Eye tracking: Difference between revisions
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While its integration into consumer VR/AR is relatively recent, the systematic study of eye movements dates back to the 19th century. [[Louis Émile Javal]] noted in 1879 that reading involved discrete stops (fixations) and rapid movements (saccades).<ref name="Rayner1998">Rayner, K. (1998). Eye movements in reading and information processing: 20 years of research. *Psychological Bulletin, 124*(3), 372–422.</ref> Early tracking devices included [[Edmund Huey]]'s contact lens-based tracker (~1908)<ref name="Huey1908">Huey, E.B. (1908). *The Psychology and Pedagogy of Reading*. Macmillan.</ref> and [[Guy Thomas Buswell]]'s film-based systems in the 1930s. [[Alfred L. Yarbus]]'s work in the 1960s highlighted how viewing patterns are task-dependent.<ref name="Yarbus1967">Yarbus, A.L. (1967). *Eye Movements and Vision*. Plenum Press.</ref> These foundational efforts paved the way for modern video-based and integrated tracking systems. | While its integration into consumer VR/AR is relatively recent, the systematic study of eye movements dates back to the 19th century. [[Louis Émile Javal]] noted in 1879 that reading involved discrete stops (fixations) and rapid movements (saccades).<ref name="Rayner1998">Rayner, K. (1998). Eye movements in reading and information processing: 20 years of research. *Psychological Bulletin, 124*(3), 372–422.</ref> Early tracking devices included [[Edmund Huey]]'s contact lens-based tracker (~1908)<ref name="Huey1908">Huey, E.B. (1908). *The Psychology and Pedagogy of Reading*. Macmillan.</ref> and [[Guy Thomas Buswell]]'s film-based systems in the 1930s. [[Alfred L. Yarbus]]'s work in the 1960s highlighted how viewing patterns are task-dependent.<ref name="Yarbus1967">Yarbus, A.L. (1967). *Eye Movements and Vision*. Plenum Press.</ref> These foundational efforts paved the way for modern video-based and integrated tracking systems. | ||
== Technical Principles == | ==Technical Principles== | ||
=== Tracking | ===Tracking Method=== | ||
Most eye tracking systems in contemporary VR and AR headsets employ one of several core technologies: | Most eye tracking systems in contemporary VR and AR headsets employ one of several core technologies: | ||
* | *'''[[Pupil Center Corneal Reflection]] (PCCR)''': This is the predominant method. It involves:<ref name="Holmqvist2011">Holmqvist, K., Nyström, M., Andersson, R., Dewhurst, R., Jarodzka, H., & Van de Weijer, J. (2011). *Eye tracking: A comprehensive guide to methods and measures*. Oxford University Press.</ref><ref name="RoadToVREyeTracking">Lang, B. (2021, July 21). *Casual Explainer: What is Eye-tracking & How Does it Work?* Road to VR. https://www.roadtovr.com/casual-explainer-what-is-eye-tracking-how-does-it-work/</ref> | ||
*'''Illumination:''' [[Infrared]] (IR) light-emitting diodes ([[LED]]s) safely illuminate the eye. IR light is used because it is invisible to the human eye, preventing distraction, and provides high contrast for [[camera]]s. | |||
*'''Imaging:''' Small, high-[[frame rate]] infrared cameras capture images of the eye, specifically tracking the center of the [[pupil]] and the reflection(s) of the IR light off the surface of the [[cornea]] (known as glints). | |||
*'''[[Algorithm|Algorithmic Processing]]:''' Sophisticated [[computer vision]] and [[image processing]] algorithms analyze the captured images. By calculating the vector between the pupil center and the corneal reflection(s), the system determines the eye's orientation and calculates the user's gaze point with high accuracy. | |||
*'''[[Calibration]]:''' A per-user calibration process is usually required upon first use, and sometimes periodically, to account for individual differences in eye physiology (e.g., corneal shape, pupil size range) and the precise fit of the headset. This typically involves the user looking at specific points displayed within the headset. | |||
