Do Gaze Behaviours during Action Observation Predict Interpersonal Motor Resonance?

Reading out bodily cues to predict interactions

Successful motor coordination in social interactions requires the rapid interpretation of others' intentions from their actions. Previous research suggests that individuals use early bodily cues, such as movement kinematics and gaze, to predict others' behaviour. However, the motor features critical for signaling or decoding potential motor interactions remain unclear. In this study, we measured the kinematics of a basic motor act - grasping an object - executed with either individualistic (to place) or social (to pass) intentions. Subsequently, we conducted two action prediction tasks to identify bodily markers of (social) intentions. Hand positioning on the object emerged as a key kinematic indicator of the intention to interact with a partner, as shown by kinematic analyses and classification of participants' responses. Eye-tracking analysis revealed the face as the most attended feature during action observation. Notably, these cues were more consistently attended to when observing actions from a frontal - second-person - perspective rather than a lateral - third-person - perspective. Our findings highlight the saliency of hand-object interactions and the face in decoding potential engagement in second-person contexts. They also provide novel evidence for social affordance processing, expressed in action execution and observation, related to potential motor interactions with others. These features in decoding potential engagement in motor interactions.

Impact of Observation Duration in Action Observation Therapy: Manual Dexterity, Mirror Neuron System Activity, and Subjective Psychomotor Effort in Healthy Adults

Background/Objectives: Action observation therapy (AOT) has gained attention as a rehabilitation method for motor function recovery following nerve injury. Although the total observation time and daily session duration have been studied, the effective observation duration per trial remains unclear. This study examined the effect of different observation durations on manual dexterity, mirror neuron system activity, and subjective psychomotor effort in healthy adults. Methods: Twenty-four healthy right-handed adults participated in this crossover study under four conditions: observing ball rotations with the dominant hand for one, two, or three minutes, or geometric patterns (control) for two minutes. The outcomes included maximum rotations and errors by both hands during a ball rotation task and interpersonal motor resonance (IMR), indicating mirror neuron system activity. These measures were compared before and after intervention. Subjective ratings of concentration, physical fatigue, and mental fatigue were assessed post-intervention. Results: Rotation performance significantly increased for the intervention hand after a 2 min observation and showed a notable effect (p = 0.113, r = 0.48) for the non-intervention hand after a 3 min observation compared to the control. The IMR was significantly greater during the 2 min observation than in the control. Compared to the 1 min observation, the 2 min and 3 min observations resulted in higher mental fatigue, and the 3 min observation showed lower concentration levels. Conclusions: These findings indicate that the observation duration has varying effects on manual dexterity and mirror neuron system activity, with optimal effects observed at specific time intervals while also highlighting the relationship between observational learning and psychomotor effort.

Is there a relationship between EEG and sTMS neurophysiological markers of the putative human mirror neuron system?

The mirror neuron system (MNS) has been theorized to play a neurobiological role in a number of social cognitive abilities and is commonly indexed putatively in humans via interpersonal motor resonance (IMR) and mu suppression. Although both indices are thought to measure similar neuronal populations (i.e., "mirror neurons"), it has been suggested that these methods are unrelated, and therefore, incompatible. However, prior studies reporting no relationships were typically conducted in small and underpowered samples. Thus, we aimed to investigate this potential association in a large sample of neurotypical adults (N = 116; 72 females). Participants underwent transcranial magnetic stimulation (TMS), electromyography (EMG), and electroencephalography (EEG) during the observation of videos of actors performing grasping actions in order to index IMR and mu suppression (in beta, lower alpha, and upper alpha bandwidths). A series of linear regressions revealed no associations between IMR and each of the mu suppression bandwidths. Supplementary Bayesian analyses provided further evidence in favor of the null (B₀₁  = 8.85-8.93), providing further support for no association between the two indices of MNS activity. Our findings suggest that these two measures may indeed be unrelated indices that perhaps assess different neurophysiological aspects of the MNS. These results have important implications for future studies examining the MNS.