Effect of localized ambient humidity on electrotactile skin resistance

Electrotactile (electrocutaneous) stimulation produces controlled, localized touch sensations at the location of a small stimulation electrode by passing a small electric current through the skin. The electric field thus generated in subcutaneous tissue directly excites the afferent nerve fibers responsible for touch sensations. A number of factors influence the intensity, quality, controllability, and repeatability of electrotactile sensations on the fingertip. One of the most important of these is the ambient humidity of air surrounding the electrode-skin interface. The ambient humidity of air affects skin hydration which in turn affects skin impedance. As coaxial electrodes are used for stimulation, the air inside the coaxial electrode and the air surrounding the finger outside the electrode are two distinct volumes having potentially different humidity levels. The purpose of this study is to determine whether the humidity of air outside and or inside the coaxial stimulation electrode has a significant effect on the impedance of the electrode-skin interface. Results obtained by independently manipulating both the outside and inside humidity showed that there is no significant effect of outside humidity electrode-skin impedance is almost totally dependent on the inside humidity.