Opinion: the use of eye-trackers to record eye movements helps researchers assess what people’s brains are processing

In 1980, Marcel Just and Patricia Carpenter formulated the influential eye-mind hypothesis that suggests a strong link between eye movements and brain processing. This implies that if we analyse someone’s eye movements on a computer screen,  we can figure out the area of that screen that his or her brain is dealing with, what is attractive or what part of a text is difficult to understand.

Understandably, the theory has critics, as it is impossible to affirm irrefutably that all eye movements indicate related brain processes. Take, for example, a person who is looking at the screen, but is really thinking about her holiday - a very good example on a chilly winter’s day! If we were to analyse her eye movements on the screen, we might establish that she is thinking about a text or looking intensely at an image when she is actually dreaming about a beach in Lanzarote!

Despite this caveat, researchers have studied eye movements to understand what people’s brains are processing long before using fMRI scans to explore brain activity. Even today, the most convenient, inexpensive and non-intrusive method of exploring the black box of our mind is to look at people’s eyes. While you might wonder why not ask a person directly what she is thinking, research has shown repeatedly that what we do and what we say we do are often two different things.

"The most convenient, inexpensive and non-intrusive method of exploring the black box of our mind is to look at people’s eyes"

But how can we look at people’s eyes? The eye-tracker is the "machine" that lets us see eye movements and pupil dilation to establish how busy the brain is when the eyes are looking at an area. In the 1800s, researchers developed the first eye-trackers. It was then a very intrusive and uncomfortable piece of equipment handmade by those same researchers.

Since the 1970s, however, specialised companies have built eye-trackers that are more accessible. This has resulted not only in the creation of less intrusive hardware, but also in the development of easy-to-use software that helps to read and visualize the quite complex and detailed eye-tracking data. The use of eye-tracking in research has exponentially grown since then.

Nowadays, eye-trackers can record people’s eye movements through mounted high-resolutions cameras and infrared lights that aim to track the pupil and the corneal reflection. By means of a software package, a researcher can analyse the data from the eyes: fixations (a pause and focus of the eye movement to a certain area of the visual field), visits to a defined area of interest, pupil dilations, gaze points, length etc

Dikablis Eye Tracking Glasses from Ergoneers

After analysing this data, the researcher can hypothesize about how a person reads a text or webpage, if a consumer prefers one brand over another in a supermarket or even analyze a visitor’s experience in a museum or a hotel. Because we are not necessarily always looking and paying attention to the same thing for the same reasons, experiments involve parallel data gathering. This includes surveys, retrospective "thinking aloud protocols" (when participants watch a video of their eye movements and explain their actions or thoughts), interviews, facial expression analysis, electrocardiography and galvanic skin response, among others.

The two visuals below show a user changing the font in a word processor. The eye-tracker used is a Tobii X60XL at 60 Hz. This means that the eye-tracker took 60 pictures of the eyes, i.e. measurements, every second. Figure A shows a cluster of fixations, while the heatmap in Figure B shows a group of fixations in a way that is visually attractive. The "hotter" the area (that is, the spots in red), the more the eyes fixated in that area of the screen - in this case, to select the type of font requested in the test.

Figure A: Gaze plot
Figure B: Heatmap

There are several types of eye-trackers that suit different studies. For example, if the researcher is looking to recreate a natural setting in sports research, she might decide to use a head-mounted eye-tracker or eye-tracking glasses. If, on the other hand, the researcher is looking to recreate an office setting, she might use desktop eye-trackers with a head support or remote eye-trackers (remote here means that the participant can move the head freely).

How is eye-tracking helping science and people? Eye-tracking is used in psychology, medical research, usability and human computer interaction studies and marketing campaigns. As a result, it has contributed extensively to learning about reading, use of websites, interaction with technology, transport usage, memory processes, second language acquisition, translation, shopping and problem solving. It has also helped to assess medical conditions such as attention deficit disorder, autism spectrum disorders, obsessive compulsive disorders, or Alzheimer’s disease. The next time you look into someone's eyes, appreciate the scientific potential this part of our body has as a unique window to our brain, as well as that person's beauty and the eye's capacity to show us the world around us.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