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 zero. 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 values and sem for each object curvature (see colormap of Fig. 1) and force direction are shown.