Abstract
In the velvet hand illusion (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. We investigate the VHI mechanism to obtain an effective hint for a new tactile display because such tactile illusions play a good role in deceiving the brain so that operators believe that a virtual sensation is real. To elucidate the VHI mechanism, we propose two approaches: one uses psychophysics to obtain human mental models; the other is a finite element method (FEM) to evaluate the tactile stimulus that causes VHI. In FEM analysis, a mesh model of fingertips is produced to mimic an actual finger to evaluate the strain energy density (SED) because one mechanoreceptive unit is a slowly adaptive mechanoreceptive type I unit (SAI) that well responds to SED. There is a considerable difference between the SEDs of the one-finger case and the two-finger case (VHI case): the peak SED value for the VHI case is around half of that for the one-finger case. The VHI mechanism 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 the wire-passing portion, causing operators to experience the illusion of touching a smooth virtual film with a zero coefficient of friction. Since VHI decreases with a decrease of wire spacing and an increase of the peak value of SED, excessive temporal stimulus generated by wire prevents VHI from increasing.
