When far becomes near: Shared environments activate action simulation

It has been proposed that one means of understanding a person's current behaviour and predicting future actions is by simulating their actions. That is, when another person's actions are observed, similar motor processes are activated in the observer. For example, after observing a reach over an obstacle, a person's subsequent reach trajectory is more curved, reflecting motor priming. Importantly, such motor states are only activated if the observed action is in near (peripersonal) space. However, we demonstrate that when individuals share action environments, simulation of another person's obstacle avoiding reach path takes place even when the action is in far (extrapersonal) space. We propose that action simulation is influenced by factors such as ownership. When an “owned” object is a potential future obstacle, even when it is viewed beyond current action space, simulations are evoked, and these leave a more stable memory capable of influencing future behaviour.     

When far becomes near: shared environments activate action simulation

It has been proposed that one means of understanding a person's current behaviour and predicting future actions is by simulating their actions. That is, when another person's actions are observed, similar motor processes are activated in the observer. For example, after observing a reach over an obstacle, a person's subsequent reach trajectory is more curved, reflecting motor priming. Importantly, such motor states are only activated if the observed action is in near (peripersonal) space. However, we demonstrate that when individuals share action environments, simulation of another person's obstacle avoiding reach path takes place even when the action is in far (extrapersonal) space. We propose that action simulation is influenced by factors such as ownership. When an "owned" object is a potential future obstacle, even when it is viewed beyond current action space, simulations are evoked, and these leave a more stable memory capable of influencing future behaviour.     

Observed reach trajectory influences executed reach kinematics in prehension

Previous studies have demonstrated that the observation of action can modulate motor performance. This literature has focused on manipulating the observed goal of the action, rather than examining whether action observation effects could be elicited by changing observed kinematics alone. In the study presented here, observed reach trajectory kinematics unrelated to the goal of the action were manipulated in order to examine whether observed movement kinematics alone could influence the action of the observer. Participants observed an experimenter grasp a target object using either a normal or an exaggeratedly high reaching action (as though reaching over an invisible obstacle). When participants observed the experimenter perform actions with a high reach trajectory, their own movements took on aspects of the observed action, showing greater wrist height throughout their reaching trajectory than under conditions in which they observed normal reaching actions. The data are discussed in relation to previous findings which suggest that kinematic aspects of observed movements can prime action through kinematic or intention based matching processes.     

Observed reach trajectory influences executed reach kinematics in prehension

Previous studies have demonstrated that the observation of action can modulate motor performance. This literature has focused on manipulating the observed goal of the action, rather than examining whether action observation effects could be elicited by changing observed kinematics alone. In the study presented here, observed reach trajectory kinematics unrelated to the goal of the action were manipulated in order to examine whether observed movement kinematics alone could influence the action of the observer. Participants observed an experimenter grasp a target object using either a normal or an exaggeratedly high reaching action (as though reaching over an invisible obstacle). When participants observed the experimenter perform actions with a high reach trajectory, their own movements took on aspects of the observed action, showing greater wrist height throughout their reaching trajectory than under conditions in which they observed normal reaching actions. The data are discussed in relation to previous findings which suggest that kinematic aspects of observed movements can prime action through kinematic or intention based matching processes.     

The influence of environmental context in interpersonal observation–execution

Cyclical upper-limb movements involuntarily deviate from a primary movement direction when the actor concurrently observes incongruent biological motion. We examined whether environmental context influences such motor interference during interpersonal observation–execution. Participants executed continuous horizontal arm movements while observing congruent horizontal or incongruent curvilinear biological movements with or without the presence of an object positioned as an obstacle or distractor. When participants were observing a curvilinear movement, an object located within the movement space became an obstacle, and, thus, the curvilinear trajectory was essential to reach into horizontal space. When acting as a distractor, or with no object, the curvilinear trajectory was no longer essential. For observing horizontal movements, objects were located at the same relative locations as in the curvilinear movement condition. We found greater involuntary movement deviation when observing curvilinear than horizontal movements. Also, there was an influence of context only when observing horizontal movements, with greater deviation exhibited in the presence of a large obstacle. These findings suggest that the influence of environmental context is underpinned by the (mis-)matching of observed and executed actions as incongruent biological motion is primarily coded via bottom-up sensorimotor processes, whilst the congruent condition incorporates surrounding environmental features to modulate the bottom-up sensorimotor processes.     

