Psychophysics and Perceiving Granularity

Recent research in hifi telerobotics is engaged in advancing human-system-interfaces displaying tactile and proprioceptive information, for example to improve the operator´s feeling of remote surface textures. An approach to the question of data reduction is to only transmit that information which humans can actually discriminate. There has been some research on the relationship between granularity perception and vibrotactile coding, but predicted differential sensitivity has not been systematically investigated. In order to address these issues, two psychophysical experiments were conducted. The threshold of detecting granularity was significantly lower when exploring the surface by scanning than by pressing the fingertip into it, but discrimination capacity of coarse granulated textures was higher when gently pressing the fingertip into the surface. The exploration of textures by pressure revealed decreasing sensitivity with decreasing spatial periods, whereas exploring the surface structure by scanning yielded a more complex relationship, which can be interpreted as being in agreement with sensitivity to temporal frequency.