Everything you always wanted to know about eye tracking (Part 1)

Written by on October 17, 2016 in Features with 0 Comments

eye-tracking-e1480003857477Eye 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 article is packed with all the need-to-knows and useful tools to help you get a solid grasp of eye tracking technology and best practices.

The technology behind eye tracking

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.

Modern day eye trackers

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.

visible_light_eye-tracking_algorithm

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.

Remote and mobile eye tracking

There are two types of eye tracker: Remote (also called screen-based or desktop) and head-mounted (also called mobile).

Remote eye trackers

remote-eye-tracking-e1457083472356

  • Record eye movements at a distance (no attachments to respondent)
  • Mounted below or placed close to a computer or screen
  • Respondent is seated in front of eye tracker
  • Recommended for observations of any screen-based stimulus material in lab settings such as pictures, videos, and websites, offline stimuli (magazines, books etc.), and other small settings (small shelf studies etc.)

Head-mounted eye trackers

head-mounted-eye-tracking-e1457083489998

  • Record eye activity from a close range
  • Mounted onto lightweight eyeglass frames
  • Respondent is able to walk around freely
  • Recommended for observations of objects and task performance in any real-life or virtual environments (usability studies, product testing etc.)

Who uses eye tracking?

Not to spoil your anticipation, but you may be surprised to discover that eye tracking is not exactly a novelty as such – in fact, it has been around for many years in psychological research.

Given the tight relationship between eye movements and human cognition, it makes intuitive sense to utilize eye tracking as experimental method to gain insight into eye movement-related brain activity. You can see a umber of examples here.

In the following article in this series we will take a look at who exactly uses eye tracking and why? We will also have a look at the most common applications in academic and commercial research.

eye-tracking-infographic

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