The performance monitoring system is attuned to others' actions during dyadic motor interactions.

Interpersonal motor interactions require the simultaneous monitoring of one's own and one's partner's actions. To characterize how the action monitoring system tracks self and other behavior during synchronous interactions, we combined electroencephalography recordings and immersive virtual reality in two tasks where participants were asked to synchronize their actions with those of a virtual partner (VP). The two tasks differed in the features to be monitored: the Goal task required participants to predict and monitor the VP's reaching goal; the Spatial task required participants to predict and monitor the VP's reaching trajectory. In both tasks, the VP performed unexpected movement changes to which the participant needed to adapt. By extracting the neural activity locked to the detection of unexpected changes in the VP's action (other-monitoring) or to the participants' action-replanning (self-monitoring), we show that the monitoring system is more attuned to others' than to one's own actions. Additionally, distinctive neural responses to VP's unexpected goals and trajectory corrections were found: goal changes were reflected both in early fronto-central and later posterior neural responses while trajectory deviations were reflected only in later posterior responses. Altogether, our results indicate that the monitoring system adopts an inherent social mode to handle interpersonal motor interactions.

The social roots of self development: from a bodily to an intellectual interpersonal dialogue.

In this paper, we propose that interpersonal bodily interactions represent a fertile ground in which the bodily and psychological self is developed, gradually allowing for forms of more abstract and disembodied interactions. We start by focusing on how early infant-caregiver bodily interactions play a crucial role in shaping the boundaries of the self but also in learning to predict others' behavior. We then explore the social function of the sense of touch in the entire life span, highlighting its role in promoting physical and psychological well-being by supporting positive interpersonal exchanges. We go on by introducing the concept of implicit theory of mind, as the early ability to interpret others' intentions, possibly grounded in infant-caregiver bodily exchanges (embodied practices). In the following part, we consider so-called higher level forms of social interaction: intellectual exchanges among individuals. In this regard, we defend the view that, beside the apparent private dimension of "thinking abstractly", using abstract concepts is intrinsically a social process, as it entails the re-enactment of the internalized dialogue through which we acquired the concepts in the first place. Finally, we describe how the hypothesis of "dialectical attunement" may explain the development of abstract thinking: to effectively transform the world according to their survival needs, individuals co-construct structured concepts of it; by doing so, humans fundamentally transform not merely the world they are being in, but their being in the world.

Midfrontal Theta Transcranial Alternating Current Stimulation Facilitates Motor Coordination in Dyadic Human-Avatar Interactions.

Synchronous interpersonal motor interactions require moment-to-moment prediction and proactive monitoring of the partner's actions. Neurophysiologically, this is highlighted by an enhancement of midfrontal theta (4-7 Hz) oscillations. In this study, we explored the causal role of midfrontal theta for interpersonal motor interactions using transcranial alternating current stimulation (tACS). We implemented a realistic human-avatar interaction task in immersive virtual reality where participants controlled a virtual arm and hand to press a button synchronously with a virtual partner. Participants completed the task while receiving EEG-informed theta (Experiment 1) or beta (control frequency, Experiment 2) tACS over the frontal midline, as well as sham stimulation as a control. Results showed that midfrontal theta tACS significantly improved behavioral performance (i.e., reduced interpersonal asynchrony) and participants' motor strategies (i.e., increased movement times and reduced RTs), whereas beta tACS had no effect on these measures. These results suggest that theta tACS over frontal areas facilitates action monitoring and motor abilities supporting interpersonal interactions.

Inhibitory Theta Burst Stimulation Highlights the Role of Left aIPS and Right TPJ during Complementary and Imitative Human-Avatar Interactions in Cooperative and Competitive Scenarios.

Competitive and cooperative interactions are based on anticipation or synchronization with the partner's actions. Both forms of interaction may either require performing imitative or complementary movements with respect to those performed by our partner. We explored how parietal regions involved in the control of imitative behavior (temporo-parietal junction, TPJ), goal coding and visuo-motor integration (anterior intraparietal sulcus, aIPS) contribute to the execution of imitative and complementary movements during cooperative and competitive interactions. To this aim, we delivered off-line non-invasive inhibitory brain stimulation to healthy individuals' left aIPS and right TPJ before they were asked to reach and grasp an object together with a virtual partner by either performing imitative or complementary interactions. In different blocks, participants were asked to compete or cooperate with the virtual partner that varied its behavior according to cooperative or competitive contexts. Left aIPS and right TPJ inhibition impaired individuals' performance (i.e., synchrony in cooperative task and anticipation in competition) during complementary and imitative interactions, respectively, in both cooperative and competitive contexts, indicating that aIPS and TPJ inhibition affects own-other action integration and action imitation (that are different in complementary vs imitative interactions) more than action synchronization or anticipation (that are different in cooperative vs competitive contexts).

