Figure 10.

A comparison of the predicted and observed manifold along which the endpoint stiffness (K_xx and K_yy) should modulate as task difficulty increases. A, Simulated kinematic variability (SD_y) for the main study (negative x-force production direction). A clear dependence of K_xx and K_yy is visible (see also Fig. 7). For the simulations, K_xy = −150 and curvature was 0. B, Simulated kinematic variability for the second study (positive y-force direction). Now the kinematic variability (SD_x) depends almost entirely on K_xx. C, The manifold along which the experimental results align. Regression lines of K_xx and K_yy through the experimental results for the main study (negative x; red) and second study (positive y; blue). Also the mean ± SEM values for each object curvature (see color map of Fig. 1) and force direction are shown.