Finger drawing by infant chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

We introduced a new technique to investigate the development of scribbling in very young infants. We tested three infant chimpanzees to compare the developmental processes of scribbling between humans and chimpanzees. While human infants start to scribble on paper at around the age of 18 months, our 13- to 23-month-old infant chimpanzees had never been observed scribbling prior to this study. We used a notebook computer with a touch-sensitive screen. This apparatus was able to record the location of the subjects touches on the screen. Each touch generated a fingertip-sized dot at the corresponding on-screen location. During spontaneous interactions with this apparatus, all three infants and two mother chimpanzees left scribbles with their fingers on the screen. The scribbles contained not only simple dots or short lines, but also curves and hook-like lines or loops, most of which were observed in the instrumental drawings of adult chimpanzees. The results suggest that perceptual-motor control for finger drawing develops in infant chimpanzees. Two of the infants performed their first scribble with a marker on paper at the age of 20–23 months. Just prior to this, they showed a rapid increase in combinatory manipulation of objects. These findings suggest that the development of combinatory manipulation of objects as well as that of perceptual-motor control may be necessary for the emergence of instrumental drawing on paper.     

Cognitive development in object manipulation by infant chimpanzees

This study focuses on the development of spontaneous object manipulation in three infant chimpanzees during their first 2 years of life. The three infants were raised by their biological mothers who lived among a group of chimpanzees. A human tester conducted a series of cognitive tests in a triadic situation where mothers collaborated with the researcher during the testing of the infants. Four tasks were presented, taken from normative studies of cognitive development of Japanese infants: inserting objects into corresponding holes in a box, seriating nesting cups, inserting variously shaped objects into corresponding holes in a template, and stacking up wooden blocks. The mothers had already acquired skills to perform these manipulation tasks. The infants were free to observe the mothers' manipulative behavior from immediately after birth. We focused on object–object combinations that were made spontaneously by the infant chimpanzees, without providing food reinforcement for any specific behavior that the infants performed. The three main findings can be summarized as follows. First, there was precocious appearance of object–object combination in infant chimpanzees: the age of onset (8–11 months) was comparable to that in humans (around 10 months old).Second, object–object combinations in chimpanzees remained at a low frequency between 11 and 16 months, then increased dramatically at the age of approximately 1.5 years. At the same time, the accuracy of these object–object combinations also increased. Third, chimpanzee infants showed inserting behavior frequently and from an early age but they did not exhibit stacking behavior during their first 2 years of life, in clear contrast to human data.     

Differential reliance of chimpanzees and humans on automatic and deliberate control of motor actions

Humans are often unaware of how they control their limb motor movements. People pay attention to their own motor movements only when their usual motor routines encounter errors. Yet little is known about the extent to which voluntary actions rely on automatic control and when automatic control shifts to deliberate control in nonhuman primates. In this study, we demonstrate that chimpanzees and humans showed similar limb motor adjustment in response to feedback error during reaching actions, whereas attentional allocation inferred from gaze behavior differed. We found that humans shifted attention to their own motor kinematics as errors were induced in motor trajectory feedback regardless of whether the errors actually disrupted their reaching their action goals. In contrast, chimpanzees shifted attention to motor execution only when errors actually interfered with their achieving a planned action goal. These results indicate that the species differed in their criteria for shifting from automatic to deliberate control of motor actions. It is widely accepted that sophisticated motor repertoires have evolved in humans. Our results suggest that the deliberate monitoring of one’s own motor kinematics may have evolved in the human lineage.     

Enculturated chimpanzees imitate rationally

Human infants imitate others' actions 'rationally': they copy a demonstrator's action when that action is freely chosen, but less when it is forced by some constraint (Gergely, Bekkering & Király, 2002). We investigated whether enculturated chimpanzees (Pan troglodytes) also imitate rationally. Using Gergely and colleagues' (2002) basic procedure, a human demonstrator operated each of six apparatuses using an unusual body part (he pressed it with his forehead or foot, or sat on it). In the Hands Free condition he used this unusual means even though his hands were free, suggesting a free choice. In the Hands Occupied condition he used the unusual means only because his hands were occupied, suggesting a constrained or forced choice. Like human infants, chimpanzees imitated the modeled action more often in the Hands Free than in the Hands Occupied condition. Enculturated chimpanzees thus have some understanding of the rationality of others' intentional actions, and use this understanding when imitating others.     

