Appropriate use of Virtual Reality Headsets, Philippe Fuchs
The latest publication from Professor Philippe Fuchs is the ultimate guide on best practices for designing VR. An uncompromised toolbox for hardware, software developers, storytellers and VR enthusiasts.
Author : Philippe Fuchs, Mines ParisTech
Published by World VR Forum
Publication date : May, 2016
Print length : 171 pages
Format : A5
Type of product : Scientific literature
The use of virtual reality headsets (referred to as VR headsets or Head Mounted Displays) can trigger a number of health and comfort issues, which are mainly caused by certain categories of virtual reality (VR) applications, and make users feel unwell primarily as a result of:
- sensorimotor discrepancies, including those due to excessively long latency times;
- the psychological activity of the disturbed subject in the virtual environment (VE);
- poor interfacing between the subject’s visual system and the VR headset;
- and unsafe technological devices.
Virtual reality techniques almost always induce discrepancies, either within one of the senses (for example, a discrepancy between the accommodation and convergence of the eyes for stereoscopic vision which we will explain in detail in this article), between several senses (e.g. locomotion on a treadmill resulting in a discrepancy between the vision and vestibular systems), or between the senses and motor responses (when manipulating virtual objects without force feedback, meaning users have no sensation of their weight, for instance). In the real world, man builds a coherent representation based on all the sensory stimuli received. In the virtual world, users will therefore seek to interpret coherently what they perceive based on their experience in the real world, despite these sensorimotor discrepancies. However, it is currently hard to determine whether the subject immersed in a given virtual environment is able to perceive and make sense of these environments effortlessly, by managing to overcome such sensorimotor discrepancies.
In virtual environments, another potential discomfort for users is the slowness of the reactions in the VE in relation to the actions they have taken. This latency lag, which depends on the technological performance of the VR device, will therefore affect the behaviour of users. It can be described as a sensorimotor discrepancy, but one with a temporal criterion.
However, independently of the technical solutions used, and even when using a perfect VR headset – i.e. one that offers the same visual quality as that of the real world – a discrepancy will always be present for certain types of applications. The aim is not merely to resolve technological issues in the near future to eliminate all such discrepancies and allow users to perform any sensorimotor activity in a virtual environment, as some limitations will always be encountered. In principle, we are creating a new artificial world with its rules, limitations and potentialities, some of which will exceed or differ from those encountered in the real world.
Based on experience and some classic and well-analysed cases we are well aware that people are able to overcome some discrepancies by adjusting to them. And some adjustments occur almost naturally: the most explicit example is the virtual motion in front of a small computer screen or games console. Despite this discrepancy between visual-vestibular cues, users will still perceive the Real Environment (RE) in their peripheral vision and to some extent will experience the sensation of their own movement, if the virtual environment (VE) displays moving images. The phenomenon of vection is responsible for this sensation of movement, despite the fact that the vestibular systems of the person who is motionless in the real world are not detecting any movements. It is extremely rare to find people who do not adjust to this type of virtual movement in front of a screen that does not cover their peripheral vision. For observations via a VR headset, the problem is much more complex, as we will describe in the following paragraphs.
In VR applications, not all of our senses intervene to create the desired simulation. However, some are to be taken into account for the sensorimotor discrepancies induced by VR techniques, such as:
- skin sensitivity;
- the kinaesthetic sense (vestibular systems, sensory receptors in the joints, etc.);
- muscle proprioception.
Most tissues in the human body (muscles, skin, joints, tendons, etc.) have receivers that can be activated mechanically. Their sensory stimuli are divided into two groups: skin sensitivity and proprioception (internal sensitivity). Skin sensitivity comprises touch, as well as sensitivity to pressure, vibration and temperature.
Proprioception relates to three areas: namely, sensitivity to spatial positioning, body movements and the forces exerted on the muscles: The first two areas correspond to the kinaesthetic sense, and the last to muscle proprioception. An awareness of movement is given by the position of the different parts of the body and their relative mobility, as well as by the force of muscular contractions during the movement. In addition to the proprioceptive organs of the muscles, tendons and joints, the organs that provide the sensation of motion are those located in the receptors of both vestibular systems in the inner ears as well as, to a large extent, the vision. Chapter 3 of the book entitled “Virtual Reality: Concepts and Technologies” offers a detailed presentation of the human senses.
The latency time (or simply latency) is the time lag between the user’s action, its processing by a computer and the corresponding response displayed in the VR headset.
With natural vision, eyes accommodate and converge on the same point in space, therefore at the same distance from the head, which is not the case with artificial (stereoscopic) vision.
Stereoscopic images: a pair of two different images, each seen by one of the observer’s eyes.
Vestibular systems perceive acceleration and tilting of the head through sensory receptors (otoliths and semicircular canals) in both inner ears.
As their peripheral vision is in the real environment, the posture of users in the RE remains stable due to the coherence between their peripheral vision and vestibular systems, and they do not experience any sensations of sickness or discomfort.