The environment can present any number of situations that lead to moments of acceleration and vection. This guide discusses a number of considerations you may want to take into account as you plan your environment, so you can reduce vection as much as possible.
When walking across virtual terrain with either physical or artificial locomotion, the avatar will typically move up and down to follow the surface due to gravity. This can lead to vertical accelerations and vection as the angle of the walking surface varies.
When possible, it is generally advisable to limit movement to flat terrain and avoid the use of slopes and stairs in the accessible environment.
People are most comfortable when they are moving forward. With forward motion, parallax causes points nearest the direction of movement to expand outward more slowly across the retina than points in the periphery. Strafing, back-stepping, spinning and continuous turning movements will often trigger discomfort. Spiral staircases are a good example of something to avoid. When the design allows, plan the environment to minimize the need for extraneous movement.
A textured surface like a wall or ground plane creates more optic flow for the user the closer they walk next to it. When possible, keep the user as far away as possible from large structures and walls without compromising the design. Utilizing open spaces, or large rooms with barriers that prevent getting close to walls can dramatically reduce optic flow as people move through your environment.
Elevators and stairs have the potential to fill the field of view with strong visual motion cues, such as the vertical cascade of horizontal edges created by the steps on a staircase. With elevators, stairs, and other situations where the environment is moving perpendicular to the camera direction, points across the entire field of view are all moving at roughly the same velocity. This creates an even stronger trigger for vection, and is therefore particularly likely to trigger discomfort. The same is true for continuous rotation of the camera viewpoint.
If elevators are necessary, avoid visual design elements that will produce effects that pass the user with each floor such as lights and other details. For stairs, use gentle slopes to maximize the distance from the stairs’ geometry or texture to the camera. Minimize the number of steps to reduce how long people need to be on them, and reduce texture detail as much as possible to limit optic flow.
Even if most of the environment supports free movement through the world, it can be helpful to provide teleport nodes at the top and bottom of stairways. This will allow people who usually prefer to navigate with thumbsticks or other forms of continuous movement the option to avoid the increased comfort risk of the occasional set of stairs. If the design already needs to use short-range teleports to deal with ladders and gaps, adding support for slopes and stairs can be an extension of the same mechanic.
See below for the remaining sections of this guide outlining the many design techniques and best practices to help inspire and inform your next VR locomotion system.