Week 3: Perception and Presence
Virtual, Augmented and Spatial Computing
Week 3
Perception and Presence
Presence is not a property of the technology. It is a property of the experience.
Today’s session
- What is presence?
- Immersion vs presence
- How the brain constructs reality
- Perceptual modalities in XR
- Simulator sickness
- Health effects and mitigation
Why perception matters
XR works by deceiving the perceptual system.
To design effective XR experiences, you need to understand:
- how the brain constructs the experience of being somewhere
- what cues it relies on
- what happens when those cues conflict
Presence
Presence is the subjective feeling of being in a place.
Slater (2009) distinguishes two components:
- Place illusion: the sense of being in the virtual place
- Plausibility illusion: the sense that what is happening is real
Place Illusion
The feeling that you are actually in the virtual environment.
Supported by:
- wide field of view
- head tracking
- spatial audio
- physical scale
Broken by:
- tracking errors
- low frame rate
- visible display edges
Plausibility Illusion
The feeling that the events in the virtual environment are really happening.
Supported by:
- responsive virtual agents
- consistent physics
- cause and effect relationships
Broken by:
- objects passing through each other
- unresponsive environments
- implausible events
Immersion vs Presence
These are often confused but are distinct concepts.
Immersion is an objective property of the technology.
- how much of the sensory field does the system replace?
- how accurately does it track movement?
Presence is a subjective psychological response.
- how much does the user feel they are there?
High immersion tends to support presence but does not guarantee it.
The Reality Trade-off
More immersion is not always better.
Trade-offs include:
- comfort vs presence
- cost vs quality
- portability vs fidelity
Design for the right level of immersion for the task.
Perceptual Modalities
The brain integrates information from multiple sensory systems.
In XR, the most relevant are:
- visual
- auditory
- proprioceptive
- vestibular
- haptic
Visual Perception
The dominant sense in most XR systems.
Key factors:
- stereopsis (depth from two eyes)
- motion parallax (depth from movement)
- accommodation and vergence
- peripheral vision
Auditory Perception
Spatial audio contributes significantly to presence.
The brain uses:
- interaural time difference (ITD)
- interaural level difference (ILD)
- spectral cues from the ear shape (HRTF)
Mismatched audio breaks presence rapidly.
Proprioception
The sense of the position and movement of your own body.
In VR, proprioception can conflict with visual information.
Example: your body feels stationary but your visual system sees movement.
This conflict is a primary cause of simulator sickness.
Vestibular System
The inner ear detects:
- linear acceleration
- rotational acceleration
- gravity
In VR, visual motion without vestibular motion creates conflict.
This is the main cause of vection-induced sickness.
Haptic Perception
The sense of touch and force.
Current XR systems provide limited haptic feedback.
The absence of haptic feedback is a significant limitation for:
- object manipulation
- surface interaction
- social presence
Proximal and Distal Stimuli
Distal stimulus: the actual object or event in the world
Proximal stimulus: the pattern of energy that reaches the sensory receptor
In XR, we manipulate the proximal stimulus to create the perception of a distal stimulus that does not exist.
Simulator Sickness
A form of motion sickness caused by sensory conflict in simulated environments.
Symptoms:
- nausea
- disorientation
- eye strain
- headache
- fatigue
Causes of Simulator Sickness
- Latency: delay between head movement and display update
- Low frame rate: judder and motion blur
- Vection: visual motion without vestibular motion
- FOV mismatch: visual motion at the wrong scale
- Vergence-accommodation conflict
Mitigation Strategies
Design choices that reduce simulator sickness:
- maintain frame rate above 72Hz
- minimise motion-to-photon latency (below 20ms)
- use teleportation instead of smooth locomotion
- add vignette during movement
- allow users to choose comfort settings
- provide rest breaks
Health Effects
Beyond simulator sickness, extended XR use can cause:
- eye strain and fatigue
- neck and shoulder strain
- disorientation after removal
- social isolation
Ethical Considerations
XR designers have a responsibility to:
- disclose health risks
- provide comfort options
- design for accessibility
- avoid exploiting presence for manipulation
Today’s lab
Perception experiments:
- latency manipulation
- scale manipulation
- FOV manipulation
Observe how each affects comfort and presence.
Key questions
- What is the difference between presence and immersion?
- What causes simulator sickness?
- How can design choices mitigate discomfort?
- What ethical responsibilities do XR designers have?
Further reading
- Slater, M. (2009) Place illusion and plausibility
- Jerald, J. (2015) The VR Book, Chapters 4 and 5
- Kolasinski, E. (1995) Simulator sickness in virtual environments
Summary
- Presence is subjective; immersion is objective
- Place illusion and plausibility illusion are distinct
- Multiple perceptual modalities contribute to presence
- Sensory conflict causes simulator sickness
- Design choices can mitigate discomfort
Next week: Input Systems and Interaction Fundamentals