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. Although 50/60 Hz is most common, today many video-based eye trackers run at 240, 350 or even 1000/1250 Hz, which is needed in order to capture the detail of the very rapid eye movements during reading, or during studies of neurology.

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. On average, fixations last for around 200 ms during reading and 350 ms during scene viewing. Preparing a saccade towards a new goal takes around 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.

Contents 1 Usage 2 Commercial eye tracking 2.1 Specific Fields 2.2 Commercial technology 3 References 3.1 Commercial eye tracking 4 External links

[edit] Usage

Eye tracking has many applications:

• 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)

[edit] Commercial eye tracking

In recent years, the increased sophistication and accessibility of eye tracking technologies have generated a great deal of interest in the commercial sector. Applications include web usability, advertising, sponsorship, package design and automotive engineering. In general, commercial eye tracking studies function by presenting a target stimulus to a sample of consumers while an eye tracker is used to record the activity of the eye. Examples of target stimuli may include websites, television programs, sporting events, films, commercials, magazines, newspapers, packages, shelf Displays, consumer systems (ATMs, checkout systems, kiosks), and software. The resulting data can be statistically analyzed and graphically rendered to provide evidence of specific visual patterns. By examining fixations, saccades, pupil dilation, blinks and a variety of other behaviors researchers can determine a great deal about the effectiveness of a given medium or product. While some companies complete this type of research internally, there are many private companies that offer eye tracking services and analysis.

[edit] Specific Fields

The most prominent field of commercial eye tracking research is web usability. While traditional usability techniques are often quite powerful in providing information on clicking and scrolling patterns, eye tracking offers the ability to analyze user interaction between the clicks. This provides valuable insight into which features are the most eye-catching, which features cause confusion and which ones are ignored altogether. Specifically, eye tracking can be used to assess search efficiency, branding, online advertisements, navigation usability, overall design and many other site components. Analyses may target a prototype or competitor site in addition to the main client site.

Eye tracking is commonly used in a variety of different advertising media. Commercials, print ads, online ads and sponsored programs are all conducive to analysis with current eye tracking technology. Analyses focus on visibility of a target product or logo in the context of a magazine, newspaper, website, or televised event. This allows researchers to assess in great detail how often a sample of consumers fixates on the target logo, product or ad. In this way, an advertiser can quantify the success of a given campaign in terms of actual visual attention.

Eye tracking provides package designers with the opportunity to examine the visual behavior of a consumer while interacting with a target package. This may be used to analyze distinctiveness, attractiveness and the tendency of the package to be chosen for purchase. Eye tracking is often utilized while the target product is in the prototype stage. Prototypes are tested against each other and competitors to examine which specific elements are associated with high visibility and appeal.

One of the most promising applications of eye tracking research is in the field of automotive design. Research is currently underway to integrate eye tracking cameras into automobiles. The goal of this endeavor is to provide the vehicle with the capacity to assess in real-time the visual behavior of the driver. The National Highway Traffic Safety Administration (NHTSA) estimates that drowsiness is the primary causal factor in 100,000 police-reported accidents per year. Another NHTSA study suggests that 80% of collisions occur within three seconds of a distraction. By equipping automobiles with the ability to monitor drowsiness, inattention, and cognitive engagement driving safety could be dramatically enhanced.

[edit] Commercial technology

There are two primary components to most eye tracking studies: Statistical analysis and graphic rendering.

These are both based mainly on the amount of visual attention given to specific elements. Statistical analyses generally sum the number of eye data observations that fall in a particular region. Figure 1 provides an example of a GazeStat™ showing the percentage of visual attention that a sample of participants allocated to each feature while viewing a website. This allows for a broad analysis of which site elements received attention and which ones were ignored. Other behaviors such as blinks, saccades and cognitive engagement may also be scrutinized. Statistical comparisons can be made to test competitors, prototypes or subtle changes to a web design. They are also used to compare participants in different demographic groups. The statistical analysis component of an eye tracking study provides objective, quantifiable results that are grounded in systematic experimentation.

In addition to statistical analysis, it is often useful to provide visual depictions of eye tracking results. The simplest method is to create a video of an eye tracking testing session with the gaze of a participant superimposed upon it. This allows one to effectively see through the eyes of the consumer during interaction with a target medium. Examples of such videos can be found in the external links section. Another method graphically depicts the scanpath of a single participant during a given time interval.

The GazeTrace™ in figure 2 shows each fixation and eye movement of a participant during a search on a virtual shelf display of breakfast cereals. Each color represents one second of viewing time, allowing the client to determine the order in which products are seen. Graphics such as these are used as evidence of specific trends in visual behavior. A similar method sums the eye data of multiple participants during a given time interval as a heat map. The GazeSpot™ in figure 3 represents the visual tendencies of several participants, superimposed over a magazine cover. Red and orange spots represent areas of high visual attention. This allows the client to examine which regions in general attract the focus of the consumer. All of these methods are often used in conjunction and incorporated with traditional marketing research measures to produce a comprehensive investigation of commercial value.

[edit] 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.

[edit] Commercial eye tracking

• Chandon, Pierre, J. Wesley Hutchinson, and Scott H. Young (2001), Measuring Value of Point-of-Purchase Marketing with Commercial Eye-Tracking Data. [1]
• Duchowski, A. T., (2002) A Breadth-First Survey of Eye Tracking Applications, 'Behavior Research Methods, Instruments, & Computers (BRMIC),' 34(4), November 2002, pp.455-470.
• National Highway Traffic Safety Administration. (n.d.) Retrieved July 9th, 2006, from [2]
• Weatherhead, James. (2005) Eye on the Future, 'British Computer Society, ITNOW Future of Computing,' 47 (6), pp. 32-33 [3]
• Wittenstein, Jerran. (2006). EyeTracking sees gold in its technology. [Electronic Version]. San Diego Source, The Daily Transcript, April, 3rd, 2006.

[edit] 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