Infants’ understanding of actions performed by mechanical devices

Adaptive rule learning of event sequences during the A-not-B task in 9-month-old infants

Prior work indicates that infants can use social information to organize simple audiovisual inputs into predictable rules by 8 months of age. However, it is unclear whether infants can use social information to organize more complex events into predictable rules that can be used to guide motor action. To examine these issues, we tested 9-month-old infants using a modified version of an A-not-B task, in which hiding event sequences were paired with different experimenters, who could be used to organize the events into rules that guide action. We predicted that infants' reaching accuracy would be better when the experimenter changes when the toy's hiding location changes, relative to when the experimenter stays the same, as this should cue a novel rule used to guide action. Experiments 1 and 2 validated this prediction. Experiment 3 showed that reaching accuracy was better when the toy's hiding location switched but was consistent with the rule associated with the experimenter, relative to when the toy's hiding location repeated but was inconsistent with the rule associated with the experimenter. These data suggest that infants can use the identities of experimenters to organize events into predictable rules that guide action in the A-not-B task.

Investigating the social environment of the A-not-B search task

Controversy exists concerning the origins of object permanence, with different measures suggesting different conclusions. Looking measures have been interpreted as evidence for early understanding (Baillargeon, 1987, Developmental Psychology, 23:655), while Piaget (The construction of reality in the child, 1954) interpreted perseverative reaching behaviour on his AB search task to be indicative of limited understanding. However, looking measures are often reported to be an unreliable index of infant expectation (Haith, 1998, Infant Behaviour and Development, 21:167) and reaching behaviour has been explained by many alternative processes (e.g. Smith et al., 1999, Psychological Review, 106:235; Topál et al., 2008, Science, 321:1831). We aimed to investigate whether social looking (Dunn & Bremner, 2017, Developmental Science, 20:e12452; Walden et al., 2007, Developmental Science, 10:654) can be used as a valid measure of infant expectation of object location during the Piagetian AB search task. Furthermore, we aimed to test the social accounts of perseverative reaching by investigating how the direction of experimenter gaze would affect infant search and social behaviour. Infant search and social behaviour was compared on B trials across three different conditions, namely experimenter gaze to midline, location A and location B. Search performance significantly improved when the experimenter looked to location B. Infant social looking indicated that infants expect the object to be found in the location in which they search and are actively seeking information about object location from the experimenter. We conclude that social looking is a valid index of infant expectation that has provided support for the importance of the social environment on the AB search task. This casts doubt on the potential for this task to provide information related to the development of object permanence in infancy.

Death among primates: a critical review of non-human primate interactions towards their dead and dying

For the past two centuries, non-human primates have been reported to inspect, protect, retrieve, carry or drag the dead bodies of their conspecifics and, for nearly the same amount of time, sparse scientific attention has been paid to such behaviours. Given that there exists a considerable gap in the fossil and archaeological record concerning how early hominins might have interacted with their dead, extant primates may provide valuable insight into how and in which contexts thanatological behaviours would have occurred. First, we outline a comprehensive history of comparative thanatology in non-human primates, from the earliest accounts to the present, uncovering the interpretations of previous researchers and their contributions to the field of primate thanatology. Many of the typical behavioural patterns towards the dead seen in the past are consistent with those observed today. Second, we review recent evidence of thanatological responses and organise it into distinct terminologies: direct interactions (physical contact with the corpse) and secondary interactions (guarding the corpse, vigils and visitations). Third, we provide a critical evaluation regarding the form and function of the behavioural and emotional aspects of these responses towards infants and adults, also comparing them with non-conspecifics. We suggest that thanatological interactions: promote a faster re-categorisation from living to dead, decrease costly vigilant/caregiving behaviours, are crucial to the management of grieving responses, update position in the group's hierarchy, and accelerate the formation of new social bonds. Fourth, we propose an integrated model of Life-Death Awareness, whereupon neural circuitry dedicated towards detecting life, i.e. the agency system (animate agency, intentional agency, mentalistic agency) works with a corresponding system that interacts with it on a decision-making level (animate/inanimate distinction, living/dead discrimination, death awareness). Theoretically, both systems are governed by specific cognitive mechanisms (perceptual categories, associative concepts and high-order reasoning, respectively). Fifth, we present an evolutionary timeline from rudimentary thanatological responses likely occurring in earlier non-human primates during the Eocene to the more elaborate mortuary practices attributed to genus Homo throughout the Pleistocene. Finally, we discuss the importance of detailed reports on primate thanatology and propose several empirical avenues to shed further light on this topic. This review expands and builds upon previous attempts to evaluate the body of knowledge on this subject, providing an integrative perspective and bringing together different fields of research to detail the evolutionary, sensory/cognitive, developmental and historical/archaeological aspects of primate thanatology. Considering all these findings and given their cognitive abilities, we argue that non-human primates are capable of an implicit awareness of death.

Does watching Han Solo or C-3PO similarly influence our language processing?

