An investigation of tactile illusion toward tactile displays using psychophysical experiments

In this paper, a basic study for breakthrough in tactile presentation technology is described to progress tactile displays using velvet hand illusion (VHI). In the VHI, a person rubs his/her hands together on either side of wires strung through a frame, producing the sensation of rubbing a very smooth and soft surface like velvet. Since in VHI human subjects feel the surface like velvet that does not actually exist, we might develop a new tactile display capable of generating feeling of material based on the mechanism of VHI. The objective of this study is to elucidate this mechanism. We investigate the VHI using frames equipped with two parallel wires and a series of psychophysical experiments. According to the experiments using Thurstone's Paired Comparison, the strength of VHI depends on the wire distance and movement stroke, and VHI caused by passive touch is considerably stronger than that caused by active touch. This result suggests that VHI is controlled by mechanical external stimulation using tactile displays. Furthermore, we found that the strongest VHI is obtained at movement stroke r being approximately equal to wire distance D. According to the abovementioned results, the mechanism of VHI is assumed as follows: although the area bounded by two wires moves relative to the hands, tangential force does not occur on the hand surface except for wire-passing portion, causing operators to experience the illusion of touching a smooth virtual film with a zero coefficient of friction. Since VHI becomes weaker with a small distance between two adjacent wires or a large movement stroke, excessive tangential stimulation prevents the occurrence of VHI.