An experiment on tracking surface features with the sensation of slip

This paper describes the last of three experiments that investigate relative motion between a surface and the fingertip (slip) as part of a larger program of research on "fingertip haptics". To confirm the suspicion that tangential displacement of the skin during contact contribute to the perception of feature movement, this experiment tasks subjects to follow a feature on a surface that displays the path tangent given three different factors: the first factor is the absence of tangential displacements 1) within the contact area and 2) on the whole finger pad. The second factor explores different surface speeds. Finally, we explore different rates of path curvature. A custom mechanical filter placed between the skin and the moving surface enables the selective elimination of tangential contact displacements. Thirty-three subjects completed the tracking test, showing that the absence of tangential forces from slip severely impairs performance. However, results reveal heightened performance with the filter in a "loose" configuration. The performance suggests that subjects do not use shape alone to track features, but some combination of shape and tangential forces (due to friction) together to perceive the movement of small features.