Fig. 2. Coordination of force and torque illustrated for selected single trials in experiment 2. A–D, Time traces showing (from top to bottom) the average grip force, the total torque on the digits (solid line), the torque predicted from regression (thin line), the torque on each digit, the angle of tilt, and the first and second time derivative of the tilt angle.E–H, Plots of grip force versus torque for each digit. In A and E, the object was tilted slowly (rise time, 0.90 sec). In B and F, the tilt was more rapid (rise time, 0.41 sec). In C andG, the object was returned to the vertical slowly (fall time, 1.11 sec). In D and H, the return was more rapid (fall time, 0.38 sec). The regression predicting torque had correlation coefficients of 0.997, 0.996, 0.998, and 0.996, inA, B, C, andD, respectively. Target torque was 74 mNm, and grasp surfaces were flat.