The predictive mirror: interactions of mirror and affordance processes during action observation

An important question for the study of social interactions is how the motor actions of others are represented. Research has demonstrated that simply watching someone perform an action activates a similar motor representation in oneself. Key issues include (1) the automaticity of such processes, and (2) the role object affordances play in establishing motor representations of others' actions. Participants were asked to move a lever to the left or right to respond to the grip width of a hand moving across a workspace. Stimulus-response compatibility effects were modulated by two task-irrelevant aspects of the visual stimulus: the observed reach direction and the match between hand-grasp and the affordance evoked by an incidentally presented visual object. These findings demonstrate that the observation of another person's actions automatically evokes sophisticated motor representations that reflect the relationship between actions and objects even when an action is not directed towards an object.     

Predicting others' actions via grasp and gaze: evidence for distinct brain networks

During social interactions, how do we predict what other people are going to do next? One view is that we use our own motor experience to simulate and predict other people's actions. For example, when we see Sally look at a coffee cup or grasp a hammer, our own motor system provides a signal that anticipates her next action. Previous research has typically examined such gaze and grasp-based simulation processes separately, and it is not known whether similar cognitive and brain systems underpin the perception of object-directed gaze and grasp. Here we use functional magnetic resonance imaging to examine to what extent gaze- and grasp-perception rely on common or distinct brain networks. Using a 'peeping window' protocol, we controlled what an observed actor could see and grasp. The actor could peep through one window to see if an object was present and reach through a different window to grasp the object. However, the actor could not peep and grasp at the same time. We compared gaze and grasp conditions where an object was present with matched conditions where the object was absent. When participants observed another person gaze at an object, left anterior inferior parietal lobule (aIPL) and parietal operculum showed a greater response than when the object was absent. In contrast, when participants observed the actor grasp an object, premotor, posterior parietal, fusiform and middle occipital brain regions showed a greater response than when the object was absent. These results point towards a division in the neural substrates for different types of motor simulation. We suggest that left aIPL and parietal operculum are involved in a predictive process that signals a future hand interaction with an object based on another person's eye gaze, whereas a broader set of brain areas, including parts of the action observation network, are engaged during observation of an ongoing object-directed hand action.     

Learning associations between action and perception: effects of incompatible training on body part and spatial priming

Observation of another person executing an action primes the same action in the observer's motor system. Recent evidence has shown that these priming effects are flexible, where training of new associations, such as making a foot response when viewing a moving hand, can reduce standard action priming effects (Gillmeister, Catmur, Liepelt, Brass, & Heyes, 2008). Previously, these effects were obtained after explicit learning tasks in which the trained action was cued by the content of a visual stimulus. Here we report similar learning processes in an implicit task in which the participant's action is self-selected, and subsequent visual effects are determined by the nature of that action. Importantly, we show that these learning processes are specific to associations between actions and viewed body parts, in that incompatible spatial training did not influence body part or spatial priming effects. Our results are consistent with models of visuomotor learning that place particular emphasis on the repeated experience of watching oneself perform an action.     

Self produced and observed actions influence emotion: the roles of action fluency and eye gaze

Affective responses to objects can be influenced by cognitive processes such as perceptual fluency. Here we investigated whether the quality of motor interaction with an object influences affective response to the object. Participants grasped and moved objects using either a fluent action or a non-fluent action (avoiding an obstacle). Liking ratings were higher for objects in the fluent condition. Two further studies investigated whether the fluency of another person’s actions influences affective response. Observers watched movie clips of the motor actions described above, in conditions where the observed actor could be seen to be looking towards the grasped object, or where the actor’s head and gaze were not visible. Two results were observed: First, when the actor’s gaze cannot be seen, liking ratings of the objects are reduced. Second, action fluency of observed actions does influence liking ratings, but only when the actor’s gaze towards the object is visible. These findings provide supporting evidence for the important role of observed eye gaze in action simulation, and demonstrate that non-emotive actions can evoke empathic states in observers. This research was supported by Economic and Social Research Council grant RES-000-23-0429 awarded to S. P. Tipper and A. E. Hayes.     

