Mechanical Impedance of the Hand Holding a Spherical Tool at Threshold and Suprathreshold Stimulation Levels

We report mechanical impedance of the hand for sinusoidal stimulation at the threshold and suprathreshold levels in the frequency range of 10-500 Hz delivered through a ball-shaped interface. The participants held the ball mounted on a minishaker in a way similar to that of holding a ball interface of a force-feedback device. A minishaker excited the ball in the vertical direction, resulting in vibrations on the skin of the hand in mostly the tangential direction. The position detection threshold curve was similar to that measured earlier using a stylus in the pen-hold posture, but the force detection threshold curve and the mechanical impedance was shifted upwards in the high frequency region. The mechanical impedance at the threshold and suprathreshold levels were essentially the same, indicating that skin characteristics do not change in the dynamic range of tactual perception for the same tool-holding posture