Study on an Evaluation of Human Scratching Motions by Measuring Scratch Sounds

Itch is an unpleasant sensation associated with various disease, and can trigger scratching. Management of itch and scratching is important for treatment of disease. Therefore, quantitative and objective evaluation of itch and scratching is demanded. This work aims to develop the sensor system for evaluating the scratching motion. For the purpose, we focus on scratch sounds induced by scratching motion and, propose a nail mounted sensor system . In the sensor system a small microphone is attached on a nail for measuring scratching sounds. First, for investigating the relationship between the scratch sounds and the mechanical characteristics of human scratch motion, the artificial skin model made of polyurethane was used as a scratched object. The measurement system that can measure force and a motion of fingertip during scratching was constructed. Using the measurement system, various kinds of human scratch motions and sounds were measured. By signal processing of the scratch sounds, the several sound features were calculated and characteristics of scratch motions were extracted. Then, correlation coefficients between sound features and scratch motion properties were calculated. From the results, two pairs of the parameters were found as the most adequate parameter pair to evaluate the mechanical characteristics of human scratch motion. And using these parameters, “scratch evaluation map” was proposed as a method to evaluate the mechanical characteristics of human scratch motion. From the results, it was found that the developed sensor system has possibility to evaluate the mechanical characteristics of human scratch motion by the scratch sounds.