Evidence for we-representations during joint action planning

Synchrony Across Brains

Second-person neuroscience focuses on studying the behavioral and neuronal mechanisms of real-time social interactions within single and across interacting brains. In this review article, we describe the developments that have been undertaken to study socially interactive phenomena and the behavioral and neurobiological processes that extend across interaction partners. More specifically, we focus on the role that synchrony across brains plays in enabling and facilitating social interaction and communication and in shaping social coordination and learning, and we consider how reduced synchrony across brains may constitute a core feature of psychopathology.

Coordinated social interactions are supported by integrated neural representations

Joint actions are defined as coordinated interactions of two or more agents toward a shared goal, often requiring different and complementary individual contributions. However, how humans can successfully act together without the interfering effects of observing incongruent movements is still largely unknown. It has been proposed that interpersonal predictive processes are at play to allow the formation of a Dyadic Motor Plan, encompassing both agents' shares. Yet, direct empirical support for such an integrated motor plan is still limited. In this study, we aimed at testing the properties of these anticipated representations. We collected electroencephalography data while human participants (N = 36; 27 females) drew shapes simultaneously to a virtual partner, in two social contexts: either they had to synchronize and act jointly or they performed the movements alongside, but independently. We adopted a multivariate approach to show that the social context influenced how the upcoming action of the partner is anticipated during the interval preceding the movement. We found evidence that acting jointly induces an encoding of the partner's action that is strongly intertwined with the participant's action, supporting the hypothesis of an integrative motor plan in joint but not in parallel actions.

Motor-related cortical oscillations distinguish one's own from a partner's contributions to a joint action

The ability to distinguish between one's own and others' actions is a requirement for successful joint action. Such a distinction might be supported by dissociable motor activity underlying each partner's individual contributions to the joint action. However, little research has directly compared motor activity associated with one's own vs. others' actions during joint action. The current study investigated whether motor-related cortical oscillations distinguish between self- and partner-produced actions when partners take turns producing taps to meet a joint timing goal. Across two experiments, the degree of beta suppression differentiated one's own from a partner's actions, with more suppression occurring during one's own actions than during a partner's actions. Self-partner differences in mu suppression were also evident, particularly when partners produced actions in succession. Increased beta suppression was also observed during partners' actions when they were followed by one's own actions, suggesting that the coordination demands imposed by the joint action could affect the pattern of beta reactivity during a turn-taking joint action. Together, these findings demonstrate that dynamic patterns of motor activity underpin successful joint action and that periods of distinct motor activity are associated with one's own contributions to a joint action.

Me or we? Action-outcome learning in synchronous joint action

Goal-directed behaviour requires mental representations that encode instrumental relationships between actions and their outcomes. The present study investigated how people acquire representations of joint actions where co-actors perform synchronized action contributions to produce joint outcomes in the environment. Adapting an experimental procedure to assess individual action-outcome learning, we tested whether co-acting individuals link jointly produced action outcomes to individual-level features of their own action contributions or to group-level features of their joint action instead. In a learning phase, pairs of participants produced musical chords by synchronizing individual key press responses. In a subsequent test phase, the previously produced chords were presented as imperative stimuli requiring forced-choice responses by both pair members. Stimulus-response mappings were systematically manipulated to be either compatible or incompatible with the individual and joint action-outcome mappings of the preceding learning phase. Only joint but not individual compatibility was found to modulate participants' performance in the test phase. Yet, opposite to predictions of associative accounts of action-outcome learning, jointly incompatible mappings between learning and test phase resulted in better performance. We discuss a possible explanation of this finding, proposing that pairs' group-level learning experience modulated how participants encoded ambiguous task instructions in the test phase. Our findings inform current debates about mechanistic explanations of action-outcome learning effects and provide novel evidence that joint action is supported by dedicated mental representations encoding own and others' actions on a group level.