It's a matter of (executive) load: Separation as a load-dependent resetting procedure.

Lee and Schwarz made considerable theoretical advances in the psychology of cleansing by proposing that cleaning actions might serve as separation procedures between two psychological entities. Here, we propose that the effectiveness of the separation process may be modulated by the available amount of executive resources, and that separation may operate as a load-dependent resetting procedure.

Role of the occipito-temporal theta rhythm in hand visual identification.

Neuroimaging and EEG studies have shown that passive observation of the full body and of specific body parts is associated with 1) activity of an occipito-temporal region named the extrastriate body area (EBA), 2) amplitude modulations of a specific posterior event-related potential (ERP) component (N1/N190), and 3) a theta-band (4-7 Hz) synchronization recorded from occipito-temporal electrodes compatible with the location of EBA. To characterize the functional role of the occipito-temporal theta-band increase during the processing of body-part stimuli, we recorded EEG from healthy participants while they were engaged in an identification task (match-to-sample) of images of hands and nonbody control images (leaves). In addition to confirming that occipito-temporal electrodes show a larger N1 for hand images compared with control stimuli, cluster-based analysis revealed an occipito-temporal cluster showing an increased theta power when hands are presented (compared with leaves) and show that this theta increase is higher for identified hands compared with nonidentified ones while not being significantly different between not identified nonhand stimuli. Finally, single trial multivariate pattern analysis revealed that time-frequency modulation in the theta band is a better marker for classifying the identification of hand images than the ERP modulation. The present results support the notion that theta activity over the occipito-temporal cortex is an informative marker of hand visual processing and may reflect the activity of a network coding for stimulus identity.NEW & NOTEWORTHY Hands provide crucial information regarding the identity of others, which is a key information for social processes. We recorded EEG activity of healthy participants during the visual identification of hand images. The combination of univariate and multivariate pattern analysis in time- and time-frequency domain highlights the functional role of theta (4-7 Hz) activity over visual areas during hand identification and emphasizes the robustness of this neuromarker in occipito-temporal visual processing dynamics.

Modulation of preference for abstract stimuli following competence-based social status primes.

In the present study, we measured whether competence-related high and low social status attributed to two unknown individuals affects participants' implicit reactivity to abstract stimuli associated to the identity of the same individuals. During a status-inducing procedure, participants were asked to play an interactive game with two (fake) players coded as high vs low status based on their game competence. Before and after the game, a modified version of the Affective Misattribution Procedure (AMP) was administered in which the players' faces were used as primes. The evaluation target, as is typical to AMP, was a Chinese ideogram. There were two different presentation timings for the prime image: 75 ms and 17 ms. After the status-inducing procedure, the evaluation targets preceded by the high-status prime (i.e. best player's face) were rated as more pleasant than those preceded by the low-status prime (i.e. worst player's face). This effect was only found, however, for the 75 ms lasting prime. Moreover, explicit ratings of the primes showed that the high-status player was rated as more intelligent, competent and dominant than the low status one. These results indicate that implicit preference and explicit evaluation of unacquainted individuals are rapidly modulated by competence-based social status attribution, thus hinting at the plastic nature of social categorization and, relatedly, the malleability of visual preference.

Visuo-motor interference with a virtual partner is equally present in cooperative and competitive interactions.

Automatic imitation of observed actions is thought to be a powerful mechanism, one that may mediate the reward value of interpersonal interactions, but that could also generate visuo-motor interference when interactions involve complementary movements. Since interpersonal coordination seems to be crucial both when cooperating and competing with others, the questions arises as to whether imitation-and thus visuo-motor interference-occurs in both scenarios. To address this issue, we asked human participants to engage in high- or low-interactive (Interactive or Cued condition, respectively), cooperative or competitive, joint reach-to-grasps with a virtual partner. More specifically, interactions occurred in: (i) a Cued condition, where participants simply adapted their movement timing to synchronize with (during cooperation) or anticipate (during competition) the virtual partner's grasp; (ii) an Interactive condition requiring the same adaptation, as well as a real-time selection of their action according to the virtual character's movement. To simulate a realistic human-human interaction, the virtual character would change its movement speed in consecutive trials according to participants' behaviour. Results demonstrate that visuo-motor interference-as indexed by movement kinematics (higher maximum wrist height during complementary compared to imitative power grips)-emerge in both cooperative and competitive motor interactions only when predictions about the partner's movements are needed to perform one's own action (interactive condition). These results support the idea that simulative imitation is heavily present when individuals need to match their behaviours closely.

