Motion encoding in touch relies on multiple cues, such as displacements of traceable texture elements, friction-induced vibrations, and gross fingertip deformations by shear force. We evaluated the role of deformation and vibration cues in tactile speed discrimination. To this end, we tested the discrimination of speed of a moving smooth glass plate, and compared the precision of the responses when the same task was performed with a plate having a fine texture. Participants performed the task with and without masking vibrations. Speed discrimination was nearly as precise among the two surface types, as assessed by the steep slope of the psychometric function. Consistent with our previous work, high-frequency vibrations impaired the ability of the participants in discriminating surface speed. Results of the current study showed that it is possible to discriminate motion speed even in absence of a raised texture. Highlights 1 • On a smooth surface, humans are able to discriminate the speed of a 2 moving surface by frictional motion cues 3 • The precision of speed discrimination is nearly the same with smooth 4 and fine-textured surface types 5 • High frequency vibrations impair the ability to discriminate speed of 6 moving surfaces 7 It provides feedback for the manipulation of handheld objects [2], and for 11 guiding hand reaching towards a target goal while touching a surface [3, 12 4]. During grasping tasks, our sensorimotor system rapidly adjusts the grip 13 force based on the small slips between the object and the skin, revealed as 14 vibrations [5].
15Different cues contribute to the perception of motion in touch, includ-16 ing the spatiotemporal pattern of skin indentation, as for example the one 17 generated by the tip of a pencil moving across the skin, high-frequency vi-18 brations caused by frictional slips, and the gross deformation of the skin 19 and subcutaneous tissues, such as the stretch generated by a shear force 20 applied to the fingertip [6, 7, 8, 9, 10]. The role of the first two motion 21 cues, local indentation and vibrations, was investigated in several studies 22 [11, 12, 13, 14, 15, 16, 17, 18]. Here, we investigated the discrimination of 23 speed of a smooth movable surface (i.e., a glass plate for microscope slide).
24Because of the lack of fine and coarse texture, shear deformation cues may 25 play an important role for this type of stimuli. Before introducing our study, 26 we will summarize recent findings about different cues in tactile motion per-27 ception.
28The indentation produced by traceable surface elements, like raised ridges 29 of the tip of a pen, provide a salient motion cue in touch [6, 11, 13]. For 30 instance, the perceived speed of a ridged surface depends on the distance 31 between its ridges, such as the closer the texture elements, the faster is 32 the perceived speed [12, 19]. In accordance with behavioral studies, a model 33 based on the spatiotemporal pattern of skin deformation, as the one produced 34 by a coarse texture, accurately reproduced tactile affere...