Spatial Response Discrimination May Elicit a Simon Effect on a Non-Complementary Task

When paired participants are each assigned a complementary half of the Simon task, a joint Simon effect (JSE) has been observed. Co-representation, a cognitive representation of not only one's own task but also that of the co-actor, has been one of several proposed mechanisms in the JSE. Using the response-discrimination hypothesis as a framework, we tested whether it was sufficient to highlight alternative task keys in a two-person setting in which a non-complementary task was completed to elicit a Simon effect (SE). In our design, the participant's role was to perform the Go/No-Go Simon task and the co-actor's role was to initiate each trial for the participant. In one two-person setting participant group (SK group), the same task key was assigned to both the participant and the co-actor; another group (OK) was assigned spatially opposite task keys. In a third group (joint setting, TS group), the standard joint Simon task was also completed to verify that a JSE could be replicated. We hypothesized that an SE would be elicited in the OK group, since opposite task keys would uniquely promote spatial coding. We found a weak but marginally significant SE in the OK group but not in the SK group. These results suggest that, on a non-complementary task, response discrimination may contribute to the emergence of a SE in a two-person setting, while it does not have the same impact as a complementary task completed in a joint setting (TS group) that may afford more robust response representations that reveal the enhanced so-called JSE.

Synchrony Influences Estimates of Cooperation in a Public-Goods Game

Benefiting from a cooperative interaction requires people to estimate how cooperatively other members of a group will act so that they can calibrate their own behavior accordingly. We investigated whether the synchrony of a group's actions influences observers' estimates of cooperation. Participants (recruited through Prolific) watched animations of actors deciding how much to donate in a public-goods game and using a mouse to drag donations to a public pot. Participants then estimated how much was in the pot in total (as an index of how cooperative they thought the group members were). Experiment 1 (N = 136 adults) manipulated the synchrony between players' decision-making time, and Experiment 2 (N = 136 adults) manipulated the synchrony between players' decision-implementing movements. For both experiments, estimates of how much was in the pot were higher for synchronous than asynchronous groups, demonstrating that the temporal dynamics of an interaction contain signals of a group's level of cooperativity.

Searching for the Metaverse: Neuroscience of Physical and Digital Communities

What distinguishes real-world communities from their online counterparts? Social and cognitive neuroscience research on social networks and collective intentionality will be used in the article to answer this question. Physical communities are born in places. And places engage "we-mode" neurobiological and cognitive processes as behavioral synchrony, shared attention, deliberate attunement, interbrain synchronization, and so on, which create coherent social networks of very different individuals who are supported by a "wisdom of crowd." Digital technologies remove physical boundaries, giving people more freedom to choose their activities and groups. At the same time, however, the lack of physical co-presence of community members significantly reduces their possibility of activating "we-mode" cognitive processes and social motivation. Because of this, unlike physical communities that allow interaction between people from varied origins and stories, digital communities are always made up of people who have the same interests and knowledge (communities of practice). This new situation disrupts the "wisdom of crowd," making the community more radical and less accurate (polarization effect), allowing influential users to wield disproportionate influence over the group's beliefs, and producing inequalities in the distribution of social capital. However, a new emergent technology-the Metaverse-has the potential to reverse this trend. Several studies have revealed that virtual and augmented reality-the major technologies underlying the Metaverse-can engage the same neurobiological and cognitive "we-mode" processes as real-world environments. If the many flaws in this technology are fixed, it might encourage people to engage in more meaningful and constructive interactions in online communities.

Theory of collective mind

Theory of mind research has traditionally focused on the ascription of mental states to a single individual. Here, we introduce a theory of collective mind: the ascription of a unified mental state to a group of agents with convergent experiences. Rather than differentiation between one's personal perspective and that of another agent, a theory of collective mind requires perspectival unification across agents. We review recent scholarship across the cognitive sciences concerning the conceptual foundations of collective mind representations and their empirical induction through the synchronous arrival of shared information. Research suggests that representations of a collective mind cause psychological amplification of co-attended stimuli, create relational bonds, and increase cooperation, among co-attendees.

