Introduction: Vestibular illusions are the most common illusions that can cause spatial disorientation in flight. This study aims to find out whether and how the ability of keeping arm-hand posture is affected by the vestibular illusions induced by galvanic vestibular stimulation (GVS).
Methods: With their heads and trunks firmly fixed, 16 subjects maintained arm-hand posture under three GVS conditions (no stimulation, anode right, and anode left) for 10 s. Range of sway (RS), root mean square of displacement (RMS), and mean deviation (D) of the hand, as well as the rotation angle of the wrist, elbow, and shoulder in the horizontal plane, were measured. One-way ANOVA was used to analyze the effects of GVS on keeping arm-hand posture.
Results: With GVS, the hand deviated to the anode side continuously in the lateral direction, but moved at random in the sagittal direction. RS and RMS in the lateral direction were significantly increased by 89.0% and 104.7%, respectively. D was significantly increased about 6 mm to the anode. The shoulder joint and elbow joint always turned toward the anode, but the wrist joint turned at random. Furthermore, GVS polarity had no significant effect on the amplitude of each parameter.
Conclusion: GVS can decrease both the accuracy and precision of hand position, especially in the lateral direction. The continuous hand deviation to the anode side is mainly induced by the rotation of elbow and shoulder. Extra attention needs to be paid to these findings in future spatial disorientation studies.