Do infants provide evidence that the mirror system is involved in action understanding?

Do dogs preferentially encode the identity of the target object or the location of others' actions?

The ability to make sense of and predict others' actions is foundational for many socio-cognitive abilities. Dogs (Canis familiaris) constitute interesting comparative models for the study of action perception due to their marked sensitivity to human actions. We tested companion dogs (N = 21) in two screen-based eye-tracking experiments, adopting a task previously used with human infants and apes, to assess which aspects of an agent's action dogs consider relevant to the agent's underlying intentions. An agent was shown repeatedly acting upon the same one of two objects, positioned in the same location. We then presented the objects in swapped locations and the agent approached the objects centrally (Experiment 1) or the old object in the new location or the new object in the old location (Experiment 2). Dogs' anticipatory fixations and looking times did not reflect an expectation that agents should have continued approaching the same object nor the same location as witnessed during the brief familiarization phase; this contrasts with some findings with infants and apes, but aligns with findings in younger infants before they have sufficient motor experience with the observed action. However, dogs' pupil dilation and latency to make an anticipatory fixation suggested that, if anything, dogs expected the agents to keep approaching the same location rather than the same object, and their looking times showed sensitivity to the animacy of the agents. We conclude that dogs, lacking motor experience with the observed actions of grasping or kicking performed by a human or inanimate agent, might interpret such actions as directed toward a specific location rather than a specific object. Future research will need to further probe the suitability of anticipatory looking as measure of dogs' socio-cognitive abilities given differences between the visual systems of dogs and primates.

Dogs Rely On Visual Cues Rather Than On Effector-Specific Movement Representations to Predict Human Action Targets

The ability to predict others' actions is one of the main pillars of social cognition. We investigated the processes underlying this ability by pitting motor representations of the observed movements against visual familiarity. In two pre-registered eye-tracking experiments, we measured the gaze arrival times of 16 dogs (Canis familiaris) who observed videos of a human or a conspecific executing the same goal-directed actions. On the first trial, when the human agent performed human-typical movements outside dogs' specific motor repertoire, dogs' gaze arrived at the target object anticipatorily (i.e., before the human touched the target object). When the agent was a conspecific, dogs' gaze arrived to the target object reactively (i.e., upon or after touch). When the human agent performed unusual movements more closely related to the dogs' motor possibilities (e.g., crawling instead of walking), dogs' gaze arrival times were intermediate between the other two conditions. In a replication experiment, with slightly different stimuli, dogs' looks to the target object were neither significantly predictive nor reactive, irrespective of the agent. However, when including looks at the target object that were not preceded by looks to the agents, on average dogs looked anticipatorily and sooner at the human agent's action target than at the conspecific's. Looking times and pupil size analyses suggest that the dogs' attention was captured more by the dog agent. These results suggest that visual familiarity with the observed action and saliency of the agent had a stronger influence on the dogs' looking behaviour than effector-specific movement representations in anticipating action targets.

The Impact of Action Effects on Infants' Predictive Gaze Shifts for a Non-Human Grasping Action at 7, 11, and 18 Months

During the observation of goal-directed actions, infants usually predict the goal at an earlier age when the agent is familiar (e.g., human hand) compared to unfamiliar (e.g., mechanical claw). These findings implicate a crucial role of the developing agentive self for infants’ processing of others’ action goals. Recent theoretical accounts suggest that predictive gaze behavior relies on an interplay between infants’ agentive experience (top-down processes) and perceptual information about the agent and the action-event (bottom-up information; e.g., agency cues). The present study examined 7-, 11-, and 18-month-old infants’ predictive gaze behavior for a grasping action performed by an unfamiliar tool, depending on infants’ age-related action knowledge about tool-use and the display of the agency cue of producing a salient action effect. The results are in line with the notion of a systematic interplay between experience-based top-down processes and cue-based bottom-up information: Regardless of the salient action effect, predictive gaze shifts did not occur in the 7-month-olds (least experienced age group), but did occur in the 18-month-olds (most experienced age group). In the 11-month-olds, however, predictive gaze shifts occurred only when a salient action effect was presented. This sheds new light on how the developing agentive self, in interplay with available agency cues, supports infants’ action-goal prediction also for observed tool-use actions.