Neuromodulation of the Left Inferior Frontal Cortex Affects Social Monitoring during Motor Interactions

Motor interactions require observing and monitoring a partner's performance as the interaction unfolds. Studies in monkeys suggest that this form of social monitoring might be mediated by the activity of the ventral premotor cortex (vPMc), a critical brain region in action observation and motor planning. Our previous fMRI studies in humans showed that the left vPMc is indeed recruited during social monitoring, but its causal role is unexplored. In three experiments, we applied online anodal or cathodal transcranial direct current stimulation over the left lateral frontal cortex during a music-like interactive task to test the hypothesis that neuromodulation of the left vPMc affects participants' performance when a partner violates the agent's expectations. Participants played short musical sequences together with a virtual partner by playing one note each in turn-taking. In 50% of the trials, the partner violated the participant's expectations by generating the correct note through an unexpected movement. During sham stimulation, the partner's unexpected behavior led to a slowdown in the participant's performance (observation-induced posterror slowing). A significant interaction with the stimulation type showed that cathodal and anodal transcranial direct current stimulation induced modulation of the observation-induced posterror slowing in opposite directions by reducing or enhancing it, respectively. Cathodal stimulation significantly reduced the effect compared to sham stimulation. No effect of neuromodulation was found when the partner behaved as expected or when the observed violation occurred within a context that was perceptually matched but noninteractive in nature. These results provide evidence for the critical causal role that the left vPMc might play in social monitoring during motor interactions, possibly through the interplay with other brain regions in the posterior medial frontal cortex.

Spontaneous dyadic behaviour predicts the emergence of interpersonal neural synchrony

Synchronization of neural activity across brains - interpersonal neural synchrony (INS) - is emerging as a powerful marker of social interaction that predicts success of multi-person coordination, communication, and cooperation. As the origins of INS are poorly understood, we tested whether and how INS might emerge from spontaneous dyadic behavior. We recorded neural activity (EEG) and human behavior (full-body kinematics, eye movements and facial expressions) while dyads of participants were instructed to look at each other without speaking or making co-verbal gestures. We made four fundamental observations. First, despite the absence of a structured social task, INS emerged spontaneously only when participants were able to see each other. Second, we show that such spontaneous INS, comprising specific spectral and topographic profiles, did not merely reflect intra-personal modulations of neural activity, but it rather reflected real-time and dyad-specific coupling of neural activities. Third, using state-of-art video-image processing and deep learning, we extracted the temporal unfolding of three notable social behavioral cues - body movement, eye contact, and smiling - and demonstrated that these behaviors also spontaneously synchronized within dyads. Fourth, we probed the correlates of INS in such synchronized social behaviors. Using cross-correlation and Granger causality analyses, we show that synchronized social behaviors anticipate and in fact Granger cause INS. These results provide proof-of-concept evidence for studying interpersonal neural and behavioral synchrony under natural and unconstrained conditions. Most importantly, the results suggest that INS could be conceptualized as an emergent property of two coupled neural systems: an entrainment phenomenon, promoted by real-time dyadic behavior.

Not just in sync: Relations between partners' actions influence the sense of joint agency during joint action

When people perform joint actions together, they often experience a sense of joint agency ("we did that together"). The current study investigated whether relations between partners' actions within joint actions that require precise interpersonal synchrony influence joint agency, above and beyond the degree of synchrony partners achieve. We employed a mixed-methods approach that combined a quantitative experiment with a qualitative analysis of post-experiment interviews. Partners produced synchronized tone sequences that comprised either constant pitch sequences (simple temporal alignment between partners' actions) or musical duets (complex metrical and harmonic relations between partners' actions). Participants reported stronger joint agency for duets than constant pitches, when comparing trials with equally good synchronization. Post-experiment interviews revealed that joint agency was also influenced by participants' knowledge of the music and their perceptions of task performance, difficulty, and enjoyability. These findings further our understanding of joint agency for joint actions that require precise interpersonal synchrony.

Emergent and planned interpersonal synchronization are both sensitive to 'tempo aftereffect contagion'

