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By recent development of HMD technology, it becomes possible to provide a feeling as if his own intrudes into the VE. HMD is a wearable visual equipment used by being mounted on a human head, so user can retract into VE without seeing the outside of the information by blocking the outside world information and reflecting only VE image in front of user's eye. Therefore, using HMD is possible to reproduce a roller coaster experience, freely exploration of virtual house, etc.
Nagai et al. (Mon,) studied this question.