Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> When we observe someone performing an action, do our brains simulate making that action? Acquired motor skills offer a unique way to test this question, since people differ widely in the actions they have learned to perform. We used functional magnetic resonance imaging to study differences in brain activity between watching an action that one has learned to do and an action that one has not, in order to assess whether the brain processes of action observation are modulated by the expertise and motor repertoire of the observer. Experts in classical ballet, experts in capoeira and inexpertcontrolsubjectsviewedvideosofballetorcapoeiraactions. Comparingthebrainactivitywhendancerswatchedtheirowndance style versus the other style therefore reveals the influence of motor expertise on action observation. We found greater bilateral activations in premotor cortex and intraparietal sulcus, right superior parietal lobe and left posterior superior temporal sulcus when expert dancers viewed movements that they had been trained to perform compared to movements they had not. Our results show that this ‘mirror system’ integrates observed actions of others with an individual’s personal motor repertoire, and suggest that the human brain understands actions by motor simulation. <s> BIB001 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Is it possible to understand the intentions of other people by simply observing their actions? Many believe that this ability is made possible by the brain’s mirror neuron system through its direct link between action and observation. However, precisely how intentions can be inferred through action observation has provoked much debate. Here we suggest that the function of the mirror system can be understood within a predictive coding framework that appeals to the statistical approach known as empirical Bayes. Within this scheme the most likely cause of an observed action can be inferred by minimizing the prediction error at all levels of the cortical hierarchy that are engaged during action observation. This account identifies a precise role for the mirror system in our ability to infer intentions from actions and provides the outline of the underlying computational mechanisms. <s> BIB002 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Abstract The aim of the present study is to elucidate the influence of context on the kinematics of the reach-to-grasp movement. In particular, we consider two basic modes of social cognition, namely cooperation and competition. In two experiments kinematics of the very same action – reaching-to-grasp a wooden block – were analyzed in two different contexts provided by a cooperative task and competitive task. For the ‘cooperation’ tasks two participants were required to reach and grasp their respective objects and to cooperate to join the two objects in specific configurations in the middle of the working surface. For the ‘competition’ tasks, the two participants had to compete to place their own object first in the middle of the working surface. Results revealed specific kinematic patterns for cooperation and competition which were distinct from similar actions performed by each participant in isolation. Further, during the cooperation tasks, a high level of correlation between key kinematical parameters of the two participants was found. In accordance with evidence from neuroimaging, developmental and social psychology our results suggest the existence of motor patterns which reflect the intention to act in a social context. <s> BIB003 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Using a combination of behavioral measures and transcranial magnetic stimulation (TMS), this study finds that elite basketball players are better at predicting whether a free basketball throw will land in the basket or out and that they also have higher TMS-evoked motor potentials for when the ball misses its mark. <s> BIB004 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Body movement provides a rich source of information about other people’s goals and intentions. In the present study, we examined a particular aspect concerned with the interpretation of bodily movement—how well people can distinguish between different social intentions by observing a reach-to-grasp movement. To ascertain to what extent intention-from-motion judgements rely on visual kinematics, we compared prediction performance on a typical temporal-occlusion video task with prediction performance on a temporal-occlusion point-light task. In the video task, participants observed videos showing a model reaching towards and grasping a wooden block with different intents: to cooperate with a partner in building a tower, compete with an opponent to be the first to put the object in the middle of the working surface, or perform an individual action. In the point-light task, participants observed point-light displays of the same movements. Although predictions were more accurate for the video task, prediction performance was not disrupted for the point-light task, suggesting that essential kinematic information available in point-light displays was indeed sufficient for intention-from-motion judgement. Importantly, the same kinematic landmarks were used to discriminate between social intentions for the video and the point-light task. This suggests that observers not only have the ability to use kinematic information when no other information is available, but they use kinematic information to discriminate between intentions when watching the motion of others under full light