Several studies have demonstrated that perceiving an action influences the subsequent processing of action verbs. However, which characteristics of the perceived action are truly determinant to enable this influence is still unknown. The current study investigated the role of the agent executing an action in this action-language relationship. Participants performed a semantic decision task after seeing a video of a human or a robot performing an action. The results of the first study showed that perceiving a human being executing an action as well as perceiving a robot facilitate subsequent language processing, suggesting that the humanness (The term "humanness" is used as meaning "belonging to human race" and not to refer to a personal quality) of the agent is not crucial in the link between action and language. However, this experiment was conducted with Japanese people who are very familiar with robots; thus, an alternative explanation could be that it is the unfamiliarity with the agent that could perturb the action-language relationship. To assess this hypothesis, we carried out two additional experiments with French participants. The results of the second study showed that, unlike the observation of a human agent, the observation of a robot did not influence language processing. Finally, the results of the third study showed that, after a familiarization phase, French participants too were influenced by the observation of a robot. Overall, the outcomes of these studies indicate that, more than the humanness of the agent, it is the familiarity which we have with this agent that is crucial in the action-language relationship.

Individual differences in object-processing explain the relationship between early gaze-following and later language development

Gaze-following behaviors play an important role in language development. However, the way in which gaze-following contributes to language development remains unclear. By focusing on two abilities, namely following the gaze direction of others and processing a cued object, the present study investigated how these two influences work together to promote language development in a longitudinal approach on infants from 9 to 18months of age. The results demonstrated that infants who spent more time following the gaze direction toward an object were more efficient in processing the cued object at 9months and had larger vocabularies by 18months. Mediation analyses showed that the relationship between early gaze-following behavior and subsequent vocabulary size was explained by object-processing ability. Importantly, mere extended fixations on a target object without the initiation of another's gaze shift were not related to enhanced object-processing. Our findings suggest that following another's gaze shift toward the object has an impact on object-processing that could contribute to vocabulary development, elucidating a critical step in the path from early gaze-following ability to later language development.

Infants' motor simulation of observed actions is modulated by the visibility of the actor's body

Previous research suggests that 9-month-old infants will develop a response bias in the A-not-B search paradigm after only observing an experimenter search for a hidden object on A-trials. In the current experiment, we tested whether infants would persist in making errors when only the hands-and-arms of the experimenter were visible. Three different conditions were included: (1) the experimenter was silent while hiding and finding the object, (2) the experimenter communicated with the infant via infant-directed speech, or (3) the body of the experimenter was visible during the training phase before his head and body were occluded during the test phase. Unlike previous studies, the results revealed that a significant proportion of infants searched correctly when the body of the experimenter was not visible, and only the combination of infant-directed speech and familiarization with a fully-specified body resulted in a majority of infants committing search errors. These results are interpreted as suggesting that the likelihood of infants committing search errors is dependent on their motor simulation of the experimenter's reaching. The strength of this simulation is graded by the similarity between the observed action and the motor representation.

On the other hand: Increased cortical activation to human versus mechanical hands in infants

There is a large body of work demonstrating that infants are sensitive to the distinction between human and mechanical entities from the early months of life, and have different expectations for the way these entities move and interact. The current work investigates the extent to which the functional organization of the immature brain reflects these early emerging sensitivities. Infants aged 8months watched two kinds of hands (human or mechanical) engage in two kinds of events (one with a functional outcome and one without). Using functional near-infrared spectroscopy (fNIRS), we assessed hemodynamic activation in the left and right temporal and temporal-occipital cortex in response to these events. The neuroimaging data revealed a significantly greater increase in activation in the right middle-posterior temporal cortex to events executed by the human than the mechanical hand; the event in which the hand engaged (function or non-function) did not significantly influence hemodynamic responses. In comparison, the left middle-temporal cortex showed significantly greater activation to events executed by the human than mechanical hand, but only when the events were functionally relevant. That is, the left middle-posterior temporal cortex responded selectively to human (as compared to mechanical) agents, but only in the context of functionally relevant actions on objects. These results reveal that the immature brain is functionally specialized to support infants' processing of human and non-human agents as distinct entities. These results also shed light on the cognitive and cortical mechanisms that guide infants' learning about agentive action and object function.

Action perception in infancy: the plasticity of 7-month-olds' attention to grasping actions

The present study investigates the plasticity of 7-month-old infants' orienting of attention during their perception of grasping actions. Previous research has shown that when infants observe a grasping hand, they shift their attention in line with the grasping direction, which is indicated by a reliable priming effect in this direction. The mechanisms behind this priming effect are largely unknown, and it is unclear how malleable this priming effect is with respect to a brief exposure to novel action-target contingencies. In a spatial-cueing paradigm, we presented a series of training trials prior to a series of test trials. These training sequences significantly modulated infants' attention. This suggests that action perception, when assessed through shifts of attention, is not solely based on the infants' grasping experience but quickly adapts to context-specific observed regularities.

