For your eyes only: effect of confederate's eye level on reach-to-grasp action

Sex of an Observer Effects on Adults' Motor, Cognitive, and Affective Dart-Shooting Performance

Men and women are characterized by specific physiological, cerebral and emotional characteristics, as well as by the differing nature of their gestures and behaviors. Here, we examined the effects of an observer's sex on motor, cognitive and affective behaviors during dart-shooting. We compared men and women's kinematic and affective parameters when perfoming alone or when performing in the presence of an observer of a different sex. We found a sex effect on motor and cognitive performance in interaction with participants' emotional states. We observed improved accuracy and reaction time in men compared to women, which we attributed to (a) differences in emotional sensitivities between the two sexes and (b) men's superiority on precision tasks linked to men's higher proportion of cerebral white matter. Our findings also suggested a sex difference in the social effect of an observer's sex on motor and cognitive performance. Although there was no effect on affective aspects of performance, emotional state seemed to interact strongly with this social effect.

The contribution of eye gaze and movement kinematics to the expression and identification of social intention in object-directed motor actions

The intention to include another person in an interaction (i.e., social intention) is known to influence the spatio-temporal characteristics of motor performances. However, the interplay between these kinematic variations and the social cues provided by eye gaze has not been properly assessed yet. In the present study, we tested whether limiting the access to eye gaze altered the motor-related effects of social intention on motor performances. In a dyadic interaction, the agents' task was to displace a dummy glass to a new position with the intention to fill it themselves (personal intention) or having it filled by the observers facing them (social intention). The observers performed their action only when they were able to identify a social intention in agents' action. The task was performed while having access to observers' eye gaze or not, through the manipulation of an occluder. Results showed an effect of social intention on agents' motor performances, that induced an amplification of the kinematic spatio-temporal parameters. Such amplification was smaller when the observers' eye gaze was not available. In this latter condition, the identification of the social intention in the observed actions was impaired. Altogether, the results suggest that the presence of eye gaze cues contributes significantly to the success of social interaction, by facilitating the expression and the understanding of social intentions through the kinematics of object-directed actions.

Humanoid facial expressions as a tool to study human behaviour

Besides action vitality forms, facial expressions represent another fundamental social cue which enables to infer the affective state of others. In the present study, we proposed the iCub robot as an interactive and controllable agent to investigate whether and how different facial expressions, associated to different action vitality forms, could modulate the motor behaviour of participants. To this purpose, we carried out a kinematic experiment in which 18 healthy participants observed video-clips of the iCub robot performing a rude or gentle request with a happy or angry facial expression. After this request, they were asked to grasp an object and pass it towards the iCub robot. Results showed that the iCub facial expressions significantly modulated participants motor response. Particularly, the observation of a happy facial expression, associated to a rude action, decreased specific kinematic parameters such as velocity, acceleration and maximum height of movement. In contrast, the observation of an angry facial expression, associated to a gentle action, increased the same kinematic parameters. Moreover, a behavioural study corroborated these findings, showing that the perception of the same action vitality form was modified when associated to a positive or negative facial expression.

The social cognitive dimension of pantomime

Pantomime production is commonly interpreted as reflecting tool-use-related cognitive processes. Yet, in everyday life, pantomime deserves a communication function and the exaggeration of amplitude found during pantomime compared to real tool use may reflect the individual's attempt to communicate the intended gesture. Therefore, the question arises about whether pantomime is a communicative behavior that is nevertheless supported only by non-social cognitive processes. We contribute to answering this question by using kinematic analyses. Participants performed the pantomime of using a saw or a hammer from visual presentation in three conditions: Free (no specific instructions), Self (focus on the real tool-use action), and Others (focus on the communicative dimension). Finally, they used the tool with the corresponding object (Actual condition). Participants' social cognition were assessed using gold standard questionnaires. Our results indicated that the manipulation of instructions had a minor effect on the exaggeration of amplitude during pantomime. We reported a link between the social cognition score and the amplitude in the Others condition for the hammer, which suggests that social cognitive processes could take part in pantomime production in some conditions. Nevertheless, this result does not alter our conclusion that social cognitive processes might be far from necessary for pantomime production.

