systems neuroscience using macaques

This paper reviews the literature on social neuroscience studies using macaques in the hope of encouraging as many researchers as possible to participate in this field of research and thereby accelerate the system-level understanding of social cognition and behavior. We describe how different parts of the primate brain are engaged in different aspects of social information processing, with particular emphasis on the use of experimental paradigms involving more than one monkey in laboratory settings. The description begins with how individual neurons are used for evaluating socially relevant information, such as the identity, face, and focus of attention of others in various social contexts. A description of the neural bases of social reward processing and social action monitoring follows. Finally, we provide several perspectives on novel experimental strategies to help clarify the nature of interacting brains under more socially and ecologically plausible conditions.

Learning by observation in the macaque monkey under high experimental constraints

While neuroscience research has tremendously advanced our knowledge about the neural mechanisms of individual learning, i.e. through trial-and-error, it is only recently that neuroscientists have begun to study observational learning, and thus little is known about its neural mechanisms. One limitation is that observational learning has been addressed under unconstrained experimental conditions, not compatible with neuronal recordings. This study examined observational learning in macaque monkeys under the constraining conditions of behavioral neurophysiology. Two animals sat in primate chairs facing each other, with their head fixed. A touch screen was placed face up between the chairs at arm's reach, and the monkeys were trained on an abstract visuomotor associative task. In one experiment, the monkeys alternated the roles of "actor" and "observer". The actor learned to associate visual cues with reaching targets, while the observer "watched" freely. Then, the observer was given the same cue-target associations just performed by the actor, or had to learn new, not previously observed ones. The results show that learning performance is better after observation. In experiment 2, one monkey learned from a human actor who performed the task with errors only, or with successes only in separate blocks. The monkey's gain in performance was higher after observation of errors than after successes. The findings suggest that observational learning can occur even under highly constraining conditions, and open the way for investigating the neuronal correlates of social learning using the methods of behavioral neurophysiology.

Macaque monkeys can learn token values from human models through vicarious reward

Monkeys can learn the symbolic meaning of tokens, and exchange them to get a reward. Monkeys can also learn the symbolic value of a token by observing conspecifics but it is not clear if they can learn passively by observing other actors, e.g., humans. To answer this question, we tested two monkeys in a token exchange paradigm in three experiments. Monkeys learned token values through observation of human models exchanging them. We used, after a phase of object familiarization, different sets of tokens. One token of each set was rewarded with a bit of apple. Other tokens had zero value (neutral tokens). Each token was presented only in one set. During the observation phase, monkeys watched the human model exchange tokens and watched them consume rewards (vicarious rewards). In the test phase, the monkeys were asked to exchange one of the tokens for food reward. Sets of three tokens were used in the first experiment and sets of two tokens were used in the second and third experiments. The valuable token was presented with different probabilities in the observation phase during the first and second experiments in which the monkeys exchanged the valuable token more frequently than any of the neutral tokens. The third experiments examined the effect of unequal probabilities. Our results support the view that monkeys can learn from non-conspecific actors through vicarious reward, even a symbolic task like the token-exchange task.

Vicarious learning from human models in monkeys

We examined whether monkeys can learn by observing a human model, through vicarious learning. Two monkeys observed a human model demonstrating an object–reward association and consuming food found underneath an object. The monkeys observed human models as they solved more than 30 learning problems. For each problem, the human models made a choice between two objects, one of which concealed a piece of apple. In the test phase afterwards, the monkeys made a choice of their own. Learning was apparent from the first trial of the test phase, confirming the ability of monkeys to learn by vicarious observation of human models.

Cognitive consequences of cooperative breeding in primates?

Several hypotheses propose that cooperative breeding leads to increased cognitive performance, in both nonhuman and human primates, but systematic evidence for such a relationship is missing. A causal link might exist because motivational and cognitive processes necessary for the execution and coordination of helping behaviors could also favor cognitive performance in contexts not directly related to caregiving. In callitrichids, which among primates rely most strongly on cooperative breeding, these motivational and cognitive processes include attentional biases toward monitoring others, the ability to coordinate actions spatially and temporally, increased social tolerance, increased responsiveness to others' signals, and spontaneous prosociality. These processes are likely to enhance performance particularly in socio-cognitive contexts. Therefore, cooperatively breeding primates are expected to outperform their independently breeding sister taxa in socio-cognitive tasks. We evaluate this prediction by reviewing the literature and comparing cognitive performance in callitrichids with that of their sister taxa, i.e. squirrel monkeys, which are independent breeders, and capuchin monkeys, which show an intermediate breeding system. Consistent with our prediction, this review reveals that callitrichids systematically and significantly outperform their sister taxa in the socio-cognitive, but not in the non-social domain. This comparison is complemented with more qualitative evaluations of prosociality and cognitive performance in non-primate cooperative breeders, which suggest that among mammals, cooperative breeding generally produces conditions conducive to socio-cognitive performance. In the hominid lineage, however, the adoption of extensive allomaternal care presumably resulted in more pervasive cognitive consequences, because the motivational consequences of cooperative breeding was added to an ape-level cognitive system already capable of understanding simple mental states, which enabled the emergence of shared intentionality.

