Eye Tracking 101: How Does It Work?

image showing how eye tracking works: Near-infrared light is directed toward the center of the eyes (pupil) causing visible reflections in the cornea (outer-most optical element of the eye), which are tracked by a camera.

Eye tracking is about where we look, what we look at, how much time we spend looking at it, how our pupils react to different kinds of visual stimulation and when we blink.

Put most simply, eye tracking refers to the measurement of eye activity. More specifically, eye tracking implies the recording of eye position (point of gaze) and movement on a 2D screen or in 3D environments based on the optical tracking of corneal reflections to assess visual attention. While the idea of eye tracking is quite straightforward, the technology behind it might strike you as rather complex and inscrutable.

No need to hit the panic button. The following pages are packed with all the need-to-knows and useful tools to help you get a solid grasp of eye tracking technology and best practices.

How exactly does eye tracking work?

Eye tracking on the rise. While early devices were highly obtrusive and involved unduly cumbersome procedures, eye trackers have undergone quite a technological revolution in recent years. Long gone are the rigid experimental setups and seating arrangements you might think of.

Modern eye trackers are hardly any larger than smart phones and provide an extremely natural experience for respondents. Remote, non-intrusive methods now render eye tracking an easy to use, accessible tool in human behavior research that allows to objectively measure eye movements in real-time.

The technology behind eye tracking

Most modern eye trackers utilize near-infrared technology along with a high-resolution camera (or other optical sensor) to track gaze direction. The underlying concept, commonly referred to as Pupil Center Corneal Reflection (PCCR), is actually rather simple. The math behind it is …well, a bit more complex. We won‘t bore you with the nature of algorithms at this point.

Here‘s the bottom line of how it works: Near-infrared light is directed toward the center of the eyes (pupil) causing visible reflections in the cornea (outer-most optical element of the eye), which are tracked by a camera.

image showing how eye tracking works: Near-infrared light is directed toward the 	center of the eyes (pupil) causing visible reflections in the cornea (outer-most optical element of the eye), which are tracked by a camera.

Why infrared spectrum imaging?

Fair enough to ask. Let‘s see why visible imaging spectrum holds difficulties and should only be second choice in eye tracking technology.

The accuracy of eye movement measurement heavily relies on a clear demarcation of the pupil and detection of corneal reflection. While the visible spectrum is likely to generate uncontrolled specular reflection, illuminating the eye with infrared light, which is not perceivable by the human eye, renders the demarcation of the pupil and the iris an easy task – while the light directly enters the pupil, it just “bounces off” the iris.

Here is an overview of eye tracking in an infographic with some really interesting facts.

eye tracking infographic

The contents of this post appeared first on the iMotions blog. Head there to learn more about eye tracking and everything related to it.

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