Development of manipulatory skills and the deployment of attention

Two independent tasks, object manipulation and auditory-visual matching, were used to examine the relationship between developing manual action skills and attention to intermodal object properties in 3.5- and 5.5-month-olds. Although handling skills improved with age, with older infants demonstrating more varied manipulation, there were no age differences for the matching task. When grouped by handling skills, a significant interaction between skill and event type was found for the two age groups combined and for 5.5-month-olds alone. Auditory-visual matching of social events did not vary with handling skills, whereas auditory-visualmatching of object events did. Infants at higher skill levels responded similarly to social and object events, whereas less skilled infants' matching preferences were weaker for object events. These findings indicate that infants increase their attention to auditory and visual properties of objects as this information becomes useful for guiding new actions. This effect is independent of age due to considerable individual variability in the development of object handling skills.     

The generalization of deferred imitation in enculturated chimpanzees (Pan troglodytes)

Deferred imitation of object-related actions and generalization of imitation to similar but not identical tasks was assessed in three human-reared (enculturated) chimpanzees, ranging in age from 5 to 9 years. Each ape displayed high levels of deferred imitation and only slightly lower levels of generalization of imitation. The youngest two chimpanzees were more apt to generalize the model's actions when they had displayed portions of the target behaviors at baseline, consistent with the idea that learning is more likely to occur when working within the "zone of proximal development." We argue that generalization of imitation is the best evidence to date of imitative learning in chimpanzees. Electronic Publication     

Goal saliency boosts infants’ action prediction for human manual actions,but not for mechanical claws

Previous research indicates that infants’ prediction of the goals of observed actions is influenced by own experience with the type of agent performing the action (i.e., human hand vs. non-human agent) as well as by action-relevant features of goal objects (e.g., object size). The present study investigated the combined effects of these factors on 12-month-olds’ action prediction. Infants’ (N = 49) goal-directed gaze shifts were recorded as they observed 14 trials in which either a human hand or a mechanical claw reached for a small goal area (low-saliency goal) or a large goal area (high-saliency goal). Only infants who had observed the human hand reaching for a high-saliency goal fixated the goal object ahead of time, and they rapidly learned to predict the action goal across trials. By contrast, infants in all other conditions did not track the observed action in a predictive manner, and their gaze shifts to the action goal did not change systematically across trials. Thus, high-saliency goals seem to boost infants’ predictive gaze shifts during the observation of human manual actions, but not of actions performed by a mechanical device. This supports the assumption that infants’ action predictions are based on interactive effects of action-relevant object features (e.g., size) and own action experience.     

Factors influencing imitation of manipulatory actions in chimpanzees (Pan troglodytes).

The purpose of the study was to investigate what kind of factors determine the degree of difficulty for chimpanzees (Pan troglodytes) when they imitate actions. Five adult chimpanzees were instructed to perform 48 arbitrary manipulatory actions consisting of different bodily motor patterns and object directionality. Results showed that actions in which an object is directed toward another external location (another object and one's own body) were easier to perform than those that involved manipulating a single object alone. Actions involving unfamiliar motor patterns were more difficult to perform than those involving familiar motor patterns that were already present in the subject's repertoire. Error responses were characterized as perseverative repetition of previously instructed actions. These findings suggest that chimpanzees find the directionality of manipulated objects a more salient cue than details of the demonstrator's body movements performing the manipulation.     

Extrapolation and direct matching mediate anticipation in infancy

Why are infants able to anticipate occlusion events and other people's actions but not the movement of self-propelled objects? This study investigated infant and adult anticipatory gaze shifts during observation of self-propelled objects and human goal-directed actions. Six-month-old infants anticipated self-propelled balls but not human actions. This demonstrates that different processes mediate the ability to anticipate human actions (direct matching) versus self-propelled objects (extrapolation).     

Human ostensive signals do not enhance gaze following in chimpanzees,but do enhance object-oriented attention

The previous studies have shown that human infants and domestic dogs follow the gaze of a human agent only when the agent has addressed them ostensively—e.g., by making eye contact, or calling their name. This evidence is interpreted as showing that they expect ostensive signals to precede referential information. The present study tested chimpanzees, one of the closest relatives to humans, in a series of eye-tracking experiments using an experimental design adapted from these previous studies. In the ostension conditions, a human actor made eye contact, called the participant’s name, and then looked at one of two objects. In the control conditions, a salient cue, which differed in each experiment (a colorful object, the actor’s nodding, or an eating action), attracted participants’ attention to the actor’s face, and then the actor looked at the object. Overall, chimpanzees followed the actor’s gaze to the cued object in both ostension and control conditions, and the ostensive signals did not enhance gaze following more than the control attention-getters. However, the ostensive signals enhanced subsequent attention to both target and distractor objects (but not to the actor’s face) more strongly than the control attention-getters—especially in the chimpanzees who had a close relationship with human caregivers. We interpret this as showing that chimpanzees have a simple form of communicative expectations on the basis of ostensive signals, but unlike human infants and dogs, they do not subsequently use the experimenter’s gaze to infer the intended referent. These results may reflect a limitation of non-domesticated species for interpreting humans’ ostensive signals in inter-species communication.     