Culture in the mind's mirror: how anthropology and neuroscience can inform a model of the neural substrate for cultural imitative learning

Cultural neuroscience, the study of how cultural experience shapes the brain, is an emerging subdiscipline in the neurosciences. Yet, a foundational question to the study of culture and the brain remains neglected by neuroscientific inquiry: "How does cultural information get into the brain in the first place?" Fortunately, the tools needed to explore the neural architecture of cultural learning - anthropological theories and cognitive neuroscience methodologies - already exist; they are merely separated by disciplinary boundaries. Here we review anthropological theories of cultural learning derived from fieldwork and modeling; since cultural learning theory suggests that sophisticated imitation abilities are at the core of human cultural learning, we focus our review on cultural imitative learning. Accordingly we proceed to discuss the neural underpinnings of imitation and other mechanisms important for cultural learning: learning biases, mental state attribution, and reinforcement learning. Using cultural neuroscience theory and cognitive neuroscience research as our guides, we then propose a preliminary model of the neural architecture of cultural learning. Finally, we discuss future studies needed to test this model and fully explore and explain the neural underpinnings of cultural imitative learning.

Imitation of body movements facilitated by joint attention through eye contact and pointing in Japanese monkey

Eye contact and pointing are typical gestures in order to direct another individual's attention toward a target. We previously investigated on Japanese monkeys whether joint attention ability encouraged by eye contact and pointing was associated with the imitation of human's actions. The monkeys with the joint attention skills showed the imitation of human's actions. In the current study, we investigated on a monkey whether joint attention ability also facilitated the imitation of human body-movements. Results showed that the monkey being taught eye contact and pointing showed the imitation of human body-movements. These results suggest that the monkeys have basic potential for following another individual's motion, and that what imitation expresses depends on where the monkeys are paying attention. Thus, eye contact and pointing are suitable for directing the monkey's attention toward the human.

Aplasics Born without Hands Mirror the Goal of Hand Actions with Their Feet

The premotor and parietal mirror neuron system (MNS) is thought to contribute to the understanding of observed actions by mapping them onto "corresponding" motor programs of the observer [1-24], but how would the MNS respond to the observation of hand actions if the observer never had hands? Would it not show changes of blood-oxygen-level dependent (BOLD) signal, because the observer lacks motor programs that can resonate [12, 25, 26], or would it show significant changes because the observer has motor programs for the foot or mouth with corresponding goals [15, 17, 19, 27, 28]? We scanned two aplasic subjects, born without arms or hands, while they watched hand actions and compared their brain activity with that of 16 control subjects. All subjects additionally executed actions with different effectors (feet, mouth, and, for controls, hands). The BOLD signal of aplasic individuals within the putative MNS was augmented when they watched hand actions, demonstrating the brain's capacity to mirror actions that deviate from the embodiment of the observer by recruiting voxels involved in the execution of actions that achieve corresponding goals by different effectors. This sheds light on the functional organization of the MNS and predominance of goals in imitation.

Learning by observation in rhesus monkeys

Habit memory provides us with a vast repertoire of learned rules, including stimulus-reward associations, that ensures fast and adapted decision making in daily life. Because we share this ability with monkeys, lesion and recording studies in rhesus macaques have played a key role in understanding the neural bases of individual trial-and-error habit learning. Humans, however, can learn new rules at a lower cost via observation of conspecifics. The neural properties underlying this more ecological form of habit learning remain unexplored, and it is unclear whether the rhesus macaque can be a useful model in this endeavor. We addressed this issue by testing four monkeys from the same social group in their usual semi-natural habitat using a well-established marker of habit memory, concurrent discrimination learning. Each monkey learned 24 lists of 10 object-reward associations each. For one list out of two, monkeys could observe the testing session of another member of the group prior to being tested with the same list themselves. Learning was faster for these lists than for those learned solely by trial-and-error. Errors to criterion (9/10 correct responses) were reduced by 39%, and faultless performance could be achieved for up to 5 of the 10 pairs. These data demonstrate that rhesus macaques spontaneously observe a conspecific learning new stimulus-reward associations, and substantially benefit from this observation. They ascertain that the neural underpinnings of socially-mediated forms of habit learning can be explored using the powerful tools of monkey research, including neurophysiological recordings.

