Effects of Distributed Friction During Sliding Touch.

Friction modulation allows for a range of different tactile sensations and textures to be simulated on flat touchscreens, yet is largely unable to render fundamental interactions such as tracing the edge of a line or shape; an edge consists of straddling two different states, yet friction modulating screens traditionally apply only one friction force at a time to the whole finger. In order to expand the range of sensations rendered via friction modulation, in this paper we explore the possibility of applying spatial feedback on the fingerpad via differing friction forces on flat touchscreens. To this end, we fabricated six distinct flat surfaces with different spatial distributions of friction and calculated deformation of the fingerpad skin in response to motion along these physical samples. In our study, friction changes that occur sequentially along the sliding direction introduced little transitory spatial warping such as compression or stretching to the fingerpad, suggesting limited perceptual differences in comparison to 'classic' friction modulation. Distributing friction across the direction of motion, however, showed pattern-dependent shearing of the fingertip skin, opening avenues for new sensations and illusions heretofore unachievable on flat touchscreen surfaces.