Analysis of Humans Capability to Discriminate Multidimensional Forces at the Big Toe

Abstract

Tactile sensation represents an essential skill for tasks of daily living. However, people that are depending on auxiliary devices, like hand prosthesis or assisitve-robotic arms, have to life mostly without this skill. In most of the commercially available active hand prosthesis only an open-loop control is possible. Usually no haptic information is provided to the user. Given that the glabrous skin of the feet provides a similar sensory structure as the glabrous skin of the hands, a new approach for haptic feedback could be applying haptic information to the toes. During object manipulations with the hands the human perceives and processes multidimensional forces in the human hand. This master thesis analyzes whether humans have the capability to discriminate multidimensional forces also at the big toe. Using a modified state-of-the-art haptic feedback device open-loop tests with 24 healthy subjects were performed. Tangential displacements from 0° to 25° were provided to the subject’s right big toe while contact forces of 2N, 5N or 8N were applied. In total the four different directions of up (distal), down (proximal), left (medial), and right (lateral) were tested. The results showed that within defined proportions of the tangential force a directional discrimination was possible at 5 N and above. The tangential displacement as well as the total acting force showed an influence to the results. The four different directions showed no affect across all subjects