Experimental Set-Up.

A) Planar arm movements were made while each subject grasped the handle of a two-joint planar robot. Optical encoders provided measurements of position data, which was converted to a global x (medial/lateral) and y (forward/backward) coordinate system. Tasks were projected onto a horizontal screen, which obstructed the subject’s view of their hand and arm. The subject’s arm was supported by an armrest and the base of the pronated wrist was attached to the robot’s manipulandum with a wrist brace. Grip pressure was measured by a pressure bladder, which was placed in the subject’s palm. Subject depicted in figure is a computer generated image and is in no way representative of any actual subject. B) Twenty trials were conducted in each experimental condition totaling 200 trials. Initially, two blocks of trials were conducted to quantify baseline movement in proximal and distal workspace. Then in one workspace (proximal or distal) a block of trials was conducted measuring the response to a divergent force field (Fd). Tendon vibration was applied in the following block, in addition to Fd, to determine the effect of vibration on the ability to stabilize the hand at the end of movement. Aftereffects of vibration were evaluated during a block of trials with only Fd, which was followed by another block of baseline trials. The treatment and washout blocks were then repeated in the other (proximal or distal) workspace.