Infants' observation of others' actions: Brief movement-specific visual experience primes motor representations

Recent research suggests that infants' observation of others' reaching actions activates corresponding motor representations which develop with their motor experience. Contralateral reaching develops a few months later than ipsilateral reaching, and 9-month-old infants are less likely to map the observation of these reaches to their motor representations. The goal of the current study was to test whether a brief familiarization with contralateral reaching is sufficient to prime this less developed motor representation to increase the likelihood of its activation. In Experiment 1, infants were familiarized with contralateral reaching before they were tested in an observational version of the A-not-B paradigm. A significant number of infants searched incorrectly, suggesting that the observation of contralateral reaching primed their motor representations. In Experiment 2, infants were familiarized with ipsilateral reaching, which shared the goals but not the movements associated with the contralateral reaches observed during testing, and they did not show a search bias. Taken together, these results suggest that a brief familiarization with a movement-specific behaviour facilitates the direct matching of observed and executed actions.

Infants' online perception of give-and-take interactions

This research investigated infants' online perception of give-me gestures during observation of a social interaction. In the first experiment, goal-directed eye movements of 12-month-olds were recorded as they observed a give-and-take interaction in which an object is passed from one individual to another. Infants' gaze shifts from the passing hand to the receiving hand were significantly faster when the receiving hand formed a give-me gesture relative to when it was presented as an inverted hand shape. Experiment 2 revealed that infants' goal-directed gaze shifts were not based on different affordances of the two receiving hands. Two additional control experiments further demonstrated that differences in infants' online gaze behavior were not mediated by an attentional preference for the give-me gesture. Together, our findings provide evidence that properties of social action goals influence infants' online gaze during action observation. The current studies demonstrate that infants have expectations about well-formed object transfer actions between social agents. We suggest that 12-month-olds are sensitive to social goals within the context of give-and-take interactions while observing from a third-party perspective.

Motion, identity and the bias toward agency

The well-documented human bias toward agency as a cause and therefore an explanation of observed events is typically attributed to evolutionary selection for a "social brain". Based on a review of developmental and adult behavioral and neurocognitive data, it is argued that the bias toward agency is a result of the default human solution, developed during infancy, to the computational requirements of object re-identification over gaps in observation of more than a few seconds. If this model is correct, overriding the bias toward agency to construct mechanistic explanations of observed events requires structure-mapping inferences, implemented by the pre-motor action planning system, that replace agents with mechanisms as causes of unobserved changes in contextual or featural properties of objects. Experiments that would test this model are discussed.

The insufficiency of associative learning for explaining development: Three challenges to the associative account

Three challenges to the sufficiency of the associative account for explaining the development of mirror mechanisms are discussed: Genetic predispositions interact with associative learning, infants show predispositions to imitate human as opposed to nonhuman actions, and early and later learning involve different mechanisms. Legitimate objections to an extreme nativist account are raised, but the proposed solution is equally problematic.

Neurocognitive mechanisms underlying social learning in infancy: infants' neural processing of the effects of others' actions

Social transmission of knowledge is one of the reasons for human evolutionary success, and it has been suggested that already human infants possess eminent social learning abilities. However, nothing is known about the neurocognitive mechanisms that subserve infants' acquisition of novel action knowledge through the observation of other people's actions and their consequences in the physical world. In an electroencephalogram study on social learning in infancy, we demonstrate that 9-month-old infants represent the environmental effects of others' actions in their own motor system, although they never achieved these effects themselves before. The results provide first insights into the neurocognitive basis of human infants' unique ability for social learning of novel action knowledge.

The power of human gaze on infant learning

Social learning enables infants to acquire information, especially through communication. However, it is unknown whether humans are the prime source of information for infant learning. Here we report that humans have a powerful influence on infants' object learning compared with nonhuman agents (robots). Twelve-month-old infants were shown videos in which a human or a robot gazed at an object. The results demonstrated that the infants followed the gaze direction of both agents, but only human gaze facilitated their object learning: Infants showed enhanced processing of, and preferences for, the target object gazed at by the human but not by the robot. Importantly, an extended fixation on a target object without the orientation of human gaze did not produce these effects. Together, these findings show the importance of humanness in the gazer, suggesting that infants may be predisposed to treat humans as privileged sources of information for learning.

Infants understand the referential nature of human gaze but not robot gaze

Infants can acquire much information by following the gaze direction of others. This type of social learning is underpinned by the ability to understand the relationship between gaze direction and a referent object (i.e., the referential nature of gaze). However, it is unknown whether human gaze is a privileged cue for information that infants use. Comparing human gaze with nonhuman (robot) gaze, we investigated whether infants' understanding of the referential nature of looking is restricted to human gaze. In the current study, we developed a novel task that measured by eye-tracking infants' anticipation of an object from observing an agent's gaze shift. Results revealed that although 10- and 12-month-olds followed the gaze direction of both a human and a robot, only 12-month-olds predicted the appearance of objects from referential gaze information when the agent was the human. Such a prediction for objects reflects an understanding of referential gaze. Our study demonstrates that by 12 months of age, infants hold referential expectations specifically from the gaze shift of humans. These specific expectations from human gaze may enable infants to acquire various information that others convey in social learning and social interaction.