Seeing the world through another person’s eyes: Simulating selective attention via action observation

Selective attention is usually considered an egocentric mechanism, biasing sensory information based on its behavioural relevance to oneself. This study provides evidence for an equivalent allocentric mechanism that allows passive observers to selectively attend to information from the perspective of another person. In a negative priming task, participants reached for a red target stimulus whilst ignoring a green distractor. Distractors located close to their hand were inhibited strongly, consistent with an egocentric frame of reference. When participants took turns with another person, the pattern of negative priming shifted to an allocentric frame of reference: locations close to the hand of the observed agent (but far away from the participant’s hand) were inhibited strongly. This suggests that witnessing another’s action leads the observer to simulate the same selective attention mechanisms such that they effectively perceive their surroundings from the other person’s perspective.     

On the dynamics of action representations evoked by names of manipulable objects

Two classes of hand action representations are shown to be activated by listening to the name of a manipulable object (e.g., cellphone). The functional action associated with the proper use of an object is evoked soon after the onset of its name, as indicated by primed execution of that action. Priming is sustained throughout the duration of the word's enunciation. Volumetric actions (those used to simply lift an object) show a negative priming effect at the onset of a word, followed by a short-lived positive priming effect. This time-course pattern is explained by a dual-process mechanism involving frontal and parietal lobes for resolving conflict between candidate motor responses. Both types of action representations are proposed to be part of the conceptual knowledge recruited when the name of a manipulable object is encountered, although functional actions play a more central role in the representation of lexical concepts.     

Can we correctly perceive the reaching range of others?

Little is known about our ability to predict the motor capacities of other people. This study explored how observers perceive the reaching range of another person by asking them to judge the reachability of a moving object. Experiments 1 and 2 found that observers overestimated the reaching ranges of both short and tall people. Estimates were larger when objects moved towards rather than away from the person. Experiment 3 showed that perceived reaching range depended on the observer's viewing perspective. Compared with previous findings, these results suggest that observers use different cognitive operations to mentally simulate actions for themselves vs. others. They also inform the current debate about motor imagery and action understanding.     

Verbal social primes alter motor contagion during action observation

We investigated whether prosocial and nonsocial word primes prior to action observation modify subsequent initiation and execution of the observer's own reach-to-grasp actions. Participants observed a model performing exaggeratedly curved (vertical deviation) or natural straight reaches to a vertical dowel and always performed a straight reach to a dowel themselves. Observing curved movements slowed initiation times and increased the vertical deviation of the participants’ movements. Observing curved movements enhanced vertical deviation only in the prosocial word primes condition. We suggest that social context priming can modulate initiation of movement as well as the extent of motor contagion (in this case, the extent of vertical deviation) between model and observer.     

When do we simulate non-human agents? Dissociating communicative and non-communicative actions

There is strong evidence that we automatically simulate observed behavior in our motor system. Previous research suggests that this simulation process depends on whether we observe a human or a non-human agent. Measuring a motor priming effect, this study investigated the question of whether agent-sensitivity of motor simulation depends on the specific action observed. Participants saw pictures depicting end positions of different actions on a screen. All postures featured either a human or non-human agent. Participants had to produce the matching action with their left or right hand depending on the hand presented on the screen. Three different actions were displayed: a communicative action (emblem), a transitive (goal-directed) action and an intransitive action. We found motor priming effects of similar size for human and non-human agents for transitive and intransitive actions. However, the motor priming effect for communicative actions was present for the human agent, but absent for the non-human agent. These findings suggest that biological tuning of motor simulation is highly action-selective and depends on whether the observed behavior appears to be driven by a reasonable goal.     

Do action goals mediate social inhibition of return?

Social inhibition of return is the phenomenon whereby an individual is slower to reach to locations to which another individual has recently responded. Although this suggests that an observer represents another person's action, little is known about which aspects of the action are encoded. The present work describes a series of three experiments examining whether social inhibition of return represents the endpoint goal of the action, i.e., is 'goal based'. Pairs of participants sat opposite to one another and alternated responses to a cued or non-cued object presented on a table top. Importantly, either the two participants performed the same interaction with the object or a different interaction. Although all our experiments showed social inhibition of return, the size of the effect was not modulated according to whether each participant had the same or different goal. We conclude that although the mechanisms giving rise to social inhibition of return do encode some aspects of a response they do not code for terminal action goals.     