Interpersonal synchronization is fundamental for motor coordination during social interactions. Discerning emergent (entrainment) from planned synchronization represents a non-trivial issue in visually bonded individuals acting together, as well as assessing whether inter-individual differences, e.g., in autistic traits, modulate both types of synchronization. In a visuomotor finger-tapping task, two participants replicated a target tempo either synchronizing ('joint' condition) or not ('non-interactive' condition, 'non-int') with each other. One participant was exposed ('induced') to tempo aftereffect (a medium tempo seems faster or slower after exposure to slower or faster inducing tempi), but not the other participant ('not induced'); thus they had different timing perceptions of the same target. We assessed to what degree emergent and/or planned synchronization affected dyads by analyzing inter-tap-intervals, synchronization indexes, and cross-correlation coefficients. Results revealed a 'tempo aftereffect contagion': inter-tap-intervals of both induced and not-induced participants showed aftereffect in both the joint and non-int conditions. Moreover, aftereffects did not correlate across conditions suggesting they might be due to (at least in part) different processes, but the propensity for tempo aftereffect contagion correlated with individuals' autistic traits only in the non-int condition. Finally, participants co-adjusted their tapping more in the joint condition than in the non-int one, as confirmed by higher synchronization indexes and the mutual adaptation pattern of cross-correlation coefficients. Altogether, these results show the subtle interplay between emergent and planned interpersonal synchronization mechanisms that act on a millisecond timescale independently from synching or not with the partner.

Cortico-cerebellar audio-motor regions coordinate self and other in musical joint action

Joint music performance requires flexible sensorimotor coordination between self and other. Cognitive and sensory parameters of joint action-such as shared knowledge or temporal (a)synchrony-influence this coordination by shifting the balance between self-other segregation and integration. To investigate the neural bases of these parameters and their interaction during joint action, we asked pianists to play on an MR-compatible piano, in duet with a partner outside of the scanner room. Motor knowledge of the partner's musical part and the temporal compatibility of the partner's action feedback were manipulated. First, we found stronger activity and functional connectivity within cortico-cerebellar audio-motor networks when pianists had practiced their partner's part before. This indicates that they simulated and anticipated the auditory feedback of the partner by virtue of an internal model. Second, we observed stronger cerebellar activity and reduced behavioral adaptation when pianists encountered subtle asynchronies between these model-based anticipations and the perceived sensory outcome of (familiar) partner actions, indicating a shift towards self-other segregation. These combined findings demonstrate that cortico-cerebellar audio-motor networks link motor knowledge and other-produced sounds depending on cognitive and sensory factors of the joint performance, and play a crucial role in balancing self-other integration and segregation.

Encoding interactive scripts at 10 months of age

Understanding action-reaction associations that give origin to interactive scripts (e.g., give-and-take interactions) is essential for appreciating social exchanges. However, studies on infants' action understanding have mainly investigated the case of actions performed by individual agents. Moreover, although extensive literature has explored infants' comprehension of action-effect relationships in object functioning, no study has addressed whether it also plays a role when observing social interactions, an issue we addressed here. In a first study, 10-month-old infants observed short videos of dyadic exchanges. We investigated whether they were able to link specific human gestures directed toward another person to specific vocal reactions in the receiver. We used a double-habituation paradigm in which infants were sequentially habituated to two specific action-reaction associations. In the test phase, infants watched one of the two habituated (Familiar) videos, a video with a reversed action-reaction association (Violation), and a Novel video. Results showed that the infants looked longer at both the Novel and Violation test trials than at the Familiar test trials. In a control study, we show that these results could not be accounted for by associative learning; indeed, learning of the action-reaction association did not occur when the vocalization was not produced by the receiver but only contingent on the agent's action. Thus, we show that 10-month-old infants can encode specific social action-effect relationships during the observation of dyadic interactions and that the interactivity of the social context may be critical to shaping young infants' understanding of others' behaviors.

Inter-individual coordination in walking chimpanzees

Humans, like many other animals, live in groups and coordinate actions with others in social settings.1 Such interpersonal coordination may emerge unconsciously and when the goal is not the coordination of movements, as when falling into the same rhythm when walking together.2 Although one of our closest living relatives, the chimpanzee (Pan troglodytes), shows the ability to succeed in complex joint action tasks where coordination is the goal,3 little is known about simpler forms of joint action. Here, we examine whether chimpanzees spontaneously synchronize their actions with conspecifics while walking together. We collected data on individual walking behavior of two groups of chimpanzees under semi-natural conditions. In addition, we assessed social relationships to investigate potential effects on the strength of coordination. When walking with a conspecific, individuals walked faster than when alone. The relative phase was symmetrically distributed around 0° with the highest frequencies around 0, indicating a tendency to coordinate actions. Further, coordination was stronger when walking with a partner compared with two individuals walking independently. Although the inter-limb entrainment was more pronounced between individuals of similar age as a proxy for height, it was not affected by the kinship or bonding status of the walkers or the behaviors they engaged in immediately after the walk. We conclude that chimpanzees adapt their individual behavior to temporally coordinate actions with others, which might provide a basis for engaging in other more complex forms of joint action. This spontaneous form of inter-individual coordination, often called entrainment, is thus shared with humans.