Ontogeny of manipulative behavior and nut‐cracking in young tufted capuchin monkeys (Cebus apella): a Perception–action perspective

How do capuchin monkeys learn to use stones to crack open nuts? Perception–action theory posits that individuals explore producing varying spatial and force relations among objects and surfaces, thereby learning about affordances of such relations and how to produce them. Such learning supports the discovery of tool use. We present longitudinal developmental data from semifree‐ranging tufted capuchin monkeys (Cebus apella) to evaluate predictions arising from Perception–action theory linking manipulative development and the onset of tool‐using. Percussive actions bringing an object into contact with a surface appeared within the first year of life. Most infants readily struck nuts and other objects against stones or other surfaces from 6 months of age, but percussive actions alone were not sufficient to produce nut‐cracking sequences. Placing the nut on the anvil surface and then releasing it, so that it could be struck with a stone, was the last element necessary for nut‐cracking to appear in capuchins. Young chimpanzees may face a different challenge in learning to crack nuts: they readily place objects on surfaces and release them, but rarely vigorously strike objects against surfaces or other objects. Thus the challenges facing the two species in developing the same behavior (nut‐cracking using a stone hammer and an anvil) may be quite different. Capuchins must inhibit a strong bias to hold nuts so that they can release them; chimpanzees must generate a percussive action rather than a gentle placing action. Generating the right actions may be as challenging as achieving the right sequence of actions in both species. Our analysis suggests a new direction for studies of social influence on young primates learning sequences of actions involving manipulation of objects in relation to surfaces.     

Outcome-based observational learning in human infants

Previous work shows that infants manifest emulation learning in the use of end-state information. Outcome-based emulation has been interpreted as affordance learning or goal attribution. The present paper explores whether these two learning possibilities might be related. In 3 experiments, 17-month-old infants (N = 180) were presented with action outcomes across a variety of contexts and tasks: They observed either the full demonstration or the model's starting and final postures, plus the initial and end states of the object, or the latter portion of the foregoing display, or the end state of the object alone. The tasks included combinatory, noncombinatory, and body movement acts. Infants reproduced observed outcomes most often by observing the full demonstration. A similar effect was attained by exposure to both posture and configuration changes, but the effect was subject to the combinatory nature of the apparatus. In contrast, performance was less efficient after seeing the object's end state alone, suggesting that infants in the previous conditions did not simply emulate in association with the affordances. These findings support the notion that goal attribution based on sensitivity to bodily cues is reliant on the clarity of the affordances of a task.     

Spontaneous adaptation explains why people act faster when being imitated

The human ability to perform joint actions is often attributed to high-level cognitive processes. For example, the finding that action leaders act faster when imitated by their partners has been interpreted as evidence for anticipation of the other’s actions (Pfister, Dignath, Hommel, & Kunde, 2013). In two experiments, we showed that a low-level mechanism can account for this finding. Action leaders were faster when imitated than when counterimitated, but only if they could observe their partner’s actions (Exp. 1). Crucially, when due to our manipulation the partner’s imitative actions became slower than the counterimitative actions, leaders also became slower when they were imitated, and faster when counterimitated (Exp. 2). Our results suggest that spontaneous temporal adaptation is a key mechanism in joint action tasks. We argue for a reconsideration of other phenomena that have traditionally been attributed solely to high-level processes.     

Disposition to recognize goals in infant chimpanzees

Do nonhuman primates attribute goals to others? Traditional studies with chimpanzees provide equivocal evidence for “mind reading” in nonhuman primates. Here we adopt looking time, a methodology commonly used with human infants to test infant chimpanzees. In this experiment, four infant chimpanzees saw computer-generated stimuli that mimicked a goal-directed behavior. The baby chimps performed as well as human infants, namely, they were sensitive to the trajectories of the objects, thus suggesting that chimpanzees may be endowed with a disposition to understand goal-directed behaviors. The theoretical implications of these results are discussed.     