Neonatal imitation in rhesus macaques

The emergence of social behaviors early in life is likely crucial for the development of mother–infant relationships. Some of these behaviors, such as the capacity of neonates to imitate adult facial movements, were previously thought to be limited to humans and perhaps the ape lineage. Here we report the behavioral responses of infant rhesus macaques (Macaca mulatta) to the following human facial and hand gestures: lip smacking, tongue protrusion, mouth opening, hand opening, and opening and closing of eyes (control condition). In the third day of life, infant macaques imitate lip smacking and tongue protrusion. On the first day of life, the model's mouth openings elicited a similar matched behavior (lip smacking) in the infants. These imitative responses are present at an early stage of development, but they are apparently confined to a narrow temporal window. Because lip smacking is a core gesture in face-to-face interactions in macaques, neonatal imitation may serve to tune infants' affiliative responses to the social world. Our findings provide a quantitative description of neonatal imitation in a nonhuman primate species and suggest that these imitative capacities, contrary to what was previously thought, are not unique to the ape and human lineage. We suggest that their evolutionary origins may be traced to affiliative gestures with communicative functions.

This manuscript provides the first quantitative description of neonatal imitation in a nonhuman primate, indicating imitative capacities are not unique to the ape and human lineage, contrary to what was previously thought.

The neural origins and implications of imitation, mirror neurons and tool use

Several recent studies report how laboratory-raised, non-human primates exposed to tool use can exhibit intelligent behaviors, such as imitation and reference vocal control, that are never seen in their wild counterparts. Tool-use training appears to forge a novel cortico-cortical connection that underlies this boost in capacity, which normally exists only as latent potential in lower primates. Although tool-use training is patently non-naturalistic, its marked effects on brain organization and behavior could shed light on the evolution of higher intelligence in humans.

Cortical memory mechanisms and language origins

We have previously proposed that cortical auditory-vocal networks of the monkey brain can be partly homologized with language networks that participate in the phonological loop. In this paper, we suggest that other linguistic phenomena like semantic and syntactic processing also rely on the activation of transient memory networks, which can be compared to active memory networks in the primate. Consequently, short-term cortical memory ensembles that participate in language processing can be phylogenetically tracked to more simple networks present in the primate brain, which became increasingly complex in hominid evolution. This perspective is discussed in the context of two current interpretations of language origins, the "mirror-system hypothesis" and generativist grammar.

Mirror neurons and imitation: A computationally guided review

Neurophysiology reveals the properties of individual mirror neurons in the macaque while brain imaging reveals the presence of 'mirror systems' (not individual neurons) in the human. Current conceptual models attribute high level functions such as action understanding, imitation, and language to mirror neurons. However, only the first of these three functions is well-developed in monkeys. We thus distinguish current opinions (conceptual models) on mirror neuron function from more detailed computational models. We assess the strengths and weaknesses of current computational models in addressing the data and speculations on mirror neurons (macaque) and mirror systems (human). In particular, our mirror neuron system (MNS), mental state inference (MSI) and modular selection and identification for control (MOSAIC) models are analyzed in more detail. Conceptual models often overlook the computational requirements for posited functions, while too many computational models adopt the erroneous hypothesis that mirror neurons are interchangeable with imitation ability. Our meta-analysis underlines the gap between conceptual and computational models and points out the research effort required from both sides to reduce this gap.

A comparative analysis of animals' understanding of the human pointing gesture

We review studies demonstrating the ability of some animals to understand the human pointing gesture. We present a 3-step analysis of the topic. (1) We compare and evaluate current experimental methods (2) We compare available experimental results on performance of different species and investigate the interaction of species differences and other independent variables (3) We evaluate how our present understanding of pointing comprehension answers questions about function, evolution and mechanisms. Recently, a number of different hypotheses have been put forward to account for the presence of this ability in some species and for the lack of such comprehension in others. In our view, there is no convincing evidence for the assumption that the competitive lifestyles of apes would inhibit the utilization of this human gesture. Similarly, domestication as a special evolutionary factor in the case of some species falls short in explaining high levels of pointing comprehension in some non-domestic species. We also disagree with the simplistic view of describing the phenomenon as a simple form of conditioning. We suggest that a more systematic comparative research is needed to understand the emerging communicative representational abilities in animals that provide the background for comprehending the human pointing gesture.

The motor theory of social cognition: a critique

Recent advances in the cognitive neuroscience of action have considerably enlarged our understanding of human motor cognition. In particular, the activity of the mirror system, first discovered in the brain of non-human primates, provides an observer with the understanding of a perceived action by means of the motor simulation of the agent's observed movements. This discovery has raised the prospects of a motor theory of social cognition. In humans, social cognition includes the ability to mindread, and many motor theorists of social cognition try to bridge the gap between motor cognition and mindreading by endorsing a simulation account of mindreading. Here, we question the motor theory of social cognition and give reasons for our skepticism.