Subliminal presentation of emotionally negative vs positive primes increases the perceived beauty of target stimuli.

Emotions have a profound influence on aesthetic experiences. Studies using affective priming procedures demonstrate, for example, that inducing a conscious negative emotional state biases the perception of abstract stimuli towards the sublime (Eskine et al. Emotion 12:1071-1074, 2012. doi: 10.1037/a0027200). Moreover, subliminal happy facial expressions have a positive impact on the aesthetic evaluation of abstract art (Flexas et al. PLoS ONE 8:e80154, 2013). Little is known about how emotion influences aesthetic perception of non-abstract, representational stimuli, especially those that are particularly relevant for social behaviour, like human bodies. Here, we explore whether the subliminal presentation of emotionally charged visual primes modulates the explicit subjective aesthetic judgment of body images. Using a forward/backward masking procedure, we presented subliminally positive and negative, arousal-matched, emotional or neutral primes and measured their effect on the explicit evaluation of perceived beauty (high vs low) and emotion (positive vs negative) evoked by abstract and body images. We found that negative primes increased subjective aesthetic evaluations of target bodies or abstract images in comparison with positive primes. No influence of primes on the emotional dimension of the targets was found, thus ruling out an unspecific arousal effect and strengthening the link between emotional valence and aesthetic appreciation. More specifically, that subliminal negative primes increase beauty ratings compared to subliminal positive primes indicates a clear link between negative emotions and positive aesthetic evaluations and vice versa, suggesting a possible link between negative emotion and the experience of sublime in art. The study expands previous research by showing the effect of subliminal negative emotions on the subjective aesthetic evaluation not only of abstract but also of body images.

The dopaminergic system supports flexible and rewarding dyadic motor interactive behaviour in Parkinson's Disease.

Studies indicate that the dopaminergic system (DAS) supports individual flexible behaviour. While flexibility is quintessential to effective dyadic motor interactions, whether DAS mediates adaptations of one's own motor behaviour to that of a partner is not known. Here, we asked patients with Parkinson's Disease (PD) to synchronize their grasping movements with those of a virtual partner in conditions that did (Interactive) or did not (Cued) require to predict and adapt to its actions. PD performed the task during daily antiparkinsonian treatment ('On' condition) or after drug-withdrawal ('Off' condition). A group of healthy individuals also served as control group. In the Interactive condition, PDs performed better and found the interaction more enjoyable when in 'On' than in 'Off' condition. Crucially, PD performance in the 'On' condition did not differ from that of healthy controls. This pattern of results hints at the key role of the DAS in supporting the flexible adaptation of one's own actions to the partner's during motor interactions.

Interpersonal Motor Interactions Shape Multisensory Representations of the Peripersonal Space.

This perspective review focuses on the proposal that predictive multisensory integration occurring in one's peripersonal space (PPS) supports individuals' ability to efficiently interact with others, and that integrating sensorimotor signals from the interacting partners leads to the emergence of a shared representation of the PPS. To support this proposal, we first introduce the features of body and PPS representations that are relevant for interpersonal motor interactions. Then, we highlight the role of action planning and execution on the dynamic expansion of the PPS. We continue by presenting evidence of PPS modulations after tool use and review studies suggesting that PPS expansions may be accounted for by Bayesian sensory filtering through predictive coding. In the central section, we describe how this conceptual framework can be used to explain the mechanisms through which the PPS may be modulated by the actions of our interaction partner, in order to facilitate interpersonal coordination. Last, we discuss how this proposal may support recent evidence concerning PPS rigidity in Autism Spectrum Disorder (ASD) and its possible relationship with ASD individuals' difficulties during interpersonal coordination. Future studies will need to clarify the mechanisms and neural underpinning of these dynamic, interpersonal modulations of the PPS.

Competence-based social status and implicit preference modulate the ability to coordinate during a joint grasping task.