Proactive gaze is present during biological and non-biological motion observation

Others' action observation activates in the observer a coordinated hand-eye motor program, covert for the hand (i.e. motor resonance), and overt for the eye (i.e. proactive gaze), similar to that of the observed agent. The biological motion hypothesis of action anticipation claims that proactive gaze occurs only in the presence of biological motion, and that kinematic information is sufficient to determine the anticipation process. The results of the present study did not support the biological motion hypothesis of action anticipation. Specifically, proactive gaze was present during observation of both a biological accelerated-decelerated motion and a non-biological constant velocity motion (Experiment 1), in the presence of a barrier able to restrict differences between the two kinematics to the motion profile of individual markers prior to contact (Experiment 2), but only if an object was present at the end point of the movement trajectory (Experiment 3). Furthermore, proactive gaze was found independently of the presence of end effects temporally congruent with the instant in which the movement stopped (Experiments 4, and 5). We propose that the involvement of the observer's motor system is not restricted to when the agent moves with natural kinematics, and it is mandatory whenever the presence of an agent or a goal is evident, regardless of physical appearance, natural kinematics, and the possibility to identify the action behind the stimulus.

The impact of salient action effects on 6-, 7-, and 11-month-olds' goal-predictive gaze shifts for a human grasping action

When infants observe a human grasping action, experience-based accounts predict that all infants familiar with grasping actions should be able to predict the goal regardless of additional agency cues such as an action effect. Cue-based accounts, however, suggest that infants use agency cues to identify and predict action goals when the action or the agent is not familiar. From these accounts, we hypothesized that younger infants would need additional agency cues such as a salient action effect to predict the goal of a human grasping action, whereas older infants should be able to predict the goal regardless of agency cues. In three experiments, we presented 6-, 7-, and 11-month-olds with videos of a manual grasping action presented either with or without an additional salient action effect (Exp. 1 and 2), or we presented 7-month-olds with videos of a mechanical claw performing a grasping action presented with a salient action effect (Exp. 3). The 6-month-olds showed tracking gaze behavior, and the 11-month-olds showed predictive gaze behavior, regardless of the action effect. However, the 7-month-olds showed predictive gaze behavior in the action-effect condition, but tracking gaze behavior in the no-action-effect condition and in the action-effect condition with a mechanical claw. The results therefore support the idea that salient action effects are especially important for infants' goal predictions from 7 months on, and that this facilitating influence of action effects is selective for the observation of human hands.

Altercentric Cognition: How Others Influence Our Cognitive Processing

Humans are ultrasocial, yet, theories of cognition have often been occupied with the solitary mind. Over the past decade, an increasing volume of work has revealed how individual cognition is influenced by the presence of others. Not only do we rapidly identify others in our environment, but we also align our attention with their attention, which influences what we perceive, represent, and remember, even when our immediate goals do not involve coordination. Here, we refer to the human sensitivity to others and to the targets and content of their attention as 'altercentrism'; and aim to bring seemingly disparate findings together, suggesting that they are all reflections of the altercentric nature of human cognition.

The role of the motor system in action understanding and communication: Evidence from human infants and non-human primates

There is growing evidence that activation of the motor system during observation of actions, a phenomenon first observed in non-human primates, underlies action understanding and even communication. This review (a) examines the evidence on motor system activity as an underlying neural correlate of action understanding; (b) reviews the theoretical and empirical work linking action understanding and the development of communication, with a specific focus on the role that gestures play as an intermediary; and (c) discusses the research on and existing opportunities for understanding the link between the motor system and communication in both humans and non-human primates, through the lens of action perception. Bringing together findings and perspectives from developmental social cognition in both humans and non-human primates and applying recent neuroscientific perspectives will help to elucidate the processes underlying the ability to understand and communicate with others.

Typical predictive eye movements during action observation without effector-specific motor simulation

When watching someone reaching to grasp an object, we typically gaze at the object before the agent's hand reaches it-that is, we make a "predictive eye movement" to the object. The received explanation is that predictive eye movements rely on a direct matching process, by which the observed action is mapped onto the motor representation of the same body movements in the observer's brain. In this article, we report evidence that calls for a reexamination of this account. We recorded the eye movements of an individual born without arms (D.C.) while he watched an actor reaching for one of two different-sized objects with a power grasp, a precision grasp, or a closed fist. D.C. showed typical predictive eye movements modulated by the actor's hand shape. This finding constitutes proof of concept that predictive eye movements during action observation can rely on visual and inferential processes, unaided by effector-specific motor simulation.

