dissertationThe study of haptic interfaces focuses on the use of the sense of touch in human-machine interaction. This document presents a detailed investigation of lateral skin stretch at the fingertip as a means of direction communication. Such tactile communication has applications in a variety of situations where traditional audio and visual channels are inconvenient, unsafe, or already saturated. Examples include handheld consumer electronics, where tactile communication would allow a user to control a device without having to look at it, or in-car navigation systems, where the audio and visual directions provided by existing GPS devices can distract the driver's attention away from the road. Lateral skin stretch, the displacement of the skin of the fingerpad in a plane tangent to the fingerpad, is a highly effective means of communicating directional information. Users are able to correctly identify the direction of skin stretch stimuli with skin displacements as small as 0.1 mm at rates as slow as 2 mm/s. Such stimuli can be rendered by a small, portable device suitable for integration into handheld devices. The design of the device-finger interface affects the ability of the user to perceive the stimuli accurately. A properly designed conical aperture effectively constrains the motion of the finger and provides an interface that is practical for use in handheld devices. When a handheld device renders directional tactile cues on the fingerpad, the user must often mentally rotate those cues from the reference frame of the finger to the world-centered reference frame where those cues are to be applied. Such mental rotation incurs a cognitive cost, requiring additional time to mentally process the stimuli. The magnitude of these cognitive costs is a function of the angle of rotation, and of the specific orientations of the arm, wrist and finger. Even with the difficulties imposed by required mental rotations, lateral skin stretch is a promising means of communicating information using the sense of touch with potential to substantially improve certain types of human-machine interaction