conditions. <s> BIB005 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Explaining or predicting the behaviour of our conspecifics requires the ability to infer the intentions that motivate it. Such inferences are assumed to rely on two types of information: (1) the sensory information conveyed by movement kinematics and (2) the observer's prior expectations – acquired from past experience or derived from prior knowledge. However, the respective contribution of these two sources of information is still controversial. This controversy stems in part from the fact that “intention” is an umbrella term that may embrace various sub-types each being assigned different scopes and targets. We hypothesized that variations in the scope and target of intentions may account for variations in the contribution of visual kinematics and prior knowledge to the intention inference process. To test this hypothesis, we conducted four behavioural experiments in which participants were instructed to identify different types of intention: basic intentions (i.e. simple goal of a motor act), superordinate intentions (i.e. general goal of a sequence of motor acts), or social intentions (i.e. intentions accomplished in a context of reciprocal interaction). For each of the above-mentioned intentions, we varied (1) the amount of visual information available from the action scene and (2) participant's prior expectations concerning the intention that was more likely to be accomplished. First, we showed that intentional judgments depend on a consistent interaction between visual information and participant's prior expectations. Moreover, we demonstrated that this interaction varied according to the type of intention to be inferred, with participant's priors rather than perceptual evidence exerting a greater effect on the inference of social and superordinate intentions. The results are discussed by appealing to the specific properties of each type of intention considered and further interpreted in the light of a hierarchical model of action representation. <s> BIB006 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> This eye tracking study investigated the degree to which biological motion information from manual point-light displays provides sufficient information to elicit anticipatory eye movements. We compared gaze performance of adults observing a biological motion point-light display of a hand reaching for a goal object or a non-biological version of the same event. Participants anticipated the goal of the point-light action in the biological motion condition but not in a non-biological control condition. The present study demonstrates that kinematic information from biological motion can be used to anticipate the goal of other people’s point-light actions and that the presence of biological motion is sufficient for anticipation to occur. <s> BIB007 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> Abstract We examined the hypothesis that predictive gaze during observation of other people's actions depends on the activation of corresponding action plans in the observer. Using transcranial magnetic stimulation and eye-tracking technology we found that stimulation of the motor hand area, but not of the leg area, slowed gaze predictive behavior (compared to no TMS). This result shows that predictive eye movements to others' action goals depend on a somatotopical recruitment of the observer's motor system. The study provides direct support for the view that a direct matching process implemented in the mirror-neuron system plays a functional role for real-time goal prediction. <s> BIB008 </s> Predictive Mechanisms Are Not Involved the Same Way during Human-Human vs. Human-Machine Interactions: A Review <s> Passive Observation of Other Humans <s> In recent years there has been a paradigm shift in theoretical neuroscience in which the brain—as a passive processor of sensory information—is now considered an active organ of inference, generating predictions and hypotheses about the causes of its sensations. In this commentary, we try to convey the basic ideas behind this perspective, describe their neurophysiologic underpinnings, and highlight the potential importance of this formulation for clinical neuroscience. The formalism it provides—and the implementation of active inference in the brain—may have the potential to reveal aspects of functional neuroanatomy that are compromised in conditions ranging from Parkinson disease to schizophrenia. In particular, many neurologic and neuropsychiatric conditions may be understandable in terms of a failure to modulate the postsynaptic gain of neuronal populations reporting prediction errors during action and perception. From the perspective of the predictive brain, this represents a failure to encode the precision of—or confidence in—sensory information. We propose that the predictive or inferential perspective on brain function offers novel insights into brain diseases. <s> BIB009
