  Playing back vibrotactile signals through actuators is commonly used to
simulate tactile feelings of virtual textured surfaces. However, there is often
a small mismatch between the simulated tactile feelings and intended tactile
feelings by tactile designers. Thus, a method of modulating the vibrotactile
perception is required. We focus on fine roughness perception and we propose a
method using a pseudo-haptic effect to modulate fine roughness perception of
vibrotactile texture. Specifically, we visually modify the pointer's position
on the screen slightly, which indicates the touch position on textured
surfaces. We hypothesized that if users receive vibrational feedback watching
the pointer visually oscillating back/forth and left/right, users would believe
the vibrotactile surfaces more uneven. We also hypothesized that as the size of
visual oscillation is getting larger, the amount of modification of roughness
perception of vibrotactile surfaces would be larger. We conducted user studies
to test the hypotheses. Results of first user study suggested that users felt
vibrotactile texture with our method rougher than they did without our method
at a high probability.Results of second user study suggested that users felt
different roughness for vibrational texture in response to the size of visual
oscillation. These results confirmed our hypotheses and they suggested that our
method was effective. Also, the same effect could potentially be applied to the
visual movement of virtual hands or fingertips when users are interacting with
virtual surfaces using their hands.
