Mirroring multiple agents: motor resonance during action observation is modulated by the number of agents

Abstract

Although social situations regularly involve multiple persons acting together, research on the mirror neuron system has focused on situations in which a single agent is observed. Therefore, the goal of the current study was to explore the role of the mirror mechanism in situations involving multiple agents. Specifically, we used transcranial magnetic stimulation (TMS) to investigate whether mirror activation is modulated by the number of observed agents. Based on group contagion research, we hypothesized that multiple agents would provide a stronger trigger to the motor system and would therefore produce a stronger mirror response than a single agent. Participants observed movements performed by a single hand or by two hands while TMS was applied to the primary motor cortex. The results confirmed that activation in the motor system was stronger for two hands. This suggests that input to the motor system increases as the number of agents grows. Relating back to group contagion, our study suggests that groups may be more contagious simply because their actions resonate louder. Given that the mirror mechanism has been linked to a variety of social skills, our findings additionally have important implications for the understanding of social interaction at the group level.

Automatic imitation of multiple agents: A computational model

“…Simulation 1 aims to reproduce the first finding of Cracco et al (2015), namely that two hands performing the same action (2H ID) produce a stronger congruency effect than one hand performing a single action (1H). More specifically, it does so by implementing the hypothesis that identical actions activate the same motor representation (Cracco & Brass, 2018c, 2018aCracco et al, 2015Cracco et al, , 2016. As shown in Figure 3, the model captures the empirical results, with responses on congruent trials being faster and responses on incongruent trials being slower in the 2H ID condition than in the 1H condition.…”

“…Pointing in this direction, research looking at automatic imitation of multiple agents has shown that seeing two hands performing the same action elicits stronger corticospinal excitability (Cracco, De Coster, Andres, & Brass, 2016) and therefore stronger imitation (Cracco & Brass, 2018a;Cracco, De Coster, Andres, & Brass, 2015) than seeing one hand performing a single action. Similarly, research using four stimulus hands has shown that automatic imitation increases proportionally with the number of identical observed actions (Cracco & Brass, 2018c).…”

Cognitive Impact of Social Robots: How Anthropomorphism Boosts Performances

“…In the same way that we cannot refrain from recognizing a face or a word when we perceive it, we cannot help but represent in motor terms the actions we perceive. During interactions with humans, the information that leads to this activity is integrated automatically [48], [49] and is resistant to modulation by context [50], [51]. This system could be used to anticipate other people's actions [52].…”

Representing Multiple Observed Actions in the Motor System

“…Instead, to reach this conclusion, it has to be shown that multiple motor representations were activated. Therefore, in previous work, we have measured automatic imitation (Cracco et al 2015;Brass 2018a, 2018b) and corticospinal excitability (Cracco et al 2016) while participants observed either a single action or two identical actions. This revealed action-specific increases in both measures when two identical actions were observed, suggesting that both actions triggered the same motor representation.…”