Fig. 8.
Modulation of reflexes elicited by perturbations applied along the primary and secondary axes of endpoint stiffness during interactions with equal strength environments (experiment 2). A: average stretch recorded from clavicular head of pectoralis major (PECTCLAV) and posterior deltoid (PD) in a single subject during interactions with each destabilizing environment. Perturbations were applied in the directions indicated by the black arrows at the top of each column. Gray traces are the reflexes elicited during interactions with the environment aligned to the direction of maximal endpoint stiffness and black traces correspond to reflexes elicited during interactions with the orthogonal environment. B: average reflex EMGs, at matched levels of background muscle activity, for the group. Perturbation directions are as indicated in A. Colors correspond to the environment with which subjects interacted, as indicated by the characters at the bottom of the figure. Error bars SE. Asterisks, P < 0.05.