Creating Tactile Motion

Abstract

Interactions with the world and between our own body parts often result in motion across the skin, and sensory processing of this motion is of interest to both basic and applied researchers. We describe motion cues and common approaches to creating tactile motion to help researchers make choices for their study, and we give two illustrative examples. Major cues that inform about direction and speed of tactile motion are displacement over the skin, skin stretch, and skin vibration. The most common approach for creating tactile motion relies on apparent motion, the motion sensation arising from discrete—often vibrating—stimuli presented in quick succession to simulate object displacement. Other methods rely on real displacement of objects such as plates and brushes. They create friction and skin stretch, allowing the study of that cue and resulting in a richer motion experience. Friction can also be implemented in devices that rely on apparent motion, but this is still very rare. Some recent solutions, such as movement-contingent air turbulation, are driven by the desire to create immersive tactile experience in virtual reality. Illusions abound in perception of motion, as in any other aspect of perception. They include mislocalization of discrete motion stimuli known as sensory saltation, and filling-in of non-stimulated skin area with the sensation of continuous motion—the two effects we focus on in the Methods section. We use them to illustrate two manners of motion delivery (discrete stimulation vs real object displacement) and a variety of ways to measure perception of the moving stimulus.