The eyes are said to be the window of the soul, but they also allow us to know the way 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 attracts our attention of an ad.
Eye Tracking, or eye 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 from the world and, for this reason, eye tracking techniques have become increasingly important in research. Let's take a closer look at these techniques.
What is Eye Tracking?
The Eye Tracking, also known as eye tracking, refers to the set of techniques that allow you to assess where a person is looking, what object or detail in particular is focused and how long they keep their 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 itself.
Eye tracking techniques have been used in research in different fields, such as cognitive linguistics, psychology, and also marketing and product design. They are techniques that allow to know the visual behavior of a person, be it subject, patient or buyer, and based on this, draw conclusions about what their interests are, their emotional state or even if they have any type of pathology.
History
Although nowadays eye tracking techniques use modern devices that record the movement of the eyes or the direction of the gaze, the truth is that the first attempts to know where people looked when doing a certain type of task date back to the 19th century. These first attempts were made by direct observation of where the subject was looking, and what kind of striking information or 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, for example, when reading a book, you followed each line 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 saccadic movements.
During the 20th century, attempts were made to resolve various questions related to reading, such as what were the words they stopped the most, how much time was spent on them, and how and why they went back and reread words already read. Edmund Huey, with the intention of solving these questions, designed a contact lens with a hole that was placed directly in the participant's eyes. With these lenses he could record, very precisely, the movement of the eyes when he was reading, and what he was looking at.
Since Huey's technique was, despite being objective and effective, quite annoying and invasive, other researchers invented their own "eye trackers", which limited themselves to accurately recording eye movement without having 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 from the eye and that, when the eyeball moved, the light ray was deflected, recording the process on film .
During the 1950s and 1960s it was discovered that eye movement, both in front of a text and an image, could be conditioned by the task that the participant had to carry out, or his interests. This was the case of the investigations of Alfred L. Yarbus, who concluded that eye movement did not depend solely on what was in front of the subject, but also what he expected to find influenced.
Currently, eye tracking devices have been improved and have become much more accurate and less invasive. They have 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 look at the most. Since the 2000s, eye-tracking devices for people with motor disabilities have been manufactured, which interpret eye movements as commands, for example, causing the wheelchair to move or utter a phrase looking at the words in a screen.
Types of eye trackers
Although most eye trackers today 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
Something attached to the eye is used, such as a contact lens with a built-in mirror. This type of eye tracking is quite invasive, as its name indicates, since it involves placing something in the subject's eye that moves according to how the eyeball does it.
Since the eyes are delicate organs and, as a general rule, people are very sensitive to being touched, there are not a few times in which the participant refuses to have an invasive sensing eye tracker placed. 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 with enough precision, since they move according to how it does it. The recordings obtained using 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 often 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, looking at the position of the blood vessels of the retina.
In general, optical methods have good consideration in the field of research, since they are low in cost and are not invasive.
However, they may fail to record eye movement, as they sometimes do not accurately detect the pupil, cornea, or any eye track they use to do eye tracking. Furthermore, if the subject closes his eyes, his visual behavior cannot be recorded.
Some virtual reality devices, such as FOVE glasses, have eye trackers of this type, allowing to know what places the person is looking at once immersed in the virtual environment.
3. Electric potentials
A rather special eye tracking technique is one that uses electrical potentials, measured with electrodes placed around the eyes.
The eyes are the source of an electric potential field, which can be measured even with the eyes closed. The electrodes can be placed in such a way that a dipole is generated, 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 it 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 entirely invasive, it involves having to place electrodes, something that implies having to scratch the subject's skin a little. Furthermore, the care of these electrodes is quite delicate, and they can fail very easily or not conduct the current well depending on the subject's skin.
Eye Tracking Applications
Eye tracking has been shown to be 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 buyers, to know what details in an advertisement, both on television, in the newspapers or on the web, are more fixed.
Thanks to this, companies can make quantitative studies of how communication, that is, their ads, are perceived by the population, and how to improve it. It is also possible to know the impact of audiovisual advertising, both in a neutral, that is, experimental, context and in life itself.
By knowing what details users look at the most, it is possible to improve companies' web pages to make them more attractive and manageable for potential buyers, in addition to keeping their attention and directing them towards the purchase of the product or service.
But not only eye tracking focuses on how to advertise products, but also how they should be packaged. With eye tracking you can see which stimuli of a certain color, shape or various visual characteristics the subject pays the most attention to. In this way, companies can design their products and their packaging to induce their purchase.
People with disabilities
Eye monitoring has the great advantage of being able to help people with reduced mobility, such as people with tetraplegia or cerebral palsy.
Eye tracking by non-invasive sensing can be combined with computer screens, on which letters that the user can see appear. By fixing your gaze on those letters, a device forms words and phrases that sound through a speaker, allowing people with speaking problems to communicate.
You can also do the same to get the wheelchair moving. The person fixes his gaze on the screen, where arrows appear indicating the direction. Fixing his gaze on each of these arrows, he sends the order to the mechanized wheelchair to move in the desired direction.
Psychology
By studying visual behavior, it is possible to know if a person manifests some type of pathology, or how his way of looking at things differs from that expected in a person without a psychopathological diagnosis.
It has been observed that people with attention deficit hyperactivity disorder decentralize their eyes much more easily than people without diagnosis.
This causes them to not pay due attention to elements such as the class board or the textbook, promoting learning and comprehension problems that can be confused, in the most serious cases, with dyslexia or even mental retardation.
It should be said that eye tracking techniques can be very useful in diagnosing both ADHD and dyslexia because, although both have reading problems, the pattern of visual behavior differs, with the former being more misalignment of the gaze while in the second, there are more fixations in the text, but not very efficient.
Eye tracking has also been used to observe and analyze the visual behavior of people who suffer from neurodegenerative diseases, such as Alzheimer's or Parkinson's, and mental disorders such as schizophrenia, autism spectrum disorders, depression or brain injuries.
Of special mention is its usefulness in eating disorders. Through these devices, combined or not with virtual reality, it is possible to know where people diagnosed with anorexia nervosa look most. It is expected that they focus their eyes especially on those places where they feel more complex.
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