Control method of kinesthetic illusion using natural frequency of tendon toward compact rehabilitation devices

To develop devices of neurorehabilitation for the stroke patients, we focus on the Kinesthetic Illusion (KI), which is a proprioceptive illusion phenomena. In KI, we feel the joint movement sensation without actual movement, when the vibrating stimulation is applied to a specific tendon. In KI research, it is very important to clarify the optimal condition to induce the stronger illusion, which has not yet been clarified. In this study, we try to clarify the optimal condition for inducing KI from the view point of vibration engineering. This result will contribute toward development of a new mechatronics system inducing KI. In order to the abovementioned investigation, we assume that there is an important relationship between a natural frequency of the specific tendon and the optimal frequency for KI. We focus on the tendon of the Flexor Carpi Radialis muscle (FCR) which is related to the wrist joint movement in the extended direction and conduct a series of psychophysical experiments. As a result, a correlation of R = 0.50 is found between the optimal frequency for KI and a natural frequency of the tendon. This result demonstrates that the joint moving sensation of limbs can be controlled through a basic vibrating stimulation to induce KI by means of applying the natural frequency of the specific tendon.