Hand setup and submaximal force-matching task.

(A) Subjects pressed with a custom-molded thermoplastic splint on the index finger onto a force sensor; both surfaces were covered with Teflon or 320-grit sandpaper to create low- and high-friction conditions, respectively. Forces were measured normal to the sensor surface (F_z), as well as in medial/lateral (F_x) and dorsal/palmar (F_y) directions. (B) Subjects increased force up to the target force (dashed line) within 3 s and held their force magnitude (black lines) as close to the target line as possible for 10 s. Gray highlighted areas indicate the time epochs where subjects received visual and no visual feedback.