Addressing the Myths About Head Mounted Display Use in Balance Assessments and Rehabilitations
In this post we will discuss the advantages and disadvantages of using Head Mounted Displays (HMD) as an immersive virtual reality platform. We will also show you how HMD/VR technology may be applied in a clinical setting and discuss how to reduce some of the symptoms subjects may notice with their use.
An HMD system can provide a cost and space effective, immersive environment to enhance balance evaluation. Controlling what the subject sees while taking center of pressure (COP) measurements opens a whole new area for assessing and treating a variety of balance disorders. After all, balance is one part vestibular, one part somatosensory, and one part vision. The HMD gives a clinician the ability to immerse the subject in a controlled visual simulation to evaluate their visual spatial skills and COP measurements as we alter their central and some of their peripheral visual clues, among other things.
What are the key differences between augmented reality (AR), virtual reality (VR) and other immersive environments?
Both AR and VR are gaining in popularity as digital tools for business, medical, and entertainment applications. Virtual reality is not just for gamers anymore; it has become a valuable tool for many professions, including healthcare.
AR basically superimposes a digital image or effect over the real-world image. This may be a static snapshot of your living room with a digital image of the new chair you are considering buying and want to see how nice it might look in the corner. AR would enable you to overlay a digital image of that chair into the corner of the room. You could also change the style, color, or size of the digital chair at will. Most of the image is actual, or real, and the subject tends to feel more “grounded” or comfortable because of it. As a result of this sense of “grounding,” there are less motion sickness symptoms, balance issues, and visual distress. These symptoms are often referred to as VRISE or Virtual Reality Induced Symptoms and Effects.
With VR, you would not see any real-world image; you are totally immersed in digital simulation of the living room. You can change chair variables as well as change the size of the room, the colors of the walls-almost anything you want. This allows the program to digitally control every aspect of the images including speed of movements, contrast, field of view, and the horizontal and vertical spatial orientations. Although the quality of the graphics and programming continues to improve at an amazing rate, it is still virtual and not real.
Another type of immersive reality is known as CAVE (Cave Automatic Virtual Environment), which is a physical environment in which the sidewalls, ceiling, and most of the floor is virtually simulated, but some of the floor and the world behind the subject is open, like a cave would be. (3) Because they retain some real-world clues, such as being able to see their feet, the patient is less immersed and therefore able to stay more grounded in the real world. This environment has a tendency to reduce VRISE symptoms compared to a totally immersed HMD system. In the Bertec Computerized Dynamic Posturography (CDP/IVR) this is accomplished with a large dome and sophisticated projector system, which also allows for a 200+-degree field of view verses the 100 degrees of an HMD. To recap, although the HMD has the most immersive environment, its field of view is significantly less than the CDP. The CDP gives us the best of both worlds by having a 200+ degree field of view and a very controllable environment, but still allowing the patient to feel connected to the real world, which reduces the VRISE symptoms. Although the field of view of augmented reality devices varies greatly in the active area of the glasses, the openness of the design allows for increased stimulation of the true surround, which in turn also reduces VRISE. However, the inability to control the majority of the variables in the environment makes it the least useful format for our current purposes where it is highly desirable to have total control of all aspects of the subject's virtual world. Being able to stimulate the periphery of the patient is extremely valuable in balance therapy as it allows for a more holistic evaluation of the patient’s balance system.
When weighing the advantages of cost and space efficiency, along with the reduction in VRISE symptoms, HMDs are fast becoming a practical choice for many when an immersive environment is desired. With the HMD we have the clinical ability to completely immerse patients in a digital world where we can control every aspect they see and most of what they hear. One example of where this type of total immersed environment is beneficial is the measurement of subjective visual vertical and subjective visual horizontal. Augmented reality systems continue to improve and advance, so in the future new uses for them will undoubtably be found, but for now, VR HMD systems which standardize and control the entire visual stimulus have the most to offer for many types of rehabilitation protocols being developed.
