Tolerable Visuo-Tactile Inconsistencies in Periodic and Random Grating Textures on Surface Texture Displays

In surface tactile displays, consistency between visual and tactile feedback is generally regarded as critical. However, subtle inconsistencies between these modalities often go unnoticed by users. This study examines the tolerance for visuo-tactile gaps in texture perception, specifically focusing on grating scales, using a surface friction display. To encompass a wide range of textural stimuli, we employed both periodic and random gratings. Participants adjusted the tactile grating scales (average wavelength) to match visual grating scales, enabling the identification of 84% discrimination limens for two reference mean wavelengths: 1.0 mm and 2.0 mm. The minimally allowable inconsistencies, defined as the 84% discrimination limens, were measured as 0.315 mm and 0.422 mm for periodic gratings and 0.256 mm and 0.327 mm for random gratings at the 1.0 mm and 2.0 mm wavelength levels, respectively. Results showed that random gratings exhibited significantly narrower tolerance ranges compared to periodic gratings. These findings are valuable for the design of haptic content, as they inform the hardware performance specifications, particularly the precision required in sensing finger movements on touch panels.