Fig 2. Explicit observation condition.

(A) H-reflex amplitude modulation recorded in the right FCR muscle of 14 right-handed observers, during observation of one cycle of a flexion-extension movement of the mover’s right hand (B, average movement trace performed by the mover in all different experiments (±SEM)). In panel A the cumulative plot of the average data points from all subjects is fitted with a sinusoid equation with the same period as that fitting the movement. H-reflexes are significantly modulated, showing that increasing excitability of the flexor motorneuronal pool develops during the flexing phase of the observed movement. Δϕ: phase difference between reflex modulation in flexor muscle of the observer and hand oscillation of the mover. For easier graphic visualization of the parallel time course of the two events, hand flexion (Flex = downward direction of the moving hand) is drawn in the upper direction. (C) Graphic representation of this, and all following experiments.