Eye tracking: what is it, what types are there and what is it for?

It is said that the eyes are the window of the soul, but, also, they allow us to know the way in which we look at the details of a painting, the parts of our body that we look at the most when we are in front of the mirror or what catches our attention from a ad.

Eye Tracking, or ocular tracking, is a process in which the movements of the eyes are measured, in order to determine where, what and for how long a person is looking.

The eyes are, perhaps, the most important organs through which we obtain information about the world and, for this reason, eye tracking techniques have become very important in investigation. Let's take a closer look at these techniques.

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What is Eye Tracking?

The "Eye Tracking", also known as ocular tracking, refers to the set of techniques that allow evaluating where a person is looking, what particular object or detail you focus on and how long you keep your gaze fixed. The devices that carry out this technique are called “eye trackers”, and are made up of multiple different types of devices that allow you to fixate on the angle of the gaze or the movement of the eye in Yes.

Eye tracking techniques They have been used in research in different fields, such as cognitive linguistics, psychology and, also, marketing and product design. They are techniques that allow knowing the visual behavior of a person, be it subject, patient or buyer, and based on to this draw conclusions about what your interests are, your emotional state or even if you have some kind of pathology.

Story

Although nowadays eye tracking techniques use modern devices that allow recording the movement of the eyes or the direction of the eye. look, the truth is that the first attempts to know where people were looking when doing a certain type of task date back to the century XIX. These early attempts were made by direct observation of where the subject was looking, and what kind of information or striking stimulus had been presented to him in his visual field.

Louis Emile Javal, in 1879 it was observed that, when reading, the reading process did not involve a gentle sweep of the eyes throughout the text. Until then it was believed that, when reading, for example, a book, each line was followed from beginning to end, without jumping or getting "stuck" for a few seconds in the same word. Javal observed that the reading was actually a series of short stops, fixations, and quick saccades.

During the 20th century, an attempt was made to solve several questions about reading, such as what were the words in which they stopped the most, how much time was spent on them or how and why they went back and read words again read. Edmund Huey, with the intention of solving these questions, designed a contact lens with a hole that was placed directly on the participant's eyes. With these lenses he could register, very precisely, the movement of the eyes when he was reading, and what he was looking at.

Given the Huey's technique was, despite being objective and effective, quite annoying and invasive, other researchers invented their own “eye trackers”, which were limited to accurately recording eye movement without the need to introduce anything into the participant's eye. One of them, Guy Thomas Buswell, was the one who devised the first non-invasive eye tracking device, using light beams reflected in the eye and that, when the eyeball moved, the light beam was deflected, recording the process in a movie.

During the 1950s and 1960s it would be discovered that eye movement, both in front of a text as an image, could be conditioned by the task that the participant had to perform, or their interests. This was the case in the investigations of Alfred L. Yarbus, who came to the conclusion that eye movement did not depend solely on what was in front of the subject, but also influenced what he expected to find.

Today, eye tracking devices have been improved and become much more accurate and less invasive. They have been adapted not only to know the visual behavior of people in front of a painting, a page of text or a face, knowing what people pay more attention to. Since the 2000s eye tracking devices have been manufactured for people with motor disabilities, which interpret eye movements as commands, causing, for example, the wheelchair to move or a sentence to be emitted by looking at the words on a screen.

Types of eye trackers

Although today most eye trackers are non-invasive and use video recording, they are not the only ones, nor are they, strictly speaking, the most accurate. Next we will see the three main types of eye tracking.

1. Invasive sensing

You use something that is attached to the eye, such as a contact lens with a built-in mirror. This type of eye tracking is quite invasive, as its name suggests, since it implies placing something in the subject's eye that moves according to how the eyeball does.

As the eyes are delicate organs and, as a rule, people are very sensitive to being touched, there are few times in which the participant refuses to be placed with an invasive sensing eye tracker. It is quite an annoying technique.

But despite being annoying, eye trackers of this type have the advantage that they allow the movement of the eye to be registered quite accurately, since they move according to how it does. The recordings obtained through this system are very detailed.

2. Non-invasive sensing

This monitoring is done without the need for direct contact with the eye. Through a light, such as infrared, eye movement is known through the reflection of the light beam, which is captured by a video camera or an optical sensor.

Non-invasive sensing eye trackers they usually use the corneal reflex and the center of the pupil to know the movement of the eyeball. Others also use the front of the cornea and the back of the lens. There are also those that record the inside of the eye, noting the position of the blood vessels in the retina.

In general, optical methods are well regarded in the field of research, since they are low cost and non-invasive.

However, they may fail to record eye movement, since sometimes they don't accurately detect the pupil, cornea, or whatever eye cues they use to do the eye tracking. Furthermore, if the subject closes his eyes, her visual behavior cannot be registered.