Effect of Social Context on Cognitive and Motor Behavior: A Systematic Review

Human cognitive and motor behavior is influenced by the social contexts. The aim of this systematic review is to investigate the impact of the social contexts on human behaviors. A systematic search of the literature was performed via Pub-Med/Medline, Web of sciences, Google scholar, Science direct, Springer-Link and EMBASE and 68 articles were selected. After applying all the inclusion and exclusion criteria, 16 articles were retained. The results show that the presence of other people and the social context influence motor behavior (i.e. movement duration, trajectory behavior, maximum speed) and cognitive behavior (reaction time). Studies have shown an improvement in performance in the presence of other people compared to the individual situation. However, other studies showed that the presence of other people led to deterioration in performance compared to the individual situation. The improvement of behavior is attributed to the social phenomenon of facilitation while the deterioration was explained by the conduct theory or the distraction conflict theory. These social phenomena of facilitation or inhibition could be related to the perception-action theory, which interferes with interaction with other. This, in turn, seems to be associated with neural circuits of mirror neurons and motor system.

The influence of cooperative action intention on object affordance: evidence from the perspective-taking ability of individuals

In complex interactive scenarios, action understanding lies at the heart of social interactions. Nevertheless, the ability to understand action intention may differ among people. The current study distinguished two groups of participants with different social intention-understanding abilities (high and low) based on a perspective-taking task to investigate the influence of social intention on object affordance under conditions of individual and cooperative action intention. In the affordance perception experiment, participants were shown a video with the presenter reaching to grasp an object in different grips and asked to classify objects into kitchen or non-kitchen items by pressing the left- or right-hand button under the two intention conditions. The results showed that the object affordance effects were modulated by the participants' understanding of social intention in the interactive scenarios. Specifically, the object affordance effects were observed only in the high perspective-taking ability group under the condition of cooperative action intention. However, under the condition of individual action intention, object affordance effects were shown in both the high and low perspective-taking ability groups, and the difference between the two groups was not significant. This study suggests that processing of object affordance depends greatly on the contextual correspondence of perception and action and that the understanding of cooperative action intention can affect the activation of object affordance.

The ability to predict actions of others from distributed cues is still developing in 6- to 8-year-old children

Adults use distributed cues in the bodies of others to predict and counter their actions. To investigate the development of this ability, we had adults and 6- to 8-year-old children play a competitive game with a confederate who reached toward one of two targets. Child and adult participants, who sat across from the confederate, attempted to beat the confederate to the target by touching it before the confederate did. Adults used cues distributed through the head, shoulders, torso, and arms to predict the reaching actions. Children, in contrast, used cues in the arms and torso, but we did not find any evidence that they could use cues in the head or shoulders to predict the actions. These results provide evidence for a change in the ability to respond rapidly to predictive cues to others’ actions from childhood to adulthood. Despite humans’ sensitivity to action goals even in infancy, the ability to read cues from the body for action prediction in rapid interactive settings is still developing in children as old as 6 to 8 years of age.

Subtle predictive movements reveal actions regardless of social context

Humans have a remarkable ability to predict the actions of others. To address what information enables this prediction and how the information is modulated by social context, we used videos collected during an interactive reaching game. Two participants (an “initiator” and a “responder”) sat on either side of a plexiglass screen on which two targets were affixed. The initiator was directed to tap one of the two targets, and the responder had to either beat the initiator to the target (competition) or arrive at the same time (cooperation). In a psychophysics experiment, new observers predicted the direction of the initiators' reach from brief clips, which were clipped relative to when the initiator began reaching. A machine learning classifier performed the same task. Both humans and the classifier were able to determine the direction of movement before the finger lift-off in both social conditions. Further, using an information mapping technique, the relevant information was found to be distributed throughout the body of the initiator in both social conditions. Our results indicate that we reveal our intentions during cooperation, in which communicating the future course of actions is beneficial, and also during competition despite the social motivation to reveal less information.

Pupils say more than a thousand words: Pupil size reflects how observed actions are interpreted

Humans attend to others' facial expressions and body language to better understand their emotions and predict goals and intentions. The eyes and its pupils reveal important social information. Because pupil size is beyond voluntary control yet reflective of a range of cognitive and affective processes, pupils in principal have the potential to convey whether others' actions are interpreted correctly or not. Here, we measured pupil size while participants observed video-clips showing reach-to-grasp arm movements. Expressors in the video-clips were playing a board game and moved a dowel to a new position. Participants' task was to decide whether the dowel was repositioned with the intention to be followed up by another move of the same expressor (personal intention) or whether the arm movement carried the implicit message that expressor's turn was over (social intention). Replicating earlier findings, results showed that participants recognized expressors' intentions on the basis of their arm kinematics. Results further showed that participants' pupil size was larger when observing actions reflecting personal compared to social intentions. Most interestingly, before participants indicated how they interpreted the observed actions by choosing to press one of two keys (corresponding to the personal or social intention), their pupils within a split second, had already given away how they interpreted the expressor's movement. In sum, this study underscores the importance of nonverbal behavior in helping social messages get across quickly. Revealing how actions are interpreted, pupils may provide additional feedback for effective social interactions.

