Optimal control models of biological movements are used to account for those internal variables that constrain voluntary goal-directed actions. They, however, do not take into account external environmental constraints as those associated to social intention. We investigated here the effects of the social context on kinematic characteristics of sequential actions consisting in placing an object on an initial pad (preparatory action) before reaching and grasping as fast as possible the object to move it to another location (main action). Reach-to-grasp actions were performed either in an isolated condition or in the presence of a partner (audience effect), located in the near or far space (effect of shared reachable space), and who could intervene on the object in a systematic fashion (effect of social intention effect) or not (effect of social uncertainty). Results showed an absence of audience effect but nevertheless an influence of the social context both on the main and the preparatory actions. In particular, a “localized” effect of shared reachable space was observed on the main action, which was smoother when performed within the reachable space of the partner. Furthermore, a “global” effect of social uncertainty was observed on both actions with faster and jerkier movements. Finally, social intention affected the preparatory action with higher wrist displacements and slower movements when the object was placed for the partner rather than placed for self-use. Overall, these results demonstrate specific effects of action space, social uncertainty and social intention on the planning of reach-to-grasp actions, in particular on the preparatory action, which was performed with no specific execution constraint. These findings underline the importance of considering the social context in optimal models of action control for human–robot interactions, in particular when focusing on the implementation of motor parameters required to afford intuitive interactions.

The present study evaluates whether in schizophrenia deficits in specifying social distances appropriately for interindividual interactions might be related to abnormal capabilities in specifying the boundaries of reachable space. Using a stop-distance paradigm, 20 patients with schizophrenia and their controls judged from seven preselected angles when a target reached the boundaries of peripersonal space. Results revealed that spatial perception was similar for patients and controls throughout the workspace with more accurate judgments in the preferred hemi-field. Nevertheless, patients were significantly more variable in their judgments; this variability was correlated with the PANSS disorganization cluster. In task 2, participants were required to judge either the boundaries of reachable space (target was an object) or to evaluate social distances (target was a person). Results revealed here again increased judgment variability in schizophrenia, in both situations. Of key importance was that results were normalized in the patients, when judgments were made through voluntary movement. These results argue for a similar brain mechanism for the determination of space and social distances. Furthermore, they suggest an important role of voluntary movement for the creation of stronger motor representations of action goals, which provide the basis for more accurate judgments of space boundaries during both physical and social interactions. The findings are discussed in light of the embodied theory of cognition and their implications for social skills in patients suffering from mental illnesses.

Finger-tapping tasks are classically used to investigate sensorimotor synchronization in relation to neutral auditory cues, such as metronomes. However, music is more commonly associated with an entrained bodily response, such as toe tapping, or dancing. Here we report an experimental procedure that was designed to bridge the gap between timing and intervention studies by directly comparing the effects of metronome and musical cue types on motor timing abilities across the three naturalistic voluntary actions of finger tapping, toe tapping, and stepping on the spot as a simplified case of whole body movement. Both pacing cues were presented at slow, medium, and fast tempi. The findings suggested that the task of stepping on the spot enabled better timing performances than tapping both in younger and older adults (75+). Timing performances followed an inverse U shape with best performances observed in the medium tempi that were set close to the spontaneous motor tempo in each movement type. Finally, music provided an entrainment effect in addition to pace setting that enabled better motor timing and greater stability than classically reported using a metronome. By applying time-stamp analyses to kinetic data, we demonstrate that tapping and stepping engage different timing modes. This work details the importance of translational research for a better understanding of motor timing. It offers a simple procedure that strengthens the validity of applying academic work and contributes in knowledge towards a wide range of therapeutic interventions.

Motor imagery is defined as a dynamic state during which the representation of a given motor act is internally rehearsed without overt motor output. Some evidence in experimental psychology has suggested that imagery ability is crucial for the correct understanding of social intention. The present study was conducted first to confirm that the nature of the motor intention leads to early modulations of movement kinematics. Secondly, we tested whether humans use imagery to read an agent’s intention when observing the very first element of a complex action sequence. Results revealed early variations in movement kinematics between three different social actions and further showed that human agents can use these early deviants to anticipate above chance level the end-result before seeing the second half of the sequence. Response times in the observation task were similar in duration to those measured in the true production task, suggesting the use of motor imagery for trial categorization. Nevertheless, in a third study, the use of an artificial (neural network) classifier demonstrated that classification within the first 500 ms is possible without cognitive imagery processing. Hence, our results suggest that low-level motor indices afford intention reading without need for motor imagery but that human agents may use imaging beyond simulation to create an embodied sense of interactivity.

Moderate physical activity can be experienced by some as pleasurable and by others as discouraging. This may be why many people lack sufficient motivation to participate in the recommended 150 minutes of moderately intense exercise per week. In the present study, we assessed how pleasure and enjoyment were modulated differently by one’s tolerance to self-paced physical activity. Sixty-three healthy individuals were allocated to three independent experimental conditions: a resting condition (watching TV), a cycling in silence condition, and a cycling in music condition. The tolerance threshold was assessed using the PRETIE-Questionnaire. Physical activity consisted in cycling during 30 minutes, at an intensity perceived as “somewhat difficult” on the Ratings of Perceived Exertion Scale. While controlling for self-reported physical activity level, results revealed that for the same perception of exertion and a similar level of enjoyment, the High Tolerance group produced more power output than the Low Tolerance group. There was a positive effect of music for High Tolerant individuals only, with music inducing greater power output and more pleasure. There was an effect of music on heart rate frequency in the Low Tolerant individuals without benefits in power output or pleasure. Our results suggest that for Low Tolerant individuals, energizing environments can interfere with the promised (positive) distracting effects of music. Hence, tolerance to physical effort must be taken into account to conceive training sessions that seek to use distracting methods as means to sustain pleasurable exercising over time.