Eye tracking
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Eye tracking is a technique used in cognitive science, psychology (notably psycholinguistics), human-computer interaction (HCI), marketing research, medical research, and other areas. The most widely used current designs are video based eye trackers. A camera focuses on one or both eyes and records their movement as the viewer looks at some kind of stimulus. Most modern eye-trackers use contrast to locate the center of the pupil and use infrared and near-infrared non-collumnated light to create a corneal reflection (CR). The vector between these two features can be used to compute gaze intersection with a surface after a simple calibration for an individual.
Two general types of eye tracking techniques are used, Bright Pupil and Dark Pupil. The difference between the two is based on the location of the illumination source with respect to the optics. If the illumination is coaxial with the optical path then the eye acts as a retroreflector as the light reflects off the retina creating a bright pupil effect similar to red eye. If the illumination source is offset from the optical path, then the pupil appears dark.
Bright Pupil tracking creates greater iris/pupil contrast allowing for more robust eye tracking with all iris pigmentation and greatly reduces interference caused by eyelashes and other obscuring features. It also allows for tracking in lighting conditions ranging from total darkness to very bright. However, bright pupil techniques are not effective for tracking outdoors as extraneous IR sources interfere with monitoring.
Eye tracking setups vary greatly; some are head-mounted, some require the head to be stable (for example, with a chin rest), and some function remotely and automatically track the head during motion. Most use a sampling rate of at least 30Hz, though 50/60 Hz is more common, in order to capture the detail of the very rapid eye movements.
Eye movements are typically divided into fixations and saccades, when the eye gaze pauses in a certain position, and when it moves to another position, respectively. The resulting series of fixations and saccades is called a scanpath. Most information from the eye is made available during a fixation, but not during a saccade. The central one or two degrees of the visual angle (the fovea) provide the bulk of visual information; the input from larger eccentricities (the periphery) is less informative. Hence, the locations of fixations along a scanpath show what information loci on the stimulus were processed during an eye tracking session. Most people cannot make a conscious saccade in less than 200 milliseconds.
Scanpaths are useful for analyzing cognitive intent, interest, and salience. Other biological factors (some as simple as gender) may affect the scanpath as well. Eye tracking in HCI typically investigates the scanpath for usability purposes, or as a method of input in gaze-contingent displays or gaze-based interfaces.
Usage
Eye tracking has many applications [link]:- Cognitive Studies
- Medical Research
- Human Factors
- Computer Usability
- Vehicle Simulators
- In-vehicle Research
- Training Simulators
- Virtual Reality
- Adult Research
- Infant Research
- Adolescent Research
- Geriatric Research
- Primate Research
- Sports Training
- fMRI / MEG / EEG
- Commercial eye tracking (web usability, advertising, marketing, automotive, etc)
References
Rayner, K. (1998) Eye movements in reading and information processing: 20 years of research. Psychological Bulletin, 124, 372-422.Duchowski, A. T., "A Breadth-First Survey of Eye Tracking Applications", Behavior Research Methods, Instruments, & Computers (BRMIC), 34(4), November 2002, pp.455-470.
Jacob, R. J. K. & Karn, K. S. (2003). Eye Tracking in Human-Computer Interaction and Usability Research: Ready to Deliver the Promises. In R. Radach, J. Hyona, & H. Deubel (eds.), The mind's eye: cognitive and applied aspects of eye movement research (pp.573-605). Boston: North-Holland/Elsevier.
See also
- [Video of website usability testing using a Tobii 1750 Eye Tracking monitor (from SimpleUsability Ltd)]
- [Video demonstration of Eye Tracking in action (from Etre.com)]
- Eye tracker
- * [link] AVI movie: Eye blink followed by saccade with dynamic overshoot, measured at 1250Hz sampling rate (slow motion replay, measured with SMI iViewX HS1250)
- * [link] AVI movie: Recording of binocular torsional nystagmus elicited by head tilting (measured with SMI 3D VOG)
External links
- [Introduction to Eyetracking: Seeing Through Your Users' Eyes] Introduction to eye tracking basics + usability studies and natural interaction
- [Eyetrack III] study of how user's eyes track a web page
- [Eyetracking study of how people read online]
- [eyetools] study of how user's track a web page
- [Vestibular Research Lab] vestibular research lab at Charité - Universitätsmedizin Berlin, Campus Benjamin Franklin
- [EServer TC Library: Eye Tracking]
- [Chronos Vision GmbH] Chronos Vision offers high speed machine systems and eye tracking devices.
- [Eye tracking Research and Applications Website]
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