Abstract
Through highly precise perceptual and sensorimotor activities, the human tactile system continuously acquires information about the environment. Mechanical interactions between the skin at the point of contact and a touched surface serve as the source of this tactile information. Using a dedicated custom robotic platform, we imaged skin deformation at the contact area between the finger and a flat surface during the onset of tangential sliding movements in four different directions (proximal, distal, radial and ulnar) and with varying normal force and tangential speeds. This simple tactile event evidenced complex mechanics. We observed a reduction of the contact area while increasing the tangential force and proposed to explain this phenomenon by nonlinear stiffening of the skin. The deformation's shape and amplitude were highly dependent on stimulation direction. We conclude that the complex, but highly patterned and reproducible, deformations measured in this study are a potential source of information for the central nervous system and that further mechanical measurement are needed to better understand tactile perceptual and motor performances.
Highlights
During object manipulation or tactile exploration, humans experience frequent partial or complete relative slippages between their fingertips and a contact surface
Considering the importance of cutaneous feedback in object manipulation [2,3], researchers have long thought that these partial slips were responsible for triggering a reactive grip force [4]
The contact area decreased, and the stuck area monotonically decreased to zero, which was defined as the instant of full slip
Summary
During object manipulation or tactile exploration, humans experience frequent partial or complete relative slippages between their fingertips and a contact surface. These events provide information about the mechanical properties of the surface (e.g. friction, surface roughness, shape, etc.). We showed that complete slippage occurs gradually, with the first ‘incipient’ slips occurring at the periphery of the contact, and an annulus of slip forming around a remaining ‘stuck’ zone [1]. As the tangential stress increases, this slipping area grows from the periphery to the centre, until the whole contact slips. This ‘stick-to-slip’ behaviour has crucial implications in dexterous manipulation and haptics. Each deformation event at the contact interface generates potential information for the central nervous system
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