Assessment of virtual light touch phenomenon by vibrotactile stimulation control based on body sway

An increasing frequency of fall accidents associated with demographic aging in Japan has given rise to a need for effective fall prevention methods. Elderly people often use support devices such as canes and walking frames to reduce the risk of falling, however such solutions may be inappropriate for certain environments. Previous research has shown that unsteadiness can be mitigated via light touch contact (LTC) with a force of up to around 1 N with curtains or similar (Jeka, 1994), and the authors also previously proposed a virtual light touch contact (VLTC) approach based on LTC (Shima et al., 2013). VLTC supports standing stability based on a surrounding virtual partition connected to a vibrotactile fingertip stimulator. Here, it is known that the VLTC effect is not achieved via simple constant fingertip stimulation. Thus, vibrotactile stimulation is in VLTC needs to be controlled based on fingertip motion characteristics such as acceleration. However, LTC effect can be achieved via constant contact fingertip with a piece of paper or similar without fingertip movement. Assuming that reaction force from a fixed point fluctuates with body sway or psychological tremors in LTC, the LTC effect may be achievable by reproducing such fluctuations via vibrational stimulation. In this study, the authors proposed a novel VLTC method involving the use of vibration stimulation control to reproduce fluctuations in contact reaction force caused by the individual's movement based on fingertip acceleration data. Verification of the method indicated the proposed method can reduce body sway and reproduce the LTC effect. This suggests that reduction may be associated with slight improving fingertip positional sense.