Why does virtual reality make some people feel sick?

Virtual reality (VR) technology, which immerses people in real or imagined environments via a head-mounted display (HMD), can be used for entertainment, education, skills training and medical rehabilitation. It can also be used to help teach complex skills when real environments are too dangerous, like mine rescuers’ safety training. But despite advancements in VR technology, an illness called ‘cybersickness’ stands in the way of widespread VR use.

Dr Juno Kim from UNSW Science’s School of Optometry and Vision Science describes cybersickness as an umbrella term for illness caused by using a computer display. Dr Kim likened the health condition to motion sickness, as it usually includes symptoms like dizziness, nausea, eye discomfort and disorientation.

“But while motion sickness is a sensory mismatch between what we see and what our other senses signal about our motion, cybersickness doesn’t require physical movement,” said Dr Kim.

This mismatch, known as ‘sensory conflict’, occurs when visual pieces of information received by the eyes are disconnected from, or in direct challenge to, information received by other senses. The vestibular system, which is responsible for spatial orientation and sense of balance, recognises this discord. While the severity of cybersickness varies from person to person, the symptoms can be long-lasting.

“Evidence tells us cybersickness has negatively affected the widespread use of HMD VR by everyday consumers. By better understanding cybersickness, we can find hardware and software solutions to reduce it,” said Dr Kim.

There are many scientific theories explaining why people feel cybersickness. The ‘poison theory’ suggests cybersickness is the central system’s attempt to protect the body from a hazard (as it does with poison), while the ‘eye-movement’ theory suggests cybersickness is caused by inappropriate eye movement, eye strain and difficulty focusing. While there is no consensus on why people become ill in VR, it is accepted that display lag — the delay in the virtual scene keeping up with the actual movements — is a key contributing factor.

“Early HMDs had inherent display lag. These display lags were well known to cause significant cybersickness. With recent advances in the development of this technology, new HMD devices like the Oculus Rift S and Quest now achieve extremely low display lags. But latency spikes can occur from time to time, which appear to generate bouts of cybersickness,” said Dr Kim.

Researchers are using these fast-loading HMDs to better understand cybersickness in general. Using these state-of-the-art displays, researchers can deconstruct them by adding lag to see the impacts it has on cybersickness. Dr Kim and his team have been working on finding a way to measure the likelihood of experiencing cybersickness.

The team found that cybersickness could be explained by the level of ‘scene instability’ (the amount the virtual environment rotates in relation to the head’s real rotation). If a person in VR turns their head, the virtual head will follow, but won’t quite keep up in time and space. As the virtual environment adjusts, the ground appears to be unstable, even though the physical ground remains still. The angular difference between the virtual and physical head (known as Difference in Virtual to Physical, or DVP) was found to create the illusion of an unstable environment and account for the severity (and likelihood) of experiencing cybersickness.

Researchers asked 30 participants to move around a virtual space while wearing a HMD, the Oculus Rift CV1. While this HMD usually has a baseline lag of less than 5 ms, the researchers added artificial lag to put the users’ real and virtual movements out of sync. Participants reported their perceived scene instability range in each trial using a gauge and reported their cybersickness on a 20-point scale. As the display lag increased, so did the participants’ cybersickness and scene instability.

“We essentially created an objective geometric model to account for sensory conflict. The scene instability theory is the first to generate a testable hypothesis for understanding cybersickness and its causes,” said Dr Kim.

Measuring and tracking cybersickness could help make HMD VR experiences safer and more enjoyable. This model could help researchers create solutions to minimise cybersickness, such as wellbeing add-ons that indicate when someone has had a rough VR experience and might need to take a break.

“Now that we have instantaneous information about how much peak difference in DVP someone has been subjected to, we may have a way of predicting the likelihood that they are going to get sick. Cybersickness solutions could benefit the global community by providing better access to future ways of working, educating, training and communicating,” said Dr Kim.

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