The effect of fingertip microstructures on tactile edge perception

People rely on tactile edge localization to ascertain the location and structure of edges. When pressure is applied to the skin, skin mechanoreceptors convert compressive stress/strain into neural signals. Many attempts to model this conversion neglect intermediate ridges, on the inside of the stiff epidermis. The receptors associated with detecting compressive and shear stresses reside at the tips of these ridges, suggesting a functional importance in the detection of stress. This work considers how underlying microstructure affects the mechanical propagation of stress to receptors. Two unique indenters are applied to two finite element models of idealized, fingerpad skin - one with ridge microstructure. Findings indicate that microstructure produces high, local stress concentrations at ridge tips near receptors. Because stress is focused at ridges beneath edges, there is a higher contrast of stress between ridge tips near the indenter's edge and those adjacent. This lensing effect mechanism appears to help distinguish edges.