Distinct neural couplings to shared goal and action coordination in joint action: evidence based on fNIRS hyperscanning

Joint action is central to human nature, enabling individuals to coordinate in time and space to achieve a joint outcome. Such interaction typically involves two key elements: shared goal and action coordination. Yet, the substrates entrained to these two components in joint action remained unclear. In the current study, dyads performed two tasks involving both sharing goal and action coordination, i.e. complementary joint action and imitative joint action, a task only involving shared goal and a task only involving action coordination, while their brain activities were recorded by the functional near-infrared spectroscopy hyperscanning technique. The results showed that both complementary and imitative joint action (i.e. involving shared goal and action coordination) elicited better behavioral performance than the task only involving shared goal/action coordination. We observed that the interbrain synchronization (IBS) at the right inferior frontal cortex (IFC) entrained more to shared goal, while left-IFC IBS entrained more to action coordination. We also observed that the right-IFC IBS was greater during completing a complementary action than an imitative action. Our results suggest that IFC plays an important role in joint action, with distinct lateralization for the sub-components of joint action.

The sense of agency in joint action: An integrative review

When people perform joint actions together, their individual actions (e.g., moving one end of a heavy couch) must be coordinated to achieve a collective goal (e.g., moving the couch across the room). Joint actions pose unique challenges for understanding people's sense of agency, because each person engaged in the joint action can have a sense of agency not only at the individual level (a sense that "I moved my end of the couch" or "My partner moved their end of the couch"), but also at the collective level (a sense that "We moved the couch together"). This review surveys research that has examined people's sense of agency in joint action, including explicit judgments of agency, implicit measures of agency, and first-hand accounts of agency in real-world settings. The review provides a comprehensive summary of the factors that influence individual- and collective-level agency in joint action; reveals the progress that has been made toward understanding different forms of collective-level agency in joint action, including the sense that agency is shared among co-actors and the sense that co-actors are acting as a single unit; and synthesizes evidence concerning the relationships between different measures of implicit agency and individual- versus collective-level agency in joint action. The review concludes by highlighting numerous outstanding questions and promising avenues for future research.

Intra-individual behavioural and neural signatures of audience effects and interactions in a mirror-game paradigm

We often perform actions while observed by others, yet the behavioural and neural signatures of audience effects remain understudied. Performing actions while being observed has been shown to result in more emphasized movements in musicians and dancers, as well as during communicative actions. Here, we investigate the behavioural and neural mechanisms of observed actions in relation to individual actions in isolation and interactive joint actions. Movement kinematics and EEG were recorded in 42 participants (21 pairs) during a mirror-game paradigm, while participants produced improvised movements alone, while observed by a partner, or by synchronizing movements with the partner. Participants produced largest movements when being observed, and observed actors and dyads in interaction produced slower and less variable movements in contrast with acting alone. On a neural level, we observed increased mu suppression during interaction, as well as to a lesser extent during observed actions, relative to individual actions. Moreover, we observed increased widespread functional brain connectivity during observed actions relative to both individual and interactive actions, suggesting increased intra-individual monitoring and action-perception integration as a result of audience effects. These results suggest that observed actors take observers into account in their action plans by increasing self-monitoring; on a behavioural level, observed actions are similar to emergent interactive actions, characterized by slower and more predictable movements.

Joint control of visually guided actions involves concordant increases in behavioural and neural coupling

It is often necessary for individuals to coordinate their actions with others. In the real world, joint actions rely on the direct observation of co-actors and rhythmic cues. But how are joint actions coordinated when such cues are unavailable? To address this question, we recorded brain activity while pairs of participants guided a cursor to a target either individually (solo control) or together with a partner (joint control) from whom they were physically and visibly separated. Behavioural patterns revealed that joint action involved real-time coordination between co-actors and improved accuracy for the lower performing co-actor. Concurrent neural recordings and eye tracking revealed that joint control affected cognitive processing across multiple stages. Joint control involved increases in both behavioural and neural coupling - both quantified as interpersonal correlations - peaking at action completion. Correspondingly, a neural offset response acted as a mechanism for and marker of interpersonal neural coupling, underpinning successful joint actions.

