refers to the process of moving from one place to another
This is most commonly used to refer to movement within the virtual environment e.g. how an avatar navigates the virtual world, but can also refer to movement outside of the virtual environment e.g. how the experiencer navigates the real-world while in a virtual experience.
Locomotion mechanics in virtual reality can be broken down into three primary categories:
1. Perambulation
2. Teleportation
3. Transportation
1. Perambulation
Perambulation locomotion methods look to simulate natural ways of moving through a virtual space (without the aid of transport) in real-time. This can include modes of navigation that we would associate with natural human behaviour e.g. walking, crawling, climbing, as well as less natural e.g. flying, swinging.
This locomotion method can be further subcategorised into two types:
i. Kinetic locomotion mechanics
Mechanics that require the expelling of significant kinetic energy through physical movement of the body in order to navigate the avatar through the virtual world.
The primary benefit to this type of mechanic is greater immersion, with the body being engaged - a key contributor to creating a state of embodied presence.
Examples include:
Using the entire body
- Walking around within a pre-defined environment e.g. room-scale VR or VR parks like The Void. A technique called redirected walking can be deployed to trick experiencers into believing they are traversing a seemingly endless virtual world when really they are not.
- Using a specially designed motion platform such as the Virtuix Omni.
Using handheld controllers
- Point and click; where the experiencer points to where they want to move and is then gradually moved towards that destination in real-time (often at a very low speed).
- Grappling; using a grappling hook or similar tool to define a point in the virtual world. This point can then be used as a destination or as an anchor for traversing to other areas e.g. swinging through trees.
- Arm pumping; in order to mirror the motion of jogging.
- Hiking; carrying out a skiing motion with either one or two arms to propel the avatar forward.
- Grab and pull; this is a technique where the experiencer extends their arms and grabs the virtual world in order to pull themselves forward. This is good at simulating climbing.
Using the HMD only
- Head bobbing; where the up and down movement of the head mirrors the motion of jogging.
ii. Artificial locomotion mechanics
Mechanics that utilise buttons, joysticks or D-pads only in order to navigate the avatar through the virtual world.
2. Teleportation
Teleportation locomotion methods look to navigate the experiencer from one point to another without actually traversing the physical space between them. Once actioned, the movement is instantaneous.
Kinetic and artificial mechanic examples include:
- Point and click; where the experiencer points to where they want to move and then instantly materialises in that spot.
- Scouting; where the experiencer can deploy a device (usually thrown) that then relays a view from that new position back to the experiencer. The experiencer can then decide to teleport to that location or not.
- Tunnelling; where the experiencer can temporarily lock their head motion, before a window is overlaid on top of the current view. The movement in the window is then controlled via artificial locomotion method e.g. a joystick.
- Menu selection; where the experiencer uses a menu interface to choose a destination from a list.
- Orienteering; where the experiencer uses a map interface to choose a destination.
3. Transportation
Transportation locomotion methods look to navigate the experiencer from one point to another by means of a vehicle. These vehicles can be representative of the real-world e.g. a bicycle, a car, or entirely fictional e.g. a space ship. They can also be living e.g. a horse or elephant. Typically this involves the experiencer being sat and in a fixed position, but retaining free movement of their limbs.
The experiencer is often placed as either the driver or passenger of the vehicle. By adopting the role of the driver, the experiencer can be given complete or limited control over the vehicle’s movement. As a passenger, the experiencer has no control over the vehicle e.g. being sat on a rollercoaster ride.
This locomotion method can be further subcategorised into two types:
i. Kinetic locomotion mechanics
Mechanics that require the expelling of significant kinetic energy through physical movement of the body in order to navigate the avatar through the virtual world.
Examples include:
- Cycling; using the legs on a bike e.g. VirZoom.
- Arm pumping; like on a handcar.
ii. Artificial locomotion mechanics
Mechanics that utilise buttons, joysticks or D-pads only in order to navigate the avatar through the virtual world.
Challenges of virtual reality locomotion
Immersion
Locomotion in virtual reality can greatly aid a sense of immersion in the virtual world. Two fundamental influencers of this sense of immersion are a) the plausibility of the locomotion mechanic i.e. does the experiencer believe it, does it feel innate, and can the experiencer compare it to a real-world mode of locomotion, and b) how much agency is permitted.
For example, the point and click teleportation mechanic ranks low on plausibility as teleporting isn’t something humans are used to doing in the real-world, but it demands physical engagement from the experiencer meaning it ranks high on agency.
In contrast, the passenger transportation mechanic e.g. a rollercoaster ride, ranks high in terms of plausibility as it is something we can relate back to the real-world, but low in terms of agency as the experiencer is unable to control the speed or destination of the vehicle.
One obvious challenge to any locomotion mechanic that requires physical movement is the experiencer’s health, which can create a significant barrier for entry. Experiencers with physical disabilities, for instance, may be limited to how much of the world they can explore. Similarly, the requirement for physical activity means that at some point the experiencer will run out of energy, which will directly impact the overall duration of the virtual experience and the likelihood of reaching a state of total immersion.
Motion sickness
Striking the perfect balance between plausibility and agency can be difficult without causing motion sickness.
The general consensus is that locomotion that simulates natural movement in a virtual world (usually falling into the perambulation category) without using a kinetic locomotion mechanic will cause motion sickness.
Teleportation and transportation locomotion methods have been shown to significantly decrease motion sickness. Transportation in particular benefits from a grounding effect by placing the experiencer in a contained space e.g. a cockpit where they can anchor themselves to the vehicle. The brain then perceives the movement to be attributed to the vehicle rather than the body.
Recommended Viewing
YouTuber Bumble gives a really helpful demonstration of various different proven and experimental locomotion methods in virtual reality in this video.