Fig. 1

A Finger apparatus attached to the robot. B Notation system for describing target directions in x, y, and z axes. An example of visual feedback is shown for the experimental (C) and control (D) groups. Thumb force is shown as a blue ladder (composed of the two blue parallel lines and X in the center). Finger force is shown as a red ladder. The location for the center of the ladder (X) is determined by the digit force in the x and y direction, relative to the zero (the cross in the center). Digit force in the z direction is shown as the “fill” of the ladder. The goal is to place the center of the ladder inside the target, while matching the fill to the fill target. The actual force in all 3 directions is shown in the visual feedback to the experimental group (C). The actual force vector in the x and y directions is shown for illustration purposes only in E. For the control group, the same actual force is projected to the target direction in 3D (F, showing only 2 axes for illustration only). The projected force is shown for visual feedback for the control group (D)