Goal sharing with others modulates the sense of agency and motor accuracy in social contexts

Sense of agency (SoA), the feeling of control over one’s own actions and their effects, is fundamental to goal-directed actions at the individual level and may constitute a cornerstone of everyday life, including cooperative behavior (i.e., goal sharing). Previous studies have demonstrated that goal sharing can activate the motor prediction of both agent’s action and partner’s action in joint-action tasks. Moreover, given that from an SoA perspective, predictive processes are an essential basis, there is a possibility that goal sharing may modulate SoA. However, the possibility for goal sharing to modulate SoA remains unclear. This study aimed to investigate whether goal sharing modulates the intentional binding (IB) effect (a method that can quantitatively measure SoA) of self-generated and observed partner’s actions and improves motor accuracy. Participants were required to stop a circular horizontal moving object by pressing a key when the object reaches the center of a target in a social situation. This task measured IB by having participants estimate the time interval between action and effect in several 100 milliseconds, with shorter time interval estimations indicating enhancement of SoA. Participants were randomly divided into 13 Cooperative groups (goal sharing) and 13 Independent groups (non-goal sharing). Cooperative groups were instructed to perform the task together, while Independent groups did so individually. Participants estimated the time interval between them by pressing the key and hearing the corresponding sound (Self-generated action) and the other person pressing the key and hearing the sound (Observed action). Our results indicated that goal sharing improved motor accuracy and enhanced both the IB of Self-generated and Observed actions compared to non-goal sharing. We suggest that SoA can be modulated by goal sharing in specific social contexts.

Mechanisms for mutual support in motor interactions

What is the key to successful interaction? Is it sufficient to represent a common goal, or does the way our partner achieves that goal count as well? How do we react when our partner misbehaves? We used a turn-taking music-like task requiring participants to play sequences of notes together with a partner, and we investigated how people adapt to a partner's error that violates their expectations. Errors consisted of either playing a wrong note of a sequence that the agents were playing together (thus preventing the achievement of the joint goal) or playing the expected note with an unexpected action. In both cases, we found post-error slowing and inaccuracy suggesting the participants' implicit tendency to correct the partner's error and produce the action that the partner should have done. We argue that these "joint" monitoring processes depend on the motor predictions made within a (dyadic) motor plan and may represent a basic mechanism for mutual support in motor interactions.

Progress in Joint-Action Research

Humans have a striking ability to coordinate their actions with each other to achieve joint goals. The tight interpersonal coordination that characterizes joint actions is achieved through processes that help with preparing for joint action as well as processes that are active while joint actions are being performed. To prepare for joint action, partners form representations of each other’s actions and tasks and the relation between them. This enables them to predict each other’s upcoming actions, which, in turn, facilitates coordination. While performing joint actions, partners’ coordination is maintained by (a) monitoring whether individual and joint outcomes correspond to what was planned, (b) predicting partners’ action parameters on the basis of familiarity with their individual actions, (c) communicating task-relevant information unknown to partners in an action-based fashion, and (d) relying on coupling of predictions through dense perceptual-information flow between coactors. The next challenge for the field of joint action is to generate an integrated perspective that links coordination mechanisms to normative, evolutionary, and communicative frameworks.

Emergent Shared Intentions Support Coordination During Collective Musical Improvisations

Human interactions are often improvised rather than scripted, which suggests that efficient coordination can emerge even when collective plans are largely underspecified. One possibility is that such forms of coordination primarily rely on mutual influences between interactive partners, and on perception-action couplings such as entrainment or mimicry. Yet some forms of improvised joint actions appear difficult to explain solely by appealing to these emergent mechanisms. Here, we focus on collective free improvisation, a form of highly unplanned creative practice where both agents' subjective reports and the complexity of their interactions suggest that shared intentions may sometimes emerge to support coordination during the course of the improvisation, even in the absence of verbal communication. In four experiments, we show that shared intentions spontaneously emerge during collective musical improvisations, and that they foster coordination on multiple levels, over and beyond the mere influence of shared information. We also show that musicians deploy communicative strategies to manifest and propagate their intentions within the group, and that this predicts better coordination. Overall, our results suggest that improvised and scripted joint actions are more continuous with one another than it first seems, and that they differ merely in the extent to which they rely on emergent or planned coordination mechanisms.