The link between infant attention to goal‐directed action and later theory of mind abilities

Various studies have shown that infants in their first year of life are able to interpret human actions as goal‐directed. It is argued that this understanding is a precondition for understanding intentional actions and attributing mental states. Moreover, some authors claim that this early action understanding is a precursor of later Theory of Mind (ToM) development. To test this, we related 6‐month‐olds’ performance in an action interpretation task to their performance in ToM tasks at the age of 4 years. Action understanding was assessed using a modified version of the Woodward‐paradigm ( Woodward, 1999 ). At the age of 4 years, the same children were tested with the German version of the ToM scale developed by Wellman and Liu (2004 ). Results revealed a correlation between infants’ decrement of attention to goal‐directed action and their ability to solve a false belief task at the age of 4 years with no modulation by language abilities. Our results indicate a link between infant attention to goal‐directed action and later theory of mind abilities.     

Social-cognitive skills between 5 and 10 months of age

Joint attention skills are an important part of human cultural learning. However, little is known about the emergence and meaning of these skills in early ontogeny. The development of, and relation among, various joint attention skills was assessed. Seventy-two 5 to 10-month-old infants were tested on a variety of joint attention tasks. Intercorrelations among these tasks were sparse, which puts into question the meaning of these various skills. In addition, the majority of infants exhibited some joint attention skill before 9 months of age, which points to a more gradual development of joint attention skills than suggested by previous research.     

Action production influences 12-month-old infants' attention to others' actions

Recent work implicates a link between action control systems and action understanding. In this study, we investigated the role of the motor system in the development of visual anticipation of others' actions. Twelve-month-olds engaged in behavioral and observation tasks. Containment activity, infants' spontaneous engagement in producing containment actions; and gaze latency, how quickly they shifted gaze to the goal object of another's containment actions, were measured. Findings revealed a positive relationship: infants who received the behavior task first evidenced a strong correlation between their own actions and their subsequent gaze latency of another's actions. Learning over the course of trials was not evident. These findings demonstrate a direct influence of the motor system on online visual attention to others' actions early in development.     

Goal attribution in chimpanzees

Does the chimpanzee attribute goals to others? Recent infant studies using the looking time measure have been interpreted as evidence that human infants attribute goals. An experiment modeled on these studies was carried out on chimpanzees, and the chimpanzees responded the way infants do. This indicates that chimpanzees also attribute goals and hence that this capacity is not distinctively human.     

Imitation of intentional manipulatory actions in chimpanzees (Pan troglodytes)

In this study, the authors investigated the understanding of other's actions in 5 adult chimpanzees (Pan troglodytes). A human demonstrated an attempt to open different containers. Each container required a different motor pattern to open it. Along with the container, a 2nd object was made available. After a free play period in which the chimpanzees' natural behaviors toward the objects were recorded, the authors tested the following 2 phases: The demonstrator (a) tried but failed to open and (b) opened the container successfully, with 1 of 2 alternative strategies, either using an "irrelevant tool" or by hand. The chimpanzees did not reproduce the demonstrator's motor patterns precisely but did reproduce the demonstrated strategies in both phases. These results suggest that chimpanzees anticipate the intentions of others by perceiving the directionality and causality of object(s) as available cues.     

When the rules are reversed: Action-monitoring consequences of reversing stimulus–response mappings

How does switching tasks affect our ability to monitor and adapt our behavior? Largely independent lines of research have examined how individuals monitor their actions and adjust to errors, on the one hand, and how they are able to switch between two or more tasks, on the other. Few studies, however, have explored how these two aspects of cognitive?Cbehavioral flexibility interact. That is, how individuals monitor their actions when task rules are switched remains unknown. The present study sought to address this question by examining the action-monitoring consequences of response switching??a form of task switching that involves switching the response that is associated with a particular stimulus. We recorded event-related brain potentials (ERPs) while participants performed a modified letter flanker task in which the stimulus?Cresponse (S?CR) mappings were reversed between blocks. Specifically, we examined three ERPs??the N2, the error-related negativity (ERN), and the error positivity (Pe)??that have been closely associated with action monitoring. The findings revealed that S?CR reversal blocks were associated with dynamic alterations of action-monitoring brain activity: the N2 and ERN were enhanced, whereas the Pe was reduced. Moreover, participants were less likely to adapt their posterror behavior in S?CR reversal blocks. Taken together, these data suggest that response switching results in early enhancements of effortful control mechanisms (N2 and ERN) at the expense of reductions in later response evaluation processes (Pe). Thus, when rules change, our attempts at control are accompanied by less attention to our actions.