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Highlights • Observation of others’ actions provides a shared experience of objects acted upon. • Observation of grasping movements provides a shared experience of object weight. • Object weight can be predictively judged from the kinematics of real grasps. • Weight judgements are also possible from the observation of pantomimed grasps., Observation of others’ actions has been proposed to provide a shared experience of the properties of objects acted upon. We report results that suggest a similar form of shared experience may be gleaned from the observation of pantomimed grasps, i.e., grasps aimed at pretended objects. In a weight judgment task, participants were asked to observe a hand reaching towards and grasping either a real or imagined glass, and to predictively judge its weight. Results indicate that participants were able to discriminate whether the to-be-grasped glass was empty, and thus light, or full, and thus heavy. Worthy of further investigation, this finding suggests that by observing others’ movements we can make predictions, and form expectations about the characteristics of objects that exist only in others’ minds.

The excitability of resting motoneurons increases following spinal cord injury (SCI). The extent to which motoneuron excitability changes during voluntary muscle activity in humans with SCI, however, remains poorly understood. To address this question, we measured F waves by using supramaximal electrical stimulation of the ulnar nerve at the wrist and cervicomedullary motor-evoked potentials (CMEPs) by using high-current electrical stimulation over the cervicomedullary junction in the first dorsal interosseous muscle at rest and during 5 and 30% of maximal voluntary contraction into index finger abduction in individuals with chronic cervical incomplete SCI and aged-matched control participants. We found higher persistence (number of F waves present in each set) and amplitude of F waves at rest in SCI compared with control participants. With increasing levels of voluntary contraction, the amplitude, but not the persistence, of F waves increased in both groups but to a lesser extent in SCI compared with control participants. Similarly, the CMEP amplitude increased in both groups but to a lesser extent in SCI compared with controls. These results were also found at matched absolutely levels of electromyographic activity, suggesting that these changes were not related to decreases in voluntary motor output after SCI. F-wave and CMEP amplitudes were positively correlated across conditions in both groups. These results support the hypothesis that the responsiveness of the motoneuron pool during voluntary activity decreases following SCI, which could alter the generation and strength of voluntary muscle contractions. NEW & NOTEWORTHY How the excitability of motoneurons changes during voluntary muscle activity in humans with spinal cord injury (SCI) remains poorly understood. We found that F-wave and cervicomedullary motor-evoked potential amplitude, outcomes reflecting motoneuronal excitability, increased during voluntary activity compared with rest in SCI participants but to a lesser extent that in controls. These results suggest that the responsiveness of motoneurons during voluntary activity decreases following SCI, which might affect functionally relevant plasticity after the injury.

Recent research suggests that eye contact can lead to enhanced self-awareness. A related phenomenon, the sense of agency deals with the notion of the self as the origin of our actions. Possible links between eye contact and agency have been so far neglected. Here, we investigated whether an implicit sense of agency could be modulated by eye gaze. We asked participants to respond (button press) to a face stimulus: looking or not at the participant (experiment 1); or displaying distinct eye gaze before or after a mask (experiment 2). After each trial, participants estimated the time between their key press and the ensuing effects. We found enhanced intentional binding for conditions that involved direct compared to averted gaze. This study supports the idea that eye contact is an important cue that affects complex cognitive processes and suggests that modulating self-processing can impact the sense of agency.

International audience; It has been suggested that tactile perception becomes less acute during movement to optimize motor control and to prevent an overload of afferent information generated during action. This empirical phenomenon, known as "tactile gating effect," has been associated with mechanisms of sensory feedback prediction. However, less attention has been given to the tactile attenuation effect during the observation of an action. The aim of this study was to investigate whether and how the observation of a goal-directed action influences tactile perception as during overt action. In a first experiment, we recorded vocal reaction times (RTs) of participants to tactile stimulations during the observation of a reach-to-grasp action. The stimulations were delivered on different body parts that could be either congruent or incongruent with the observed effector (the right hand and the right leg, respectively). The tactile stimulation was contrasted with a no body-related stimulation (an auditory beep). We found increased RTs for tactile congruent stimuli compared to both tactile incongruent and auditory stimuli. This effect was reported only during the observation of the reaching phase, whereas RTs were not modulated during the grasping phase. A tactile two-alternative forced-choice (2AFC) discrimination task was then conducted in order to quantify the changes in tactile sensitivity during the observation of the same goal-directed actions. In agreement with the first experiment, the tactile perceived intensity was reduced only during the reaching phase. These results suggest that tactile processing during action observation relies on a process similar to that occurring during action execution.

