Figure 1.

Experiment setup. (A) shows frontal and side views of the handle used for the study (“a” denotes force/torque sensors). (B) shows the frontal view of the handle with thumb and index fingertip center of pressure of the reference hand located at the same y-coordinates (vertical height relative to the base of the object) on the graspable surfaces of the handle (collinear d_y). The red dots denote the CoP of each digit. (C) shows a top view of the experimental setup. The subject is shown contacting the handle with thumb and index fingertip, while the left hand was kept flat on the table. When relaxing in between trials, both hands were kept flat and relaxed. Note that the table top (gray) was opaque and prevented subjects from seeing their forearms and hands but is shown as transparent for graphical purposes only. Forearms and wrists were strapped to the table to prevent movements within and across trials while the handle was anchored to the table.