Abstract
Central to the mechanistic understanding of the human mind is to clarify how cognitive functions arise from simpler sensory and motor functions. A longstanding assumption is that forward models used by sensorimotor control to anticipate actions also serve to incorporate other people’s actions and intentions, and give rise to sensorimotor interactions between people, and even abstract forms of interactions. That is, forward models could aid core aspects of human social cognition. To test whether forward models can be used to coordinate interactions, here we measured the movements of pairs of participants in a novel joint action task. For the task they collaborated to lift an object, each of them using fingers of one hand to push against the object from opposite sides, just like a single person would use two hands to grasp the object bimanually. Perturbations of the object were applied randomly as they are known to impact grasp-specific movement components in common grasping tasks. We found that co-actors quickly learned to make grasp-like movements with grasp components that showed coordination on average based on action observation of peak deviation and velocity of their partner’s trajectories. Our data suggest that co-actors adopted pre-existing bimanual grasp programs for their own body to use forward models of their partner’s effectors. This is consistent with the long-held assumption that human higher-order cognitive functions may take advantage of sensorimotor forward models to plan social behavior.New and Noteworthy: Taking an approach of sensorimotor neuroscience, our work provides evidence for a long-held belief that the coordination of physical as well as abstract interactions between people originates from certain sensorimotor control processes that form mental representations of people’s bodies and actions, called forward models. With a new joint action paradigm and several new analysis approaches we show that, indeed, people coordinate each other’s interactions based on forward models and mutual action observation.
Highlights
When we join a partner to lift a table, tango over a dance floor, or when we play the tuba in a musical band, we need to align our own actions with those of others
During bimanual grasping participants moved their hands on curved trajectories (Figure 2A for average trajectories aligned in percent of total travel time; subsequent analyses extracted data from individual trials) as commonly observed (Le and Niemeier, 2013a,b) (Supplementary Figure S1 for a quantification of the kinematics and timing variables of the control experiment)
Bimanual grasping showed features indicative of functional grasps: maximum grip aperture equivalent” (MGAe) values were smaller without perturbations than with perturbations [left and right rotation conditions averaged; t(10) = 4.61, p < 0.001, d = 7.226, Figure 2B], and increased with the horizontal object size with a gain of 0.401, which is significantly larger than zero [t(10) = 4.61, p < 0.001, d = 7.226]
Summary
When we join a partner to lift a table, tango over a dance floor, or when we play the tuba in a musical band, we need to align our own actions with those of others. Our brain uses feedback systems in which muscle activity occurs until a desired state of the body or of a body part has been attained, for example until a lower arm is bent as much as required to lift an object (e.g., Todorov and Jordan, 2002; Scott, 2004; Franklin and Wolpert, 2011). It has been argued that these internal representations, called forward models, have developed the ability to incorporate other people’s bodies and minds They might coordinate physical interactions with other individuals as well as abstract interactions and, constitute some of the seed mechanisms of human social cognition (Wolpert et al, 2003)
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