How eye tracking works

Eye tracking, or gaze interaction, is a technology that is used to see where a person is looking on a computer screen. The technology can also be used to control a computer with your eyes instead of using a traditional keyboard and mouse.

Eye tracking, or gaze interaction, is not a new concept, however, only recently has it taken off as a viable solution for helping individuals with physical and cognitive disabilities live richer and more independent lives.

Tobii Dynavox Eye Tracking

How eye tracking works

As a concept, eye tracking is a rather straightforward process.

  1. The eye tracker sends out near infrared light
  2. The light is reflected in your eyes
  3. Those reflections are picked up by the eye tracker’s cameras
  4. Through filtering and calculations the eye tracker knows where you are looking

Model of how eye tracking works

As simple as the concept may be, an enormous amount of research and development has gone into Tobii Dynavox eye trackers to make them work in a simple and unobtrusive way.

Calibrate for better accuracy

In order for eye tracking to work as accurately as possible, the eye tracker must know more about your eyes. This is why you need to do a calibration. During the calibration the eye tracker measures how your eyes reflect light. The calibration is done by following a point, video or other graphic element that moves across the screen. This calibration data is then combined with our unique 3D model of a human eye, and together they give you an optimal eye tracking experience.

Illustration showing eye tracking accuracy and precisions

There are, however, simpler games and applications where accuracy is not as critical, that you can use without performing the calibration. Examples of these would be simple cause and effect games or other apps with big targets that are easy to click.

How to click

There are three ways of clicking when using gaze interaction, and the method available depends on the application you use. The way you choose to click also depends on your abilities.

  • Blink – it is possible to use blinking as a click, but it is not the best way since you loose focus of where you are looking.
  • Dwell – you focus your eyes on a specific area for a predetermined number of milliseconds, and then, a click is performed.
  • Switch – if you are able to control a switch it is often the fastest and most efficient way of clicking. You use your gaze to select where you want to click, and then you press the switch to perform the click.

What makes our trackers unique

There are certain things that set Tobii Dynavox eye trackers apart from others.

You can move your head freely

Tobii eye trackers use a unique and very accurate 3D model of a human eye. This model holds information about the physical shape of an eye and how light is reflected and refracted, among other things. With this model you don’t need to keep your head still when using a Tobii eye tracker, in fact you can move your head freely without any significant loss of precision or accuracy. This is particularly beneficial for individuals with uncontrolled head movement, such as those with Cerebral Palsy or individuals with ALS who might adjust their position throughout the day. 

Works for more or less everyone

For accurate eye tracking, the eye tracker needs to find your pupils*. This can be done through either bright or dark pupil tracking. Bright pupil tracking works similarly to when you get red eyes when using a compact camera with a flash. By placing the flash, or in this case the illuminators, farther away from the lens you can avoid this. This is dark pupil tracking.

Some people track better with dark pupil tracking, others with bright pupil tracking. Factors like pupil size, age and environmental lights affect how well you are tracked using either of the two methods.

Tobii Dynavox eye trackers are unique in that they dynamically switch between bright and dark pupil tracking, so you will always have an optimized eye tracking experience.

Illustration showing reflections

*It is actually the relationship between the pupils and the glints, or reflections, that help the eye tracker determine where you are looking.

How eye tracking leads to a richer and more independent life

There are different uses for eye tracking, or gaze interaction, within the area of assistive technology:

  • Speech generation and communication - individuals who are unable to speak, use their fingers, hands or any other body part in a controlled manor to operate a keyboard, mouse or touch screen can use eye tracking to write messages using only their eyes and then have the computer speak those messages out loud.
  • Computer access – Instead of speaking the messages out loud, they can also be sent via e-mail, chat, SMS or by any other means of long distance communication. In fact, you can access all of the functions of your standard Microsoft tablet or desktop computer through the use of gaze interaction. This makes it possible for many to attend school or stay employed, maintain a hobby, pass time, sharpen skills and more.
  • Environmental control – many appliances, such as TVs, air conditioners and even doors, can be operated by infrared remote controls. Individuals with limited movement, such as those with a spinal cord injury, can use their eye-controlled computer as a remote control and operate appliances via gaze interaction.
  • As a tool for increased engagement – eye tracking can be used as a tool for teachers, parents, assistants and others who work with someone with a disability. With an eye tracker and a simple application like Tobii Dynavox Gaze Viewer, you can see where someone is looking, or not looking on a screen, and base your conversation on this.

Together we are stronger

Even though eye tracking may be a simple concept, it is a very complex and research intense endeavor to make a product that is easy to use.

All of Tobii’s business units use the same core eye tracking technology, but in slightly different ways and for different applications. One of the benefits is that we are able to leverage each other’s strengths and experiences – what our colleagues learn in the field of commercial eye tracking for fast moving consumer goods may also be used within assistive technology – and vice versa.

Since we share a lot of research and development resources, we are also able to keep costs down relative to the performance, quality and the small size of our eye trackers. Few, if any other company within AAC and special needs, can do this.

Eye tracking FAQs

Here are some frequently asked questions about eye tracking and our answers.

How do I click?

  • Dwell – you focus your eyes on a specific area for a predetermined number of milliseconds.
  • Blink – it is possible to use blink as a click, but it is not the best way since you loose focus of where you are looking.
  • Switch – if you are able to control a switch, using that to click is often the fastest and most efficient way of clicking.

Does it work with glasses, contacts, lazy eyes?

Yes, Tobii eye trackers work with most people, regardless if they have glasses, contacts or a lazy eye.

Does eye tracking work outside?

Under certain conditions it may, but when you start to get sunlight and "false" reflections in your eyes, tracking performance may be affected.

Do I have to sit still during calibration?

No, as long as you keep your eyes on the calibration point and have at least one eye within the so called "track box", calibration should be successful.

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