A word about VRISE: Virtual Reality Induced Symptoms and Effects (The Ugly)
VRISE symptoms are one of the most concerning barriers to widespread use and acceptance of virtual reality, especially HMD usage. This is true of many areas of usage, but especially true for the health-related professions, as the symptoms caused by VRISE are often some of the same symptoms that we are trying to remediate. These symptoms often include, but are not limited to, eyestrain, headache, vertigo, nausea, motion or sea sickness, fatigue, and anxiety. At one time these symptoms were reported to cause a 18% drop out rate for HMD usage.(1) Today’s modern HMDs have evolved over the recent years by improving refresh rates, reducing the weight of the device, and allowing the clinician to control other variables. Even though these improvements have greatly reduced some of the VRISE symptomology, the stigma and concerns in some health care populations, especially the elderly, still exist.
It is interesting that many of these improvements in technology are sometimes paradoxical. The gamer wants high resolution, high contrast, brighter and sharper images, and a wider field of view. Unfortunately, studies have shown that the sharper the image, the wider the field of view, the higher the contrast, the greater the VRISE symptoms tend to be. This is particularly true in the populations that most need therapy such as the elderly and those with traumatic brain injuries. (2) However, with good software and savvy clinicians, we can use this to our advantage. We can do this by starting our patient’s therapy protocols with softer focus, a smaller field of view, slower motion, less contrast, and controlling the colors and the brightness. We start the therapy with short intervals and the most comfortable of these settings, gradually increasing the demand as they exhibit improvement.
One very important feature of the HMD device that Bertec has chosen is the “pass through” viewing function. This allows the patient to, at any time, pause the input going to the screens inside the HMD and replace that image with one generated by two cameras showing the real world in front of them. This can easily be switched on and off if the subject feels uncomfortable, has a sense of falling, or just needs a break. Explaining this feature at the beginning may also relieve anxiety and concerns about HMD use.
Key points to remember:
Virtual reality does become the patient’s temporary reality for the time they are immersed, and this can generate post-immersion symptoms that may be intense for 10 minutes after exposure, with milder effects lingering for up to 30 minutes. These post-immersion symptoms do usually reduce with the number of training sessions or usages. From a clinical perspective, it is best to have the patient sit and reacclimate to the surroundings for 10 minutes or until symptoms are gone, before driving or doing other challenging behaviors.
Because a patient’s perceptions and perspectives are often altered from a stroke or traumatic brain injury, we need to help them re-learn or re-set their orientations in space. This is best done with a tightly controlled, multi-sensory approach. An HMD VR system not only allows us to assess and rehabilitate key systems such as vision, vestibular, somatosensory, and cognition, but also helps re-establish normal integration between these key systems.
Because these skills tend to cross over from one discipline to another, the same Bertec HMD protocols may be utilized by a wide variety of clinics or by a wide range of specialties within multi-disciplinary settings. This would include, but not be limited to, OT’s, PT’s, OD’s, MD’s, neuropsychologists, and audiologists.
The wide field of view of the CDP/IVR system compared to an HMD allows for more peripheral visual stimulation and therefore a more holistic evaluation of the patient's balance system.
We invite you to learn more about the HMD and related balance systems.
References:
(1) Sharples, S., Cobb, S., Moody, A., & Wilson, J. R. (2008). Virtual reality induced symptoms and effects (VRISE): Comparison of head mounted display (HMD), desktop and projection display systems. Displays, 29(2), 58-69. https://doi.org/10.1016/j.displa.2007.09.005
(2) Conner, Nathan & Freeman, Hannah & Jones, J. & Luczak, Tony & Carruth, Daniel & Knight, Adam & Chander, Harish. (2022). Virtual Reality Induced Symptoms and Effects: Concerns, Causes, Assessment & Mitigation. Virtual Worlds. 1. 130-146. 10.3390/virtualworlds1020008.
(3) https://www.techtarget.com/whatis/definition/CAVE-Cave-Automatic-Virtual-Environment
