Tactile Illusion Caused by Tangential Skin Strain and Analysis in Terms of Skin Deformation

We describe a new tactile illusion of surface geometry that can be easily produced with simple materials. When the fingertip skin is strained by loading it in traction along a narrow band surrounded by two fixed traction surfaces, the sensation of a raised surface is typically experienced. This and other analogous cases are discussed in terms of tissue deformation created at a short distance inside the skin where the target mechanoreceptors are presumably located. A finite element analysis allowed us to propose that the basis of this illusion is connected with the observation that normal loading and tangential loading can create similar strain distribution, thereby creating an instance of an ambiguous stimulus. In the discussion we relate this stimulus to several other ambiguous tactile stimuli.