Movement interference during action observation as emergent coordination.

Previous research has demonstrated that when an actor coordinates with spatially incompatible movements of another individual that motor interference occurs-the rhythmic arm movements of the actor exhibit increased movement variability in the plane orthogonal (non-instructed) to the instructed plane of motion. Here we examine whether this motor contagion reflects not error but the spontaneous recruitment of additional task-specific movement degrees of freedom employed to withstand increasing task difficulty. Participants coordinated congruent and incongruent forearm movements with a confederate moving at a fast, moderate, and slow target frequency. Examining the variability in the non-instructed plane revealed oscillatory non-instructed plane movements that were coordinated with the instructed plane movements of the confederate. The results suggest motor interference during incongruent coordination can be understood as an emergent, task-specific property of the coordination goal.