Response of SAI Afferents May Play a Role in the Perception of Velvet Hand Illusion

Problem statement: We revealed the reason behind a haptic illusion called the Velvet Hand Illusion (VHI) by FEM analysis. In VHI, a person rubs his/her hands together on both sides of wires strung through a frame and produces the sensation of rubbing a very smooth and soft surface like velvet. We focus on VHI to determine the specifications of an actuator for a tactile display enhanced by VHI. Approach: A simulated fingertip was modeled under the same contact condition that an actual finger was believed to undergo when under VHI. We collected the simulated responses of a number of SAI afferents, which were responsible for detecting the edges, to relate them to the mechanism of the illusion. Results: Even with a simple model that treats only one finger, we noticed a considerable difference between the responses of a number of SAI receptors compared with that of a fingertip touching wires without the effect of the opposing finger. The SAI responses for the VHI case are less (some receptors’ response is up to 50% less) than those for a finger touching the wires, which corresponds to a decrease of the perception of the wires. Conclusion/Recommendations: SAI might play a role in the mechanism of the VHI illusion. This study could benefit the development of a haptic display that utilizes the illusion and makes a person experience the same feeling using the proposed display.