Multiple Frames of Reference Are Used During the Selection and Planning of a Sequential Joint Action

Co-actors need to anticipate each other's actions to successfully perform joint actions. The frames of reference (FOR) used to simulate a co-actor's action could impact what information is anticipated. We hypothesized that co-actor's would adopt their co-actor's body-centered FOR, even when they do not share the same spatial orientation, so that they could anticipate body-related aspects of their co-actor's task. Because it might be beneficial to plan joint actions based on environment and body-centered information, we hypothesized that individuals would utilize multiple FORs during response planning. To test these hypotheses, participants performed a sequential aiming task where the goal was to move a wooden dowel to one of four potential targets as quickly and accurately as possible. A cue was presented at the beginning of each trial that was either 25, 50, or 75% valid. Following the cue presentation, the first person to act (initiator) placed the wooden dowel, anywhere they liked, in the workspace. Then, the finisher performed their aiming movement from the location that the initiator had placed the dowel. The key dependent measure was the dowel placement of the initiator because it provided an index of how much the initiator attempted to facilitate the efficient performance of the finisher. The results revealed that individuals adopted an allocentric FOR (dowel placement was more biased toward cued locations as cue validity increased) and partially adopted their co-actor's body-centered FOR (dowel placement was biased toward the finisher's body, but not toward the co-actor's contralateral space). In conclusion, multiple FORs can be used to anticipate both body- and environment-related information of a co-actor's task. It may be difficult, however, for individuals to fully adopt their co-actor's body-centered FOR when they have differing orientations.

Cooperative and competitive contexts do not modify the effect of social intention on motor action

In social interactions, the movements performed by others can be used to anticipate their intention. The present paper investigates whether cooperative vs competitive contexts influence the kinematics of object-directed motor actions and whether they modulate the effect of social intention on motor actions. An "Actor" and a "Partner" participated in a task consisting in displacing a wooden dowel under time constraint. Before this Main action, the Actor performed a Preparatory action which consisted in placing the dowel at the center of the table. Information about who would make the forthcoming Main action was provided only to the Actor through headphones. Results demonstrate an exaggeration of spatial and temporal actions' parameters when acting for the Partner, in cooperative, as well as in competitive context. This finding suggests that the motor manifestation of social intention is largely determined by non-conscious implicit processes that seem little influenced by the context of social interaction.

Communicative knowledge pervasively influences sensorimotor computations

Referential pointing is a characteristically human behavior, which involves moving a finger through space to direct an addressee towards a desired mental state. Planning this type of action requires an interface between sensorimotor and conceptual abilities. A simple interface could supplement spatially-guided motor routines with communicative-ostensive cues. For instance, a pointing finger held still for an extended period of time could aid the addressee’s understanding, without altering the movement’s trajectory. A more complex interface would entail communicative knowledge penetrating the sensorimotor system and directly affecting pointing trajectories. We compare these two possibilities using motion analyses of referential pointing during multi-agent interactions. We observed that communicators produced ostensive cues that were sensitive to the communicative context. Crucially, we also observed pervasive adaptations to the pointing trajectories: they were tailored to the communicative context and to partner-specific information. These findings indicate that human referential pointing is planned and controlled on the basis of partner-specific knowledge, over and above the tagging of motor routines with ostensive cues.

The role of perspective in discriminating between social and non-social intentions from reach-to-grasp kinematics

Making correct inferences regarding social and individual intentions may be crucial for successful interactions, especially when we are required to discriminate between cooperative and competitive behaviors. The results of previous studies indicate that reach-to-grasp kinematic parameters may be used to infer the social or individual outcome of a movement. However, the majority of the studies investigated this ability by presenting reach-to-grasp movements from a third-person perspective only. The aim of the present study was to assess whether the ability to recognize the intent associated to a reach-to-grasp movement varies as a function of perspective by manipulating the perspective of observation (second- and third-perspective) within participants. To this end, we presented participants with video clips of models performing a reach-to-grasp movement with different intents. The video clips were recorded both from a lateral view (third-person perspective) and from a frontal view (second-person perspective). After viewing the clips, in two subsequent tasks participants were asked to distinguish between social and non-social intentions by observing the initial phase of the same action recorded from the two different views. Results showed that, when a fast-speed movement was presented from a lateral view, participants were able to predict its social intention. In contrast, when the same movement was observed from a frontal view, performance was impaired. These results indicate that the ability to detect social intentions from motor cues can be biased by the visual perspective of the observer, specifically for fast-speed movements.