Studies indicate that social status influences people's social perceptions. Less information is available about whether induced social status influences dyadic coordination during motor interactions. To explore this issue, we designed a study in which two confederates obtained high or low competence-based status by playing a game together with the participant, while the participant always occupied the middle position of the hierarchy. Following this status-inducing phase, participants were engaged in a joint grasping task with the high- and low-status confederates in different sessions while behavioural (i.e., interpersonal asynchrony and movement start time) indexes were measured. Participants' performance in the task (i.e., level of interpersonal asynchrony) when interacting with the low-status partner was modulated by their preference for him. The lower participants' preference for a low- relative to a high-status confederate, the worse participants' performance when interacting with the low-status confederate. Our results show that participants' performance during motor interactions changes according to the social status of the interaction partner.

Dissociating cognitive, behavioral and physiological stress-related responses through dorsolateral prefrontal cortex inhibition.

The left dorsolateral prefrontal cortex (dlPFC) has been implicated in the regulation of stress-related cognitive processes and physiological responses and is the principal target of noninvasive brain stimulation techniques applied to psychiatric conditions. However, existing studies are mostly correlational and causal evidence on the role of this region in mediating specific psychophysiological mechanisms underpinning stress-related responses are needed to make the application of such techniques more efficient. To fill this gap, this study used inhibitory continuous theta burst stimulation (cTBS) in healthy individuals to examine the extent to which activity of the left dlPFC is associated with cognitive (subjective focus on a tracking task), behavioral (reaction times and variability), and physiological responses (heart rate and its variability and cortisol level) following induction of perseverative cognition. Compared to sham and left ventral PreMotor area stimulation (as active control area), inhibition of left dlPFC determined sustained autonomic and neuroendocrine activation and increased the subjective perception of being task-focused, while not changing the behavioral and self-reported stress-related responses. Adopting a causative approach, we describe a role of left dlPFC in inhibitory control of the physiological stress-response associated to perseverative thinking.

Abstract concepts in interaction: the need of others when guessing abstract concepts smooths dyadic motor interactions.

concepts (ACs, e.g. 'justice') are more complex compared with concrete concepts (CCs) (e.g. 'table'). Indeed, they do not possess a single object as a referent, they assemble quite heterogeneous members and they are more detached from exteroceptive and more grounded in interoceptive experience. Recent views have hypothesized that interpersonal communication is particularly crucial to acquire and use ACs. The current study investigates the reliance of ACs/CCs representation on interpersonal behaviour. We asked participants to perform a motor interaction task with two avatars who embodied two real confederates. Before and after the motor interaction task, the two confederates provided participants with hints in a concept guessing task associated with visual stimuli: one helped in guessing ACs and the other, CCs. A control study we performed both with the materials employed in the main experiment and with other materials, confirmed that associating verbal concepts with visual images was more difficult with ACs than with CCs. Consistently, the results of the main experiment showed that participants asked for more hints with ACs than CCs and were more synchronous when interacting with the avatar corresponding to the AC's confederate. The results highlight an important role of sociality in grounding ACs.

Midline frontal and occipito-temporal activity during error monitoring in dyadic motor interactions.

Discrepancies between sensory predictions and action outcome are at the base of error coding. However, these phenomena have mainly been studied focussing on individual performance. Here, we explored EEG responses to motor prediction errors during a human-avatar interaction and show that Theta/Alpha activity of the frontal error-monitoring system works in phase with activity of the occipito-temporal node of the action observation network. Our motor interaction paradigm required healthy individuals to synchronize their reach-to-grasp movements with those of a virtual partner in conditions that did (Interactive) or did not require (Cued) movement prediction and adaptation to the partner's actions. Crucially, in 30% of the trials the virtual partner suddenly and unpredictably changed its movement trajectory thereby violating the human participant's expectation. These changes elicited error-related neuromarkers (ERN/Pe - Theta/Alpha modulations) over fronto-central electrodes during the Interactive condition. Source localization and connectivity analyses showed that the frontal Theta/Alpha activity induced by violations of the expected interactive movements was in phase with occipito-temporal Theta/Alpha activity. These results expand current knowledge about the neural correlates of on-line interpersonal motor interactions linking the frontal error-monitoring system to visual, body motion-related, responses.

Contextual and social variables modulate aesthetic appreciation of bodily and abstract art stimuli.