The motor-related brain activity that supports joint action: A review

Recent years have seen a rapid increase in research investigating the motor-related brain activity that supports joint action. This research has employed a variety of joint action tasks and an array of neuroimaging techniques, including fMRI, fNIRS, EEG, and TMS. In this review, we provide an overview of this research to delineate what is known about the motor-related brain activity that contributes to joint action and to highlight key questions for future research. Taken together, the surveyed research supports three major conclusions. First, the mere presence of a joint action context is sufficient to modulate motor activity elicited by observing others' actions. Second, joint action is supported by dissociable motor activity associated with a person's own actions, their partner's actions, and the joint action, and by between-brain coupling of motor-related oscillatory activity. Third, the structure of a joint action modulates the motor activity involved: Unique motor activity is associated with performing joint actions comprised of complementary actions and with holding the roles of leader and follower within a joint action. We conclude the review by highlighting overarching themes and key questions for future research.

Strategic Self-Regulation in Groups: Collective Implementation Intentions Help Cooperate When Cooperation Is Called for

Groups need contributions that are personally costly to their members. Such cooperation is only adaptive when others cooperate as well, as unconditional cooperation may incur high costs to the individual. We argue that individuals can use We-if-then plans (collective implementation intentions, cIIs) to regulate their group-directed behavior strategically, helping them to cooperate selectively with group members in the situation planned for. In line with this prediction, a cII to consider group earnings increased cooperative decisions in a prisoners' dilemma game when playing against another group member but not when playing against a stranger (i.e., non-group member). Moreover, cIIs to cooperate in the prisoners' dilemma game did not increase cooperation in a structurally similar investment game that participants had not planned for. We discuss the role of collective planning in solving social dilemmas.

The effect of co-actor group membership on the social inhibition of return effect

Being part of a group is a crucial factor in human social interaction. In the current study we explored whether group membership affects reflexive automatic cognitive functioning, and specifically the social inhibition of return effect (SIOR; Welsh et al., 2005). SIOR is characterized by slower reaction times (RTs) to a location already searched by another agent. To examine whether group membership modulates SIOR, we recruited Muslim and Jewish students from the University of Haifa to perform a task with either an in-group member or an out-group member. Both IOR and SIOR were suggested to act as a foraging facilitator (Klein, 2000; Welsh et al., 2005). Accordingly, we predicted that the SIOR effect would be larger when performing the task with an in-group member than with an out-group member. The results confirmed our prediction by indicating that the co-actor's group membership modulated the SIOR effect. These findings are consistent with the notion that social factors play a critical role in producing the SIOR effect and provide a novel indication of the influence of social factors such as group membership on basic reflexive cognitive processes.

How Task Interactivity Shapes Action Observation

Action observation triggers imitation, a powerful mechanism permitting interpersonal coordination. Coordination, however, also occurs when the partners’ actions are nonimitative and physically incongruent. One influential theory postulates that this is achieved via top-down modulation of imitation exerted by prefrontal regions. Here, we rather argue that coordination depends on sharing a goal with the interacting partner: this shapes action observation, overriding involuntary imitation, through the predictive activity of the left ventral premotor cortex (lvPMc). During functional magnetic resonance imaging (fMRI), participants played music in turn with a virtual partner in interactive and noninteractive conditions requiring 50% of imitative/nonimitative responses. In a full-factorial design, both perceptual features and low-level motor requirements were kept constant throughout the experiment. Behaviorally, the interactive context minimized visuomotor interference due to the involuntary imitation of physically incongruent movements. This was paralleled by modulation of neural activity in the lvPMc, which was specifically recruited during the interactive task independently of the imitative/nonimitative nature of the social exchange. This lvPMc activity reflected the predictive decoding of the partner’s actions, as revealed by multivariate pattern analysis. This demonstrates that, during interactions, we process our partners’ behavior to prospectively infer their contribution to the shared goal achievement, generating motor predictions for cooperation beyond low-level imitation.