The present study investigated whether vection could be modified by an object grasping movement. Twenty-five university students were asked to do one of the following four types of left-hand movements while they were viewing a radial optic flow: (1) grasping the hand-gripper strongly; (2) holding the hand-gripper; (3) clenching fist strongly; and (4) open hand without having anything in their left hands (normal hand condition). The participants’ tasks were to keep pressing a button with their right hands while they were perceiving vection. After each trial, they estimated the subjective strength of vection on a 101-point scale. The result showed that the vection was inhibited by strongly grasping the hand-gripper task more than by the other hand movements. Vection could be weakened by the object grasping movement. It might be suggested that vection could be inhibited by the presence of an object being grasped and also by the grasping movement itself. We speculated that the mechanism underlying this inhibition might be related to cognitive pressure, attentional load, power and muscle tonus, and multisensory and proprioception interactions.
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