Some virtual reality devices, such as FOVE glasses, have eye trackers of this type, allowing us to know where the person is looking once immersed in the virtual environment.

3. Electrical potentials

A quite special eye tracking technique is the one that uses electrical potentials, measured with electrodes placed around the eyes.

The eyes are the origin of an electric potential field, which can be measured even with the eyes closed.. The electrodes can be positioned in such a way as to generate a dipole, a positive pole on the cornea, and a negative pole on the retina.

The electrical signal obtained from this technique is called an electrooculogram (EOG). If the eyes move from the center to the periphery, the retina approaches one of the electrodes, while the cornea approaches the opposite.

The main advantage of eye tracking using electrical potentials is that is able to record eye movement even with the eyelids closed, since the eye's magnetic field is being recorded.

However, its main disadvantage is that, although it is not completely invasive, it involves having to place electrodes, something that implies having to scratch the subject's skin a bit. In addition, the care of these electrodes is quite delicate, and they can fail very easily or not conduct the current well depending on the skin of the subject.

Eye Tracking Applications

Eye tracking has proven quite useful for various fields, both theoretical and practical.

Marketing and web design

In marketing, eye tracking is a useful technique since it allows to know the visual patterns of the buyers, to know what details in an advertisement, whether on television, in newspapers or on the web, they pay more attention.

Thanks to this, companies can make quantitative studies of how communication, that is, their ads, are perceived in the population, and how to improve it. Also it is possible to know the impact of audiovisual advertising, both in a neutral context, that is, experimental, and in life itself.

By knowing what details users pay more attention to, it is possible to improve company web pages to make them more attractive and manageable for potential buyers, in addition to managing to keep their attention and direct them towards the purchase of the product or service.

But not only eye tracking focuses on how to advertise products, but also in how they should be packaged. With eye tracking, it is possible to see towards which stimuli of a certain color, shape or various visual characteristics the subject pays the most attention. In this way, companies can design their products and their packaging to induce purchase.

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People with disabilities

Eye tracking has the great advantage of being able to help people with reduced mobility, such as people with tetraplegia or cerebral palsy.

Non-invasive sensing eye tracking can be combined with computer screens, in which letters appear that the user can look at. By fixing its gaze on those letters, a device forms words and phrases that sound through a loudspeaker, allowing people with speech problems to communicate.

Also You can do the same to get the wheelchair to move. The person fixes his gaze on the screen, on which arrows appear indicating the direction. Fixing his gaze on each of these arrows, he sends the command to the mechanized wheelchair to move in the desired direction.

Psychology

Studying visual behavior it is possible to know if a person manifests some type of pathology, or in what way their way of looking at things differs from what is expected in a person without a diagnosis psychopathological.

It has been observed that people with attention deficit hyperactivity disorder look far more easily decentered than people without the diagnosis.

This means that they do not pay due attention to elements such as the class blackboard or the textbook, encouraging learning and understanding problems that can be mistaken, in the most severe cases, for dyslexia or even delay mental.

It should be said that eye-tracking techniques can be very useful to diagnose both ADHD and dyslexia because, although in both there are problems of reading, the pattern of visual behavior differs, with the former having more de-centering of the gaze while in the latter there are more fixations on the text, but little efficient.

Eye tracking has also been used to observe and analyze the visual behavior of people suffering from neurodegenerative diseases, as are the Alzheimer's or Parkinson's, and mental disorders such as schizophrenia, autism spectrum disorders, depression or brain injuries.

Its usefulness in eating disorders is of special mention. Through these devices, combined or not with virtual reality, it is possible to know where people diagnosed with anorexia nervosa are looking the most. It is expected that they focus their gaze especially on those places where they feel the most complex.

Bibliographic references:

• Adler FH & Fliegelman (1934). Influence of fixation on the visual acuity. Arch. Ophthalmology 12, 475.
• Buswell, G.T. (1922). Fundamental reading habits: A study of their development. Chicago, IL: University of Chicago Press.
• Carpenter, Roger H.S. (1988); Movements of the Eyes (2nd ed.). Pion Ltd, London. ISBN 0-85086-109-8.
• Huey, E.B. (1968). The psychology and pedagogy of reading. Cambridge, MA: MIT Press.
• Yarbus, A. L. (1967). Eye Movements and Vision. Plenum. New York.
• Porras Garcia, Bruno & Ferrer-García, Marta & Ghiţă, Alexandra & Moreno, Manuel & López-Jiménez, Laura & Vallvé-Romeu, Alba & Serrano, Eduardo & Gutiérrez-Maldonado, José. (2019). The influence of gender and body dissatisfaction on body ‐ related attentional bias: An eye ‐ tracking and virtual reality study. International Journal of Eating Disorders. 52. 10.1002 / eat.23136.