Reaching the goal: Active experience facilitates 8-month-old infants' prospective analysis of goal-based actions

From early in development, infants view others' actions as structured by intentions, and this action knowledge may be supported by shared action production/perception systems. Because the motor system is inherently prospective, infants' understanding of goal-directed actions should support predictions of others' future actions, yet little is known about the nature and developmental origins of this ability, specifically whether young infants use the goal-directed nature of an action to rapidly predict future social behaviors and whether their action experience influences this ability. Across three conditions, we varied the level of action experience infants engaged in to determine whether motor priming influenced infants' ability to generate rapid social predictions. Results revealed that young infants accurately generated goal-based visual predictions when they had previously been reaching for objects; however, infants who passively observed a demonstration were less successful. Further analyses showed that engaging the cognitively based prediction system to generate goal-based predictions following motor engagement resulted in slower latencies to predict, suggesting that these smart predictions take more time to deploy. Thus, 8-month-old infants may have motor representations of goal-directed actions, yet this is not sufficient for them to predict others' actions; rather, their own action experience supports the ability to rapidly implement knowledge to predict future behavior.

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.

Infants' Understanding of Object-Directed Action: An Interdisciplinary Synthesis

Recognizing that the object-directed actions of others are governed by goals and intentions is a crucial component of human interaction. These actions often occur rapidly and without explanation, yet we learn from and predict the actions of others with remarkable speed and accuracy, even during the first year of life. This review paper will serve as a bridge between several disparate literatures that, we suggest, can each contribute to our understanding of how infants interpret action. Specifically, we provide a review not just of research on infant goal attribution per se, but also incorporate findings from studies on the mirror neuron system and infant object cognition. The integration of these various research approaches allows for a novel construal of the extents and limits of early goal attribution – one in which the importance of the entire action context is considered – and points to specific future research directions.

Typical action perception and interpretation without motor simulation

Every day, we interact with people synchronously, immediately understand what they are doing, and easily infer their mental state and the likely outcome of their actions from their kinematics. According to various motor simulation theories of perception, such efficient perceptual processing of others' actions cannot be achieved by visual analysis of the movements alone but requires a process of motor simulation--an unconscious, covert imitation of the observed movements. According to this hypothesis, individuals incapable of simulating observed movements in their motor system should have difficulty perceiving and interpreting observed actions. Contrary to this prediction, we found across eight sensitive experiments that individuals born with absent or severely shortened upper limbs (upper limb dysplasia), despite some variability, could perceive, anticipate, predict, comprehend, and memorize upper limb actions, which they cannot simulate, as efficiently as typically developed participants. We also found that, like the typically developed participants, the dysplasic participants systematically perceived the position of moving upper limbs slightly ahead of their real position but only when the anticipated position was not biomechanically awkward. Such anticipatory bias and its modulation by implicit knowledge of the body biomechanical constraints were previously considered as indexes of the crucial role of motor simulation in action perception. Our findings undermine this assumption and the theories that place the locus of action perception and comprehension in the motor system and invite a shift in the focus of future research to the question of how the visuo-perceptual system represents and processes observed body movements and actions.

Eye Movements During Action Observation

An important element in social interactions is predicting the goals of others, including the goals of others' manual actions. Over a decade ago, Flanagan and Johansson demonstrated that, when observing other people reaching for objects, the observer's gaze arrives at the goal before the action is completed. Moreover, those authors proposed that this behavior was mediated by an embodied process, which takes advantage of the observer's motor knowledge. Here, we scrutinize work that has followed that seminal article. We include studies on adults that have used combined eye tracking and transcranial magnetic stimulation technologies to test causal hypotheses about underlying brain circuits. We also include developmental studies on human infants. We conclude that, although several aspects of the embodied process of predictive eye movements remain to be clarified, current evidence strongly suggests that the motor system plays a causal role in guiding predictive gaze shifts that focus on another person's future goal. The early emergence of the predictive gaze in infant development underlines its importance for social cognition and interaction.