* | *'''Video-based eye tracking (Shape/Feature Tracking)''': Uses cameras aimed at the eyes to capture images, which are then analyzed using computer vision algorithms to identify eye features (pupil outline, iris texture, blood vessels) to determine gaze direction without necessarily relying on corneal reflections.<ref name="Hansen2010">Hansen, D. W., & Ji, Q. (2010). In the eye of the beholder: A survey of models for eyes and gaze. *IEEE Transactions on Pattern Analysis and Machine Intelligence, 32*(3), 478-500.</ref> PCCR is often considered a subset of this broader category. | ||
* | *'''[[Electrooculography]] (EOG)''': Measures the electrical potential difference between electrodes placed on the skin around the eyes. This potential changes predictably as the eye rotates. While less common for high-accuracy gaze pointing in consumer VR/AR due to lower precision and susceptibility to muscle noise, it can be used for detecting larger eye movements or in specialized applications.<ref name="Bulling2011">Bulling, A., Ward, J. A., Gellersen, H., & Tröster, G. (2011). Eye movement analysis for activity recognition using electrooculography. *IEEE Transactions on Pattern Analysis and Machine Intelligence, 33*(4), 741-753.</ref> | ||
* | *'''[[Scleral search coil]]''': Involves wearing a special contact lens containing a wire coil. The user sits within a magnetic field, and eye movements induce currents in the coil, providing extremely precise measurements. This is highly invasive and primarily used in laboratory research, not consumer VR/AR.<ref name="Robinson1963">Robinson, D.A. (1963). A method of measuring eye movement using a scleral search coil in a magnetic field. *IEEE Transactions on Biomedical Engineering, BME-10*(4), 137–145.</ref> | ||
=== Key Components (PCCR-based) === | ===Key Components (PCCR-based)=== | ||
A typical PCCR eye tracking system integrated into a VR/AR headset consists of: | A typical PCCR eye tracking system integrated into a VR/AR headset consists of: | ||
* | *'''Illuminators''': Infrared LEDs providing consistent, non-visible lighting. | ||
* | *'''Cameras''': Specialized high-speed infrared cameras positioned to capture clear images of both eyes. | ||
* | *'''Processing Unit''': Either onboard [[System on a Chip|SoC]] resources or dedicated hardware to run the detection and gaze calculation algorithms in real-time. | ||
* | *'''Calibration Software''': [[Software]] routines guiding the user through calibration and storing individual profiles.<ref name="Kar2017">Kar, A., & Corcoran, P. (2017). A review and analysis of eye-gaze estimation systems, algorithms and performance evaluation methods in consumer platforms. *IEEE Access, 5*, 16495-16519.</ref> | ||
=== Eye Movement Types Measured === | ===Eye Movement Types Measured=== | ||
Eye tracking systems in VR/AR can detect and analyze various types of eye movements and states: | Eye tracking systems in VR/AR can detect and analyze various types of eye movements and states: | ||
* | *'''[[Fixations]]''': Periods when the gaze remains relatively stable on a specific area (typically > 100-200 ms), indicating visual attention. | ||
* | *'''[[Saccades]]''': Rapid, ballistic movements shifting the gaze between fixation points (typically 30-120 ms). | ||
* | *'''[[Smooth pursuit]]''': Movements allowing the eyes to smoothly follow a moving object. | ||
* | *'''[[Vergence]]''': The simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision, critical for focusing on objects at different depths. | ||
* | *'''[[Pupil dilation|Pupil Size / Dilation]]''': Changes in pupil diameter (pupillometry), which can correlate with changes in light levels, cognitive load, emotional arousal, or interest.<ref name="Leigh2015">Leigh, R. J., & Zee, D. S. (2015). *The neurology of eye movements*. Oxford University Press.</ref> | ||
* | *'''Blinks''': Detection of eyelid closures. | ||
== Applications in VR and AR == | == Applications in VR and AR == | ||