Recent theories of action control suggest that internal models involved during action execution are also engaged during goaldirected action observation BIB002 BIB009 . According to the predictive coding account, low-level visual information is translated into high-level representation of the goal underpinning the observed action through the superior temporal sulcus and fronto-central areas (prediction 1). Then, based on this prior inference about the goal of the observed action, one can predict the motor command of the observed action (prediction 2). Based on this motor command prediction, one can predict the kinematics of the observed person thanks to one's own motor system (prediction 3). Finally, the comparison between the predicted kinematics and the actual observed kinematics will produce a prediction error improving the initial inferred representation of the other's motor command (prediction 2) yielding a more accurate motor command estimate (prediction 4). Likewise, the comparison between the prior predicted motor command (prediction 2) and the new improved motor command estimate (prediction 4) would improve the inferred goal estimate. Thus, one can infer the causes of an observed action by minimizing the prediction errors at the intention, goal, motor and kinematic levels engaged during action observation BIB002 BIB009 . Supporting the predictive coding account, it has been shown we can discriminate other's tiny variations of kinematics from our own motor experience BIB005 . BIB005 presented to participants videos showing either an actor who would next cooperate or compete with another player (not shown) in order to build a tower with small blocks of wood, or who was performing the building task alone, or showing instead point light (in which each point light corresponds to a hand joint) reflecting these same actions. The videos were cut just after the actor had grabbed the wooden block to perform the action. The task of the participants was to categorize the prior intention of the actor (cooperation vs. competition). The results showed that participants succeeded in categorizing the different social intentions both in standard and point light conditions. It has been hypothesized that this ability relied on motor simulation during action observation BIB005 . Indeed, as prior intentions are embodied in kinematics, by simulating observed other-generated actions, one can understand what the observed agent's intention with the help of one's own motor experience  BIB003 . Prior expectation about an agent's intention can modulate observers' correct intention inference BIB006 . For example, when participants had to infer the intention of an observed actor (e.g., to cooperate or to compete), they could not disengage themselves from induced implicit prior thought even when the amount of visual information was sufficient to make relevant predictions. Furthermore, it has been shown individuals can predict an action goal before the action ends, provided that the action conforms to biological motion rules BIB007 . In their study, participants were shown video clips of a point light display (in which each point light corresponds to a hand joint) moving toward a target object. The kinematic pattern of the action was either biological or non-biological. In the biological condition, participants shifted their gaze toward the target object before the end of the action whereas there was no anticipatory behavior in the non-biological condition. Furthermore, in another study, BIB008 induced a transcranial magnetic stimulation (TMS) over either the hand's motor cerebral area or the leg cerebral area of participants looking at movies of point light reaching-grasping actions. They found participants' predictive gaze behavior was slowed down when the motor hand area was stimulated but not when participants had the leg motor area stimulation or without TMS (i.e., in the control condition), arguing for a somatotopical recruitment of observers' motor system during action observation. Hence, during the passive observation of others, motion cues are used to anticipate others' action goals, in accordance with the predictive coding theory. The involvement of our own motor system during action observation is also supported by work on expertise BIB001 BIB004 . For exemple, BIB004 showed free basketball shot movies to participants who had to predict whether the ball would go in or out the basket (or if they did not know) by pressing a specific key. There were three groups of participants: expert basketball players, expert watchers with a similar visual experience, such as coaches or sport journalists, and novice basketball players. The authors showed expert basketball players were better at predicting successful free shots before the actor had thrown the ball using kinematic cues, in comparison with expert watchers and novices. Furthermore, using TMS, they found the basketball shot movies induced an increase of the corticospinal excitability both in the expert player and watcher groups but not in the novice group. Moreover, the observation of the erroneous free shots induced a greater corticospinal excitability than observation of the successful free shots but only in the expert player group. This motor facilitation in the expert player group underlines the existence of a fine-tuned action/observation matching system established through motor practice BIB004 . Finally, neuroimaging data have shown the activation of brain areas wellknown to be involved in predictive mechanisms during othergenerated actions observation was mainly influenced by selfacquired motor skills, such as ballet or capoeira movements BIB001 . Unlike individual actions, joint actions imply that the agents make additional planning to take into consideration other's intentions. They predict the partner's state because her or his sensorimotor information is not available. In accordance with the predictive coding theory, behavioral and neuroimaging data suggest the actions of others are spontaneously mapped onto our own motor system during social interactions, allowing action understanding and prediction. This may be a predisposition selected in the course of evolution to promote easy and efficient social interactions with conspecifics.