5.1 Head-mounted displays (HMDs) for VR

Head-mounted displays are the cornerstone of virtual reality experiences. These devices use stereoscopic displays and specialized lenses to create immersive 3D environments, tricking our brains into perceiving depth and presence in virtual worlds.

HMDs come in various forms, from tethered systems connected to powerful computers to standalone units with built-in processing. Key factors like display technology, ergonomics, and motion tracking all impact the overall VR experience and user comfort.

Display Technology

Stereoscopic Displays and Lenses

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  Stereo Displays – Introduction to Sensation and Perception View original

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• Stereoscopic displays create depth perception by presenting slightly different images to each eye
  • Mimics how human eyes perceive depth in the real world
  • Requires precise alignment and timing of the two images to avoid discomfort or visual artifacts
• Fresnel lenses are commonly used in VR headsets to magnify and focus the display for each eye
  • Consist of a series of concentric rings with different curvatures to reduce the overall thickness and weight compared to traditional lenses
  • Help to expand the field of view and create a more immersive experience

OLED vs LCD Displays

• OLED (Organic Light-Emitting Diode) displays offer several advantages for VR headsets compared to LCD (Liquid Crystal Display) screens
  • OLED displays have faster response times, reducing motion blur and improving the overall visual experience
  • Provide deeper blacks and higher contrast ratios, enhancing the sense of immersion
  • Can be more power-efficient, especially when displaying dark scenes
• LCD displays are still used in some VR headsets due to their lower cost and higher pixel density
  • Tend to have better color accuracy and longer lifespan compared to OLED displays
  • May suffer from slower response times and reduced contrast ratios

Ergonomics and Comfort

Head-Mounted Display (HMD) Design

• HMD design plays a crucial role in user comfort and experience
  • Weight distribution should be balanced to reduce neck strain and fatigue
  • Adjustable straps and padding ensure a secure and comfortable fit for various head sizes and shapes
  • Ventilation and airflow considerations help prevent lens fogging and minimize heat buildup
• Interpupillary distance (IPD) adjustment allows users to align the lenses with their eyes for optimal clarity and comfort
  • IPD is the distance between the centers of the pupils and varies among individuals
  • Misaligned IPD can lead to eye strain, blurred vision, and headaches

Tethered vs Standalone HMDs

• Tethered HMDs are connected to a computer or gaming console via cables
  • Offer higher graphical fidelity and processing power, as the headset relies on the connected device for rendering
  • Require a dedicated space and limit user mobility due to the cable connection
  • Examples include Oculus Rift and HTC Vive
• Standalone HMDs have built-in processing units and batteries, allowing for untethered use
  • Provide greater freedom of movement and portability, as users are not restricted by cables
  • May have lower graphical quality and processing power compared to tethered HMDs due to hardware limitations
  • Examples include Oculus Quest and Pico Neo

Performance Factors

Latency and Motion Tracking

• Latency refers to the delay between user input and the corresponding visual feedback in the VR headset
  • Low latency is essential for maintaining immersion and preventing motion sickness
  • High latency can cause a disconnect between the user's actions and the virtual environment, leading to discomfort and disorientation
• Motion tracking systems capture the user's head and body movements to accurately reflect them in the virtual world
  • 6 Degrees of Freedom (6DoF) tracking allows for both rotational and translational movement, providing a more natural and immersive experience
  • Accurate motion tracking minimizes latency and ensures smooth, responsive gameplay or simulations
• Techniques such as asynchronous timewarp and reprojection help reduce perceived latency by warping the rendered image based on the most recent head tracking data
  • Compensates for the time difference between rendering frames and displaying them on the headset
  • Helps maintain a smooth and stable visual experience, even when the rendering performance drops below the target frame rate