Despite the increasing interest in the plasticity of aesthetic appreciation, we know comparatively little about the role of individuals' cultural (e.g. the appreciators' expertise) and of social emotional-cognitive (e.g. the social influence of people perceived as warm or competent) variables in modulating the appreciation process. In two experiments we investigated 1) whether people with different art-expertise are influenced differently by contextual (i.e. stimuli primed as art) and social (i.e. stimuli rated as beautiful by art-critics) information and 2) whether acknowledging the judgment of a person perceived as warm or as competent has a different influence on individuals' aesthetic appreciation of art works. Warmth and competence are two social dimensions of fundamental importance for categorizing others as in-group or out-group (Fiske, Cuddy, Glick, & Xu, 2002). We found that insinuating that the observed works were pieces of art, highly appreciated by art critics, lead expert participants to judge the stimuli as more beautiful in comparison to when the very same stimuli were not preceded by any manipulation. Moreover, we found that both art-experts and non-experts rated the stimuli as more beautiful when they believed it to be highly appreciated by people perceived as warm vs people perceived as competent. These results provide novel information on the plasticity of aesthetics and pave the way to understanding how tastes and preferences in the domain of aesthetics can be influenced.

Interactor's body shape does not affect visuo-motor interference effects during motor coordination.

The biological-tuning of the Action Observation Network is highly debated. A current open question relates to whether the morphological appearance (body shape) and/or the biological motion of the observed agent triggers action simulation processes. Motor simulation of the partner's action is critical for motor interactions, where two partners coordinate their actions in space and time. It supports interpersonal alignment and facilitates online coordination. However, motor simulation also leads to visuo-motor interference effects when people are required to coordinate with complementary actions, i.e. incongruent movements as compared to the observed ones. Movement kinematics of interactive partners allows us to capture their automatic tendency to simulate and imitate the partner's complementary movements. In an online reach-to-grasp task, we investigated whether visuo-motor interference effects, visible in the kinematics of complementary movements, are modulated by the visual presence of the interactor's body shape. We asked participants to interact with 1) a humanoid agent with a human-like body shape and with real human, biological, movement kinematics, or 2) a non-humanoid agent, which did not resemble the human body-shape but moved with the same real kinematics. Through the combination of inferential and Bayesian statistics, the results show no effect of interactor's body shape on visuo-motor interference in reaching and grasping kinematics during online motor coordination. We discuss the results and propose that the kinematics of the observed movements, during motor interactions, might be the key factor for visuo-motor interference to take place independently from the morphological appearance of the partner. This is particularly relevant in a technological society that constantly asks humans to interact with artificial agents.

Inhibition of left anterior intraparietal sulcus shows that mutual adjustment marks dyadic joint-actions in humans.

Creating real-life dynamic contexts to study interactive behaviors is a fundamental challenge for the social neuroscience of interpersonal relations. Real synchronic interpersonal motor interactions involve online, inter-individual mutual adaptation (the ability to adapt one's movements to those of another in order to achieve a shared goal). In order to study the contribution of the left anterior Intra Parietal Sulcus (aIPS) (i.e. a region supporting motor functions) to mutual adaptation, here, we combined a behavioral grasping task where pairs of participants synchronized their actions when performing mutually adaptive imitative and complementary movements, with the inhibition of activity of aIPS via non-invasive brain stimulation. This approach allowed us to investigate whether aIPS supports online complementary and imitative interactions. Behavioral results showed that inhibition of aIPS selectively impairs pair performance during complementary compared to imitative interactions. Notably, this effect depended on pairs' mutual adaptation skills and was higher for pairs composed of participants who were less capable of adapting to each other. Thus, we provide the first causative evidence for a role of the left aIPS in supporting mutually adaptive interactions and show that the inhibition of the neural resources of one individual of a pair is compensated at the dyadic level.

Come together: human-avatar on-line interactions boost joint-action performance in apraxic patients.

Limb apraxia (LA) is a high-order motor disorder linked to left-hemisphere damage. It is characterized by defective execution of purposeful actions upon delayed imitation, or verbal command when the actions are performed in isolated, non-naturalistic, conditions. Whether interpersonal interactions provide social affordances that activate neural resources different from those requested by individual action execution, which may improve LA performance, is unknown. To fill this gap, we measured interaction performance, behavioral and kinematic indexes of left-brain damaged patients with/without LA in a social reach-to-grasp task involving two different degrees of spatio-temporal interactivity with an avatar. We found that LA patients' impairment in coordinating with the virtual partner was abolished in highly interactive conditions (where patients selected their actions on-line based on the behavior of the virtual partner) with respect to low interactive conditions (where actions were selected beforehand based on abstract instructions). Voxel-based-Lesion-Symptom-Mapping indicated that impairments in low-interactive conditions were underpinned by lesions of premotor, motor and insular areas, and of the basal ganglia. Our approach expands current understanding of the behavioral and neural correlates of interactive motor performance by highlighting the important role of social affordances, and provides novel, potentially important, views on rehabilitation of higher-order motor cognition disorders.