Facilitation effect of observed motor deviants in a cooperative motor task: Evidence for direct perception of social intention in action

Spatiotemporal parameters of voluntary motor action may help optimize human social interactions. Yet it is unknown whether individuals performing a cooperative task spontaneously perceive subtly informative social cues emerging through voluntary actions. In the present study, an auditory cue was provided through headphones to an actor and a partner who faced each other. Depending on the pitch of the auditory cue, either the actor or the partner were required to grasp and move a wooden dowel under time constraints from a central to a lateral position. Before this main action, the actor performed a preparatory action under no time constraint, consisting in placing the wooden dowel on the central location when receiving either a neutral ("prêt"-ready) or an informative auditory cue relative to who will be asked to perform the main action (the actor: "moi"-me, or the partner: "lui"-him). Although the task focused on the main action, analysis of motor performances revealed that actors performed the preparatory action with longer reaction times and higher trajectories when informed that the partner would be performing the main action. In this same condition, partners executed the main actions with shorter reaction times and lower velocities, despite having received no previous informative cues. These results demonstrate that the mere observation of socially driven motor actions spontaneously influences the low-level kinematics of voluntary motor actions performed by the observer during a cooperative motor task. These findings indicate that social intention can be anticipated from the mere observation of action patterns.

Individual differences in reading social intentions from motor deviants

As social animals, it is crucial to understand others’ intention. But is it possible to detect social intention in two actions that have the exact same motor goal? In the present study, we presented participants with video clips of an individual reaching for and grasping an object to either use it (personal trial) or to give his partner the opportunity to use it (social trial). In Experiment 1, the ability of naïve participants to classify correctly social trials through simple observation of short video clips was tested. In addition, detection levels were analyzed as a function of individual scores in psychological questionnaires of motor imagery, visual imagery, and social cognition. Results revealed that the between-participant heterogeneity in the ability to distinguish social from personal actions was predicted by the social skill abilities. A second experiment was then conducted to assess what predictive mechanism could contribute to the detection of social intention. Video clips were sliced and normalized to control for either the reaction times (RTs) or/and the movement times (MTs) of the grasping action. Tested in a second group of participants, results showed that the detection of social intention relies on the variation of both RT and MT that are implicitly perceived in the grasping action. The ability to use implicitly these motor deviants for action-outcome understanding would be the key to intuitive social interaction.

Perceiving what you intend to do from what you do: evidence for embodiment in social interactions

Although action and perception are central components of our interactions with the external world, the most recent experimental investigations also support their implications in the emotional, decision-making, and goal ascription processes in social context. In this article, we review the existing literature supporting this view and highlighting a link between reach-to-grasp motor actions and social communicative processes. First, we discuss the most recent experimental findings showing how the social context subtly influences the execution of object-oriented motor actions. Then, we show that the kinematic characteristics of object-oriented motor actions are modulated by the actor's social intention. Finally, we demonstrate that naïve observers can implicitly take advantage of these kinematic effects for their own motor productions. Considered together, these data are compatible with the embodied cognition framework stating that cognition, and in our case social cognition, is grounded in knowledge associated with past sensory and motor experiences.

Motor interference in interactive contexts

Action observation and execution share overlapping neural substrates, so that simultaneous activation by observation and execution modulates motor performance. Previous literature on simple prehension tasks has revealed that motor influence can be two-sided: facilitation for observed and performed congruent actions and interference for incongruent actions. But little is known of the specific modulations of motor performance in complex forms of interaction. Is it possible that the very same observed movement can lead either to interference or facilitation effects on a temporally overlapping congruent executed action, depending on the context? To answer this question participants were asked to perform a reach-to-grasp movement adopting a precision grip (PG) while: (i) observing a fixation cross, (ii) observing an actor performing a PG with interactive purposes, (iii) observing an actor performing a PG without interactive purposes. In particular, in the interactive condition the actor was shown trying to pour some sugar on a large cup located out of her reach but close to the participant watching the video, thus eliciting in reaction a complementary whole-hand grasp. Notably, fine-grained kinematic analysis for this condition revealed a specific delay in the grasping and reaching components and an increased trajectory deviation despite the observed and executed movement’s congruency. Moreover, early peaks of trajectory deviation seem to indicate that socially relevant stimuli are acknowledged by the motor system very early. These data suggest that interactive contexts can determine a prompt modulation of stimulus–response compatibility effects.