Engagement: Looking beyond the mirror to understand action understanding

In this paper, we argue that the current focus on mirroring as the route to explaining the development of action understanding is misleading and problematic. It facilitates a fundamentally spectatorial stance, ignoring engagement and dialogue; it focuses on similarity between self and other and neglects difference; and it succumbs to the static terminology of mechanism rather than a dynamic language of process. Contrary to this view, dialogic exchanges are evident from the start of life, revealing infants' ability to engage with and respond appropriately to actions that are outside their own motor repertoire. We suggest that engagement rather than mirroring better accounts for many current findings in action understanding. The neurological evidence to date shows that action perception involves a process of continuous synchronization and change, suggesting that it might be more fruitful for research and theory to look beyond mirroring and instead adopt dynamic processual explanations of action understanding within interaction.

Short-term Motor Training, but Not Observational Training, Alters Neurocognitive Mechanisms of Action Processing in Infancy

The role of motor experience in the processing of perceived actions is hotly debated on both behavioral (e.g., action understanding) and neural (e.g., activation of the motor system) levels of interpretation. Whereas some researchers focus on the role of motor experience in the understanding of and motor activity associated with perceived actions, others emphasize the role of visual experience with the perceived actions. The question of whether prior firsthand motor experience is critical to motor system activation during perception of actions performed by others is best addressed through studies with infants who have a limited repertoire of motor actions. In this way, infants can receive motor or visual training with novel actions that are not mere recombinations of previously acquired actions. In this study, 10-month-old infants received active training with a motorically unfamiliar action that resulted in a distinct sound effect. They received observational experience with a second, similarly unfamiliar action. Following training, we assessed infants' neural motor activity via EEG while they listened to the sounds associated with the actions relative to a novel sound. We found a greater decrease in mu power to sounds associated with the motorically learned action than to those associated with the observed action that the infants had never produced. This effect was directly related to individual differences in the degree of motor learning via motor training. These findings indicate a unique effect of active experience on neural correlates of action perception.

Brain representation of action observation in human infants

Imitative learning has long been established as extremely important for early development. However, neural mechanisms involved in early imitative behaviours are still areas of active research. Neurophysiological and brain-imaging studies have been recently performed that provide initial evidence of brain activation associated with action observation in the first months of life. In this review we examine all studies exploring the effects of action observation on brain function assessed by means of non-invasive brain-mapping techniques. Seventeen papers were selected as a result of our literature search. The strongest evidence for a neural signature of action observation comes from studies exploring the desynchronization of the μ-rhythm, which was reported for both occluded and visible goal-directed grasp, and was correlated with the totality of the infant's own action experience. The effects of action observation were reported on event-related potentials (ERPs) or near infrared spectroscopy. Taken together, these studies suggest that, in early infancy, a direct visual-motor matching process is already detectable as early as 6 months, suggesting a matching between action perception and execution already in infancy. If confirmed by future studies, these findings will shed light on the mechanisms of early motor development and imitation, and will be key to informing novel rehabilitation strategies in infants with congenital brain damage.

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.

Action-based effects on music perception

The classical, disembodied approach to music cognition conceptualizes action and perception as separate, peripheral processes. In contrast, embodied accounts of music cognition emphasize the central role of the close coupling of action and perception. It is a commonly established fact that perception spurs action tendencies. We present a theoretical framework that captures the ways in which the human motor system and its actions can reciprocally influence the perception of music. The cornerstone of this framework is the common coding theory, postulating a representational overlap in the brain between the planning, the execution, and the perception of movement. The integration of action and perception in so-called internal models is explained as a result of associative learning processes. Characteristic of internal models is that they allow intended or perceived sensory states to be transferred into corresponding motor commands (inverse modeling), and vice versa, to predict the sensory outcomes of planned actions (forward modeling). Embodied accounts typically refer to inverse modeling to explain action effects on music perception (Leman, 2007). We extend this account by pinpointing forward modeling as an alternative mechanism by which action can modulate perception. We provide an extensive overview of recent empirical evidence in support of this idea. Additionally, we demonstrate that motor dysfunctions can cause perceptual disabilities, supporting the main idea of the paper that the human motor system plays a functional role in auditory perception. The finding that music perception is shaped by the human motor system and its actions suggests that the musical mind is highly embodied. However, we advocate for a more radical approach to embodied (music) cognition in the sense that it needs to be considered as a dynamical process, in which aspects of action, perception, introspection, and social interaction are of crucial importance.