Ever wondered why you’re losing out on revenue? Can’t make head or tail of the fact that your website visitors just don’t seem to click that flashy button you want them to hit in order to take action? What exactly goes wrong?
Eye tracking data can deliver valuable insights into the gaze patterns of your website visitors – how long does it take them to find a specific product on your site, which kind of visual information do they ignore (but are supposed to respond to)? Where do your website visitors look? What do they look at and how much time do they spend looking at it?
To date, eye tracking is the only method in human behavior research rendering it possible to objectively measure and quantify eye movements in real time.
With the evolution of computer technology, eye tracking has become a non-intrusive, affordable, and easy-to-use tool in human behavior research that allows measuring visual attention as it objectively monitors where, when, and what people look at.
Given the ease of application and measurement, it is no wonder that eye tracking technology finds increasing popularity among a rapidly growing variety of academic and commercial disciplines (website testing is just one of many examples how eye tracking can be leveraged).
So what is eye tracking?
A technical (and not-so-technical) definition
Put most simply, eye tracking refers to the measurement of eye activity. More scientifically, eye tracking implies the recording of eye position (point of gaze) and movement on a 2D screen or in 3D environments based on the optical tracking of corneal reflections to assess visual attention.
In less technical terms, eye tracking reveals
- which visual elements attract immediate attention
- which visual elements attract above-average attention
- if some visual elements are being ignored or overlooked
- in which order the visual elements are noticed
- how the visual material compares to other material
Eye tracking technology
Optical tracking of corneal reflections? Exactly … and here’s how it works.
Most modern eye trackers available on the market utilize near-infrared technology along with a high-resolution camera to track the movement of the eyes. The underlying concept, commonly referred to as pupil center corneal reflection (PCCR), is rather straightforward:
Near-infrared light is directed towards the center of the eyes (pupil), causing visible reflections in the cornea (outer-most optical element of the eye). These reflections are tracked by a camera.
Does eye tracking work with an ordinary light source (say a bright table lamp)?
The answer is a clear no (sorry). Since the accuracy of gaze direction measurement relies on a clear demarcation of the pupil and the detection of corneal reflection, only infrared spectrum imaging will lead to satisfying tracking results.
Why? While the visible spectrum is likely to generate uncontrolled specular reflection, infrared light is not perceivable by the human eye and therefore allows for a precise differentiation between the pupil and the iris – while the light directly enters the pupil, it just „bounces off“ the iris.
Screen-based eye tracking and eye tracking glasses
Irrespective of the technology, there are two different types of eye tracking devices:
- screen-based eye trackers (which are also called desktop, stationary or remote)
- eye tracking glasses (which are also known under the term head-mounted)
Let’s have a look at the key features of each:
Screen-based eye trackers
Screen-based devices require respondents to sit in front of a monitor and interact with screen-based content. Although remote devices track the eyes only within certain limits (the so-called headbox), the freedom of movement is still sufficiently large for respondents to feel unrestricted.
Eye tracking glasses
As the name implies, mobile devices are fitted near the eyes (usually mounted onto eyeglass frames) and allow respondents to move freely. Clearly, this is a plus if your study design requires performing tasks in a natural environment. On the downside, the glasses might shift during the recording if mounted sloppily.
Screen-based or glasses – at this point, you might tend to conclude that all eye tracking systems are pretty much the same. Their only job is to track where people are looking and what they are looking at, so what’s the difference anyway?
Don’t judge too fast. Actually, there is a difference. Eye tracking is on the rise, and to keep pace with demand, new systems are continuously being pushed onto the market. Amidst all manufacturer specifications, it can be quite hard to keep the overview and evaluate which eye tracker is right for your research endeavor.
Which recording device should you go for? Start with the obvious:
- Will your respondents be seated in front of a computer during the session? Go for a screen-based eye tracker.
- Do your respondents need to move freely in a natural setting or virtual reality? Choose a head-mounted system that allows for head and body mobility.
Good. Now that you have clarified which kind of tracking system suits your study design, it’s time to read the fine-print. Before your purchase, think about these key questions that can make or break your research:
- Eye tracking camera: Which camera is integrated into the eye tracker? Don’t be blinded by eye trackers that integrate ordinary low-resolution webcams and use no infrared light.
Even though they appear to be a good bargain and the ideal solution for smaller budget (“that will do for starters”), the lack of a controlled light source along with a rather weak camera performance will diminish the quality of your data significantly.
Our advice: When it comes to eye trackers it‘s absolutely worth spending a bit extra money if you‘re aiming for high-quality results (which you should).
- Integrated vs. standalone eye trackers: Is the eye tracking hardware integrated into the monitor frame? Standalone eye trackers are more flexible, but typically a bit more complex to set up.
- Sampling rate: How many times per second does the eye tracker measure the eye position? While the typical value ranges anywhere between 30 and 60 Hz, special research equipment usually samples at 120-1000+ Hz.
- Recapture rate: How fast does the eye tracker detect the eye position after the eyes have been out of sight for a moment (e.g. during a blink)?
- Measurement precision: How precise does the eye tracker measure gaze direction (measured in degree)? While less expensive hardware starts around 1.0 degree, high-end trackers measure down to 0.1 degree (or lower).
Speaking of measurement accuracy.
A common misconception is that researchers face an inevitable tradeoff between measurement accuracy and freedom of head motion.
Let’s clear this up: Certainly, measurement precision is key in eye movement research. Primarily, the quality of the collected data depends on the tracking accuracy of the device you use – going for a low-quality system may be detrimental when you shoot for high precision data.
So do remote eye trackers really offer a higher level of precision compared to their mobile counterparts?
To put it plain and simple: They don’t. If calibrated properly, head-mounted eye trackers effectively compensate for any head movements that could impair the signal (and therefore measurement precision). In fact, they are able to deliver high precision gaze data just like remote devices. Also, since the eye tracking camera is locked directly to the head‘s coordinate system, the transformation of eye movements onto the scene camera won’t implicate errors due to (unwanted) head movement.
Eye tracking metrics
Like no other experimental method, eye tracking renders it possible to quantify visual attention as it objectively monitors where, when, and what people look at. So much for the hard facts.
Time to get practical and throw a glance into the most common metrics used in eye tracking research.
- Gaze points and fixations: Definitely the most prominent metrics in eye tracking literature. Gaze points constitute the basic unit of measure – one gaze point equals one raw sample captured by the eye tracker. Gaze points can be aggregated into fixations, a period in which our eyes are locked toward a specific object.
- Areas of interest (AOI) and heat maps: To concentrate the analysis on specific regions on the stimulus, areas of interest (AOI) can be defined. Heat maps visualize fixation positions and temporal changes of fixations as an overlay on a specific stimulus across different respondents.
- Fixation sequences and further metrics: There are several ways to analyze gaze positions and fixations, for example you can analyze the fixation sequences and the performance of different regions in an image or a video with respect to the time of first fixation (TTFF) or the number of respondents looking toward a specified region (respondent count).
While these eye tracking metrics are commonly used to track visual attention, there are a few others that allow to assess states of emotional arousal and cognitive workload. Those “advanced” metrics include pupil size dilation, distance to the screen, ocular vergence, and blinks.
If you have any questions on how iMotions can help with your eye tracking research please feel free to contact us.