International audience; Temporal binding is understood as an effect in which a temporal interval between a voluntary action and its consequent effect is perceived as compressed. It denotes an implicit measure of a sense of agency. When people observe someone else performing an action that generates an effect, temporal binding also takes place. We aimed to test whether the interaction between observed actions and tactile sensation influences temporal binding. Participants observed finger tapping movements (of a human or wooden hand), in parallel to receiving tactile stimulations on their fingertip. These stimulations were either congruent or incongruent with the tactile consequences of the observed movement. The finger tapping movement was followed by a tone. Participants estimated the intervals between the observed action and the tone. We found that temporal binding for observed actions depends on the congruency between the perceived touch and tactile consequences of observed actions restricted to intentional actors.

International audience; Previous studies suggest that the sense of agency (SoA), the feeling of control about one’s own actions and ensuing effects is also generated during action selection processes. We investigate whether the conflict at the action selection stage induced by a supraliminal stimulus, modulates an implicit measure of SoA, namely intentional binding. Furthermore, we were interested to investigate the influence of different types of stimulus-response compatibility on SoA. To this aim we compared the influence of an automatic imitation task and a stroop-like task on intentional binding. In both tasks participants performed congruent and incongruent fingers movements (key release) in response to an external stimulus. Their movements caused an effect and participants estimated the time between their action and the ensuing effect. We found a reduced intentional binding effect in incongruent compared to congruent conditions in both tasks. The results are discussed within the theoretical framework of the fluency of action.

In order to survive in a complex environment, inhabited by potentially threatening and noxious objects or living beings, we need to constantly monitor our surrounding space, especially in the vicinity of our body. Such a space has been commonly referred to as one's 'peripersonal space' (PPS). In this study we investigated whether emotion-inducing approaching sound sources impact the boundaries of PPS. Previous studies have indeed showed that the boundaries of PPS are not fixed but modulate according to properties of stimuli in the surrounding environment. In Experiment 1, participants performed a simple tactile detection task of targets presented to their right hand. Concurrently, they were presented with intensity-changing task-irrelevant artificial sound sources perceived as approaching toward their body. The physical properties of the sound elicited emotional responses of either neutral or negative valence. Results showed larger PPS when the approaching stimulus had negative as compared to neutral emotional valence. In Experiment 2, we used ecological sounds which content (i.e., psychological associations to the sound producing source), rather than physical properties, elicited emotional responses of negative, positive or neutral valence. In agreement with results from experiment 1, we found larger PPS when the approaching stimuli had negative emotional valence as compared to both neutral and positive ones. Results are discussed within the theoretical framework that conceives PPS as a safety zone around one's body.

It is known that non-clinical subjects with high levels of schizotypal personality traits (High-S), as well as schizophrenic patients, have difficulties to judge how a scene would appear (so-called Appearance questions) from a point of view other than their own after having performed a disembodied perspective taking (D-PT, a mental self-rotation cued by an object like a chair). This inability has been defined allocentric simulation deficit. However, it is still unclear whether this inability might also regard an embodied transformation (E-PT), which is a self-rotation cued by another individual in the scene, and whether the observed deficit regards the pure mental transformation phase. In the present study, we took advantage of a virtual reality environment to explore both embodied and disembodied allocentric simulation in healthy volunteers with low and high levels of schizotypal personality traits, as assessed by the Schizotypal Personality Questionnaire. All subjects performed a pure self-rotation cued by a chair (D-PT) or by an avatar (E-PT), or a control array rotation. Each rotation was followed by classical Appearance and Item questions. Results revealed no between-groups differences in the mental transformation phase, while High-S subjects were significantly slower than Low-S subjects in the Appearance task after D-PT, but not after E-PT. Accordingly, higher schizotypy levels (cognitive-perceptual subscale) were positively correlated with slower reaction times in the Appearance task after D-PT. These data suggest the existence of a disembodied allocentric simulation deficit in non-clinical High-S, paving the way to future studies on clinical populations.