VR devices can provide an unprecedentedly realistic visual experience, but they also demand higher comfort requirements. This is because the VR headset covers the entire visual range of the human eye, making it easier to immerse oneself but also more prone to causing dizziness. Motion sickness has always been a significant issue in VR experience, from a physiological point of view, 3D motion sickness occurs due to a mismatch between the sensory inputs that the brain receives from different systems that help maintain balance and orientation.
Normally, the brain uses three main systems to determine an individual's spatial orientation and movement:
- The visual system: which receives information from the eyes about the surrounding environment.
- The vestibular system: which is located in the inner ear and provides information about head position, movement, and acceleration.
- The proprioceptive system: which provides feedback about the position and movement of the body's muscles and joints.
In a 3D environment, such as in a virtual reality headset or 3D movie, the visual system may receive conflicting or exaggerated signals that do not match the signals from the other two systems. For example, the visual system may perceive rapid movement or changes in orientation, while the vestibular and proprioceptive systems do not detect any corresponding movement.
This mismatch in sensory inputs creates confusion in the brain, which perceives a potential threat to the body's balance and orientation. The brain then triggers a set of physiological responses, including nausea, dizziness, sweating, and fatigue, in an attempt to restore equilibrium.
One of the most important factors affecting dizziness in VR is MTP, which stands for Motion To Photons Latency. It refers to the time required from user action, sensor recognition, calculation processing, screen response, to final presentation in front of the user's eyes. The shorter the time, the better the device's immersion, and the longer the time, the stronger the user's dizziness. MTP below 20 milliseconds can greatly reduce the possibility of motion sickness. Human biological research shows that the delay between human head movement and visual feedback must be less than 20 milliseconds, otherwise it will cause visual dragging and lead to strong dizziness, which greatly destroys the VR immersion. The manifestation of this is that the user has completed an instruction input, but has not obtained the input result in synchronization, and there is a certain delay. In normal human perception behavior, when performing an action, the visual feedback and the input result of the action are almost completely synchronized. The delay in VR will greatly destroy the immersion and cause discomfort in the vestibular system, leading to dizziness. Therefore, the MTP requirement for VR is usually targeted at no more than 20 milliseconds.