One‐year‐old infants use teleological representations of actions productively

Two experiments investigated whether infants represent goal‐directed actions of others in a way that allows them to draw inferences to unobserved states of affairs (such as unseen goal states or occluded obstacles). We measured looking times to assess violation of infants' expectations upon perceiving either a change in the actions of computer‐animated figures or in the context of such actions. The first experiment tested whether infants would attribute a goal to an action that they had not seen completed. The second experiment tested whether infants would infer from an observed action the presence of an occluded object that functions as an obstacle. The looking time patterns of 12‐month‐olds indicated that they were able to make both types of inferences, while 9‐month‐olds failed in both tasks. These results demonstrate that, by the end of the first year of life, infants use the principle of rational action not only for the interpretation and prediction of goal‐directed actions, but also for making productive inferences about unseen aspects of their context. We discuss the underlying mechanisms that may be involved in the developmental change from 9 to 12 months of age in the ability to infer hypothetical (unseen) states of affairs in teleological action representations.     

I don't get you. Action observation effects inverted by kinematic variation

Recent studies have reported an intricate interplay between affordance and mirror effects (the imitation of another agent) when participants attend to the concurrent presentation of an object and another agent interacting with it. In the present paper, we compare two experimental settings in which an observed action was presented as a prime for a task involving the categorization of a graspable object. In experiment 1a, the action depicted a reach and grasp gesture whereas in experiment 1b, only the reach phase was presented. This modification led to very different outcomes. Experiment 1a reflected the traditional imitation effect elicited by human motion. Conversely, experiment 1b showed the facilitation of contralateral responses. Affordance effects were found in experiment 1a only for the RVF. Our results support the view that motor simulation processes underlying imitation or joint actions are extremely sensitive to specific phase kinematics.     

Eye movements may cause motor contagion effects

When a person executes a movement, the movement is more errorful while observing another person’s actions that are incongruent rather than congruent with the executed action. This effect is known as “motor contagion”. Accounts of this effect are often grounded in simulation mechanisms: increased movement error emerges because the motor codes associated with observed actions compete with motor codes of the goal action. It is also possible, however, that the increased movement error is linked to eye movements that are executed simultaneously with the hand movement because oculomotor and manual-motor systems are highly interconnected. In the present study, participants performed a motor contagion task in which they executed horizontal arm movements while observing a model making either vertical (incongruent) or horizontal (congruent) movements under three conditions: no instruction, maintain central fixation, or track the model’s hand with the eyes. A significant motor contagion-like effect was only found in the ‘track’ condition. Thus, ‘motor contagion’ in the present task may be an artifact of simultaneously executed incongruent eye movements. These data are discussed in the context of stimulation and associative learning theories, and raise eye movements as a critical methodological consideration for future work on motor contagion.     

A perceiver’s own abilities influence perception,even when observing others

Perceptual judgments of objects, such as judgments of their size, distance, and speed, are influenced by the perceiver’s ability to act on these objects. For example, objects that are easier to block appear to be moving slower than objects that are more difficult to block. These effects are known as action-specific effects. Recent research has found similar patterns when a person observes someone else act: When the other person’s task is more difficult, objects look farther away and faster to the observer, whereas when the other person’s task is easier, the objects look closer and slower to the observer. These previous findings that another person’s ability penetrates into perceptual judgments challenge the idea that action-specific effects are specific to the perceiver’s own abilities. However, in the present study, we show that the apparent effects of another person’s ability on the observer’s judgments are actually due to the observer’s own abilities as if he or she was in the other person’s situation. This implicates a type of self-projection motor simulation mechanism. The results also preserve the critical idea that action-specific effects are perceiver specific and, consequently, that they could be adaptive for planning future actions.     

Activation of action rules in action observation

Visually perceiving an action may activate corresponding motor programs. This automatic motor activation can occur both for higher level (i.e., the goal of an action) and for lower level (i.e., the specific effector with which it is executed) aspects of an action. The authors used a tool-use action paradigm to experimentally dissociate priming effects for observing the target, the movement, or the target-to-movement mapping of a tool-use action. In 3 experiments, participants took turns in acting, observing the tool-use action of another person in trial n-1, and executing an action in trial n. Trial transitions from n-1 to n were manipulated in 4 conditions with (a) mapping repeated and movement and target changed, (b) target repeated and movement and mapping changed, (c) movement repeated and target and mapping changed, or (d) all components repeated. Results indicate priming effects for repeating the target-to-movement mapping (i.e., the action rule) of a tool-use action and suggest that a rather abstract action schema is activated during action observation.