Eye Tracking in User Experience Design

Jennifer Romano Bergstrom, Andrew Schall, Jennifer Romano Bergstrom, Andrew Schall

• Publisher: Morgan Kaufmann
• Year: 2014
• ISBN:
  9780124167094
• Topic: Ciencia de la computación
• Subtopic: Interacción persona-computadora

Eye Tracking for User Experience Design explores the many applications of eye tracking to better understand how users view and interact with technology. Ten leading experts in eye tracking discuss how they have taken advantage of this new technology to understand, design, and evaluate user experience. Real-world stories are included from these experts who have used eye tracking during the design and development of products ranging from information websites to immersive games. They also explore recent advances in the technology which tracks how users interact with mobile devices, large-screen displays and video game consoles. Methods for combining eye tracking with other research techniques for a more holistic understanding of the user experience are discussed. This is an invaluable resource to those who want to learn how eye tracking can be used to better understand and design for their users.

• Includes highly relevant examples and information for those who perform user research and design interactive experiences
• Written by numerous experts in user experience and eye tracking
• Highly relevant to anyone interested in eye tracking & UX design
• Features contemporary eye tracking research emphasizing the latest uses of eye tracking technology in the user experience industry

Section 1

Overview of Eye Tracking and Visual Search

Outline

1 Introduction to Eye Tracking

2 Visual Search

1

Introduction to Eye Tracking

Andrew Schall¹ and Jennifer Romano Bergstrom², ¹Spark Experience, Bethesda, MD, USA, ²Fors Marsh Group, Arlington, VA, USA

Abstract

This chapter contains a brief history of eye tracking and how it has become a valuable methodology for user experience researchers. Readers will gain a basic understanding of how eye trackers can track the location of a user’s eye gaze and common visualizations used to analyze the eye-tracking data output.

Keywords

eye tracker; eye tracking; history of eye tracking; user experience; user research; UX; vision science

What is eye tracking?

Eye tracking is a methodology that helps researchers understand visual attention. With eye tracking, we can detect where users look at a point in time, how long they look at something, and the path their eyes follow (Figure 1.1). Eye tracking has been applied to numerous fields including human factors, cognitive psychology, marketing, and the broad field of human–computer interaction. In user experience research, eye tracking helps researchers understand the complete user experience, even that which users cannot describe.

Figure 1.1 Participant using a computer equipped with an eye tracker. (Courtesy of Tobii Technology.)

How eye tracking works

An eye tracker is a tool that allows user experience (UX) researchers to observe the position of the eye to understand where an individual is looking. Most modern eye trackers rely on a method called corneal reflection to detect and track the location of the eye as it moves. Corneal reflection uses a light source to illuminate the eye, which then causes a reflection that is detected by a high-resolution camera. The image captured by the camera is then used to identify the reflection of the light source on the cornea and in the pupil, as shown in Figure 1.2. Advanced image processing algorithms are then used to establish the point of gaze related to the eye and the stimuli.

Figure 1.2 A conceptual illustration of how eye-tracking technology works.

The same eye-tracking methodology applies no matter what the individual is looking at. Even though our vision appears extremely stable, the eye is constantly moving around to help construct a complete picture of what we are looking at.

This process is divided into fixation and saccades. A fixation is the pause of the eye movement on a specific area of the visual field. These pauses are often extremely brief, as the eye continually performs saccades. Saccades are rapid movements of the eye from one fixation to another to help the eye piece together a complete scene of what an individual looks at. You might assume that fixations and saccades give us a clear picture of what an individual perceives, but this is not the whole story.

Fixations take place in our foveal vision, which accounts for nearly half of the visual information sent to our brain (see Figure 1.3). This part of our vision is highly detailed and provides complete clarity about what we are looking at. Our primary attention is usually focused on what we register in our foveal vision. Eye trackers only track what is registered in an individual’s foveal vision. Unfortunately, this only accounts for less than 8% of our visual field (Tobii Technology, 2010).

Figure 1.3 Representation of the human visual field. (Courtesy of Tobii Inc.)

The rest of our vision is composed of parafoveal and peripheral vision. These regions surround our foveal vision and help us to gain a sense of what is happening around us. These types of vision are almost certainly the result of evolution where our ancestors needed to worry about potential predators out of the corner of their eye. Stimuli registered in either parafoveal or peripheral vision tend to be things that involve a lot of movement (again, think about human evolution). The stimuli detected are low resolution and only give us a sense of an object’s general color, shape, and motion (Rayner, 1998).

While we cannot detect the details of objects in these regions of our vision, our brain is pretty good about theorizing what the object could be. This is an extremely powerful capability that provides us with the ability to scan a website and get the lay of the land within a few moments without carefully reading all of the content. Our mind can compose a high-level understanding of a scene within seconds.

This makes it tricky to analyze eye-tracking data. Just because a user did not specifically fixate an image does not mean that they are not aware that it is there. They might even be able to identify page elements without fixating them for any detectable period of time.

Eye tracking’s unique ability to detect and follow the eye as it looks at stimuli has given UX researchers and designers a much better understanding of how the human visual system works.

What eye trackers can and cannot tell us

An eye tracker can be a powerful tool that gives us a highly accurate representation and understanding of an individual’s eye movement behavior. The three attributes of location, duration, and movement form the basis for this understanding.

Location

The location of a user’s eye gaze at a particular moment in time (i.e., a fixation) provides the most basic unit of analysis for understanding visual attention. Fixations are extremely short and typically only last between 100 and 600 milliseconds. Fixations can be mapped to specific x and y coordinates on a grid that help pinpoint where the user looked on a given display (Figure 1.4).

Figure 1.4 Fixations are mapped to x and y coordinates on a grid.

The challenges with interpreting mapped fixations lie in the fact that just because a fixation was registered does not necessarily mean that the user really saw it or that it registered cognitively in their brain. This is often the case with orphan fixations where the eye may have momentarily rested in a random area of the screen but did not intentionally look at it, such as when users complete forms that require created answers, as discussed in Chapter 5. In these cases, users look at the screen, but their attention is elsewhere, and thus the eye-tracking data are not useful.

The clustering of a number of fixations in a particular region can provide more evidence that the user deliberately looked at something, and significantly increases the likelihood that the brain processed it. However, eye trackers are not mind-reading devices, and they can only tell us what the person looked at but not why.

Duration

The length of time that a user fixates a particular area on the screen (as shown in a gaze plot diagram in Figure 1.5) helps us to understand whether he/she is paying particular attention to a specific visual element. The duration of fixations is often extremely short and is typically represented in milliseconds.

Figure 1.5 Eye trackers can detect the length of a given fixation, and can represent longer and shorter durations by increasing and decreasing the relative size of the dots in a gaze plot visualization.

Unfortunately, duration is a particularly difficult measurement to interpret. There are many possible reasons why a user fixates for a relatively short or long period of time on a particular area. Are they confused by this element? Do they find it engaging? In order to understand these measurements we need to look at the data in context with other research methods. This will be discussed extensively in Chapter 3.

Movement

The movement of a user’s eyes is based on saccades from one fixation ...