Fig. 3.

Experimental variables and grasp phases. The time courses of the experimental variables and grasp phases are shown for 1 representative trial. Shown from top to bottom are grip force averaged across thumb and index fingers and load forces exerted by the thumb and index finger (dashed and gray solid lines, respectively), vertical height of the object, and object roll; the solid line denotes compensatory torque, whereas the dashed horizontal line denotes the target torque subjects had to exert to counter the external torque caused by the added mass at the bottom of the object. Time epochs shown are “Go” signal (a), grip force onset (b), load force onset (c), and lift onset (d) (see text for details). The “Go” signal was given to subjects 2 s after the contact and sense phase (see Fig. 2C) to cue the subject to initiate object lift.