Communication of direction through lateral skin stretch at the fingertip

A variety of tasks could benefit from the availability of direction cues that do not rely on vision or sound. Skin stretch has been found to be a reliable means of communicating direction and has potential to be rendered by a compact device. We have conducted experiments exploring the use of lateral skin stretch at the fingertip to communicate direction. A small rubber cylinder was pressed against a subject's fingertip and moved at constant speed to stretch the skin of the fingerpad. The skin was stretched with a range of displacements (0.05 mm-1 mm) and speeds (0.5 mm/s-4 mm/s). Subjects were asked to respond with the direction of the skin stretch, choosing from 4 directions, each separated by 90 degrees. It was found that subjects could perceive skin stretch direction with as little as 0.05 mm of stretch. Direction detection accuracy was found to be dependent upon both the speed and total displacement of the skin stretch. Higher speeds and larger displacements resulted in greater accuracy. High accuracy rates, greater than 95%, were observed with as little as 0.2 mm of skin stretch and at speeds as slow as 2 mm/s. Accuracy was also found to vary with the direction of the stimulus. This preliminary information will be used to inform the design of a miniature tactile display suitable for use in hand-held electronics.