Methods of Eye-Tracking

My team’s project involves adapting eye-tracking as a way for Mark to use his computer at work. In this post I’ll give a whirlwind overview of the various applications and methods of eye-tracking.

What is eye-tracking? Eye-tracking is the collection of data about the rotation of the eyeball within the socket. Most often, we are interested in where the gaze of the eye rests on a page or on a screen. This data can be used for many purposes.

Eye-tracking data can be used to study human perception and cognition. For example, a recent trend in web usability studies involves taking into account the pattern of a user’s gaze while navigating a website. In addition, marketers may use eye-tracking to study where the most effective advertisement placement is.

Heat map of eye gaze on Google search results

Heat map of eye gaze on Google search results

More recently, technology developers have explored using eye-tracking as a means of human-computer interaction. This is where assistive technologies come into play: eye-tracking provides a means of interacting with the computer–of controlling the cursor and entering in keypresses–for users who cannot use a mouse or keyboard.

Tobii eye-tracker

Tobii EyeX, the commercial eye-tracker we are using

There are three main categories of eye-tracking methods that have been found. The first involves attaching a physical object to the eye. This was the first method to be developed, in the early 1900s, by an educational psychologist named Edmund Huey. Huey’s device consisted of a contact lens, with a hole for the pupil, connected to a small aluminum rod. This method has the advantage of being very accurate, but the disadvantage of being physically intrusive.

The second category consists of measuring reflection of light, whether infrared or visible light, across the eye. Specifically, a camera measures reflection of light from the cornea and then performs video computation to find the eye gaze. This method has the advantage of being low-cost and un-intrusive, but the disadvantage of being less accurate and highly sensitive to lighting conditions.

Finally, the third category involves placing electrodes around the eyes and measuring the electric field of the eyes. As the eye rotates, the electric field changes. Unlike the other two methods, the eye gaze can be measured in this fashion even when the eyes are closed; this is its most salient advantage. However, a disadvantage of this method is that it requires wearing a device and a lot of setup.

Man with electrodes placed on face

Eye-tracking with electrodes

For our project with Mark, we’re using Tobii EyeX, an eye-tracker originally intended for use in gaming applications. We chose to go with the second method of eye-tracking, as it is the only option that is non-intrusive and does not require attachment of any device to the body. Our project is the continuation of a century’s history of making eye-tracking devices ever more useful and usable.

One Response to “Methods of Eye-Tracking”

  1. Jeff Dusek says:

    Great post, thanks for providing a concise background on different eye tracking methods. The use of eye tracking to optimize webpage layout and ad placement is something I hadn’t thought about, but makes a lot of sense. Do you know if Google or other web platforms are actively using these techniques.

    In the future, consider embedding some videos or additional images in your posts. In this case I think videos demonstrating the different eye tracking methods would have been very helpful.

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