Eye Tracking the User Experience. Aga Bojko

time-consuming. The recorded scene keeps changing due to head movement. As a result, the same gaze location in the recorded frames can indicate something different in the world: Because of this dissociation, data analysis is typically more manual and time-consuming. This problem can be at least partially solved by placing infrared markers in the environment, using edge/object detection, or adding a head tracker.

       Two Types of Remote Eye Trackers

      If you look closely at Figure 3.2, you’ll see that one of the eye trackers is different from the other two. The eye tracker on the top left is built into a computer monitor. The other systems are stand-alone. They could be used with a monitor (as shown in the top-right picture), but they allow for a more flexible setup.

      Stand-alone remote eye trackers can be used for tracking physical objects (such as magazines, newspapers, products, or even entire shelves), as long as these objects and the participant are stationary. They can also record eye movements on TV screens as participants play games, interact with on-screen menus, watch commercials, and look at large screen projections (for example, a virtual shelf). Some can be installed in vehicles to track how drivers use the dashboard and what they pay attention to on the road. In addition, it is possible to use stand-alone eye trackers for recording user interaction with mobile devices (see Figure 3.3).

FIGURE 3.3 These remote eye trackers together with their special stands can be used for studies with mobile devices.

      While it may sound like a good idea to get a stand-alone eye tracker because of its flexibility, the trade-off is that it tends to be a little more demanding to set up than a plug-and-play integrated eye tracker. So if you only conduct studies with stimuli displayed on a computer monitor (such as websites or software applications), an integrated eye tracker is definitely something to consider. An added bonus is the fact that it is even less obtrusive than a stand-alone eye tracker, which helps participants feel more at ease.

      If you’d rather not be limited to conducting studies on one computer monitor, fear not. Manufacturers have already managed to simplify the more challenging setup of stand-alone eye trackers. Some systems now also offer the capability to save the configuration details so that the configuration can be reused in similar studies. In fact, as these devices become smaller, lighter, and more portable, more and more practitioners opt for stand-alone remote eye trackers.

       So, Wearable or Remote?

      The general rule of thumb is to go with a remote eye tracker unless you are certain that your study calls for a wearable eye tracker. Reason? Because of the better scientific control (should you need it) and more efficient data analysis. So, while you could use a wearable eye tracker to test a website or images on a screen, a remote eye tracker would make your life easier, primarily due to the more automated analysis.

      On the other hand, if your objective is to validate the usability of the content and placement of signage at an airport or a train station, a wearable eye tracker will be your best option (see Figure 3.4). There is just no good way to conduct this type of study with a remote eye tracker, simply because participants will be moving around.

      Another good example of a clear-cut situation when you should use a wearable eye tracker is out-of-the-box research that aims to capture initial user experience with a product. An out-of-the-box study may require the participant to examine the product packaging, open the box, take out the product, and attempt to set it up while referring to the instructions (see Figure 3.5). A remote eye tracker wouldn’t be suitable in this case because participants would be picking things up and moving them around. Objects could obstruct the path between the eye tracker and participants’ eyes, and the task would likely require more head movement than allowed by remote eye trackers.

      

FIGURE 3.4 A wearable eye tracker is a must-have for eye tracking studies that require participants to move around real-world environments.

FIGURE 3.5 An out-of-the-box study with a wearable eye tracker.

      In many situations, however, choosing the most suitable type of eye tracker is less straightforward. Let’s say the goal of the study is to determine how a product package compares to other packages on the shelf in terms of the amount of attention it attracts. You could use a wearable eye tracker and conduct the study in a real store or in front of a shelf set up in a lab. But you could also use a remote eye tracker and project a virtual shelf onto a wall or even display a picture of the shelf on a computer screen.

      When both eye tracker types seem suitable, the decision comes down to the trade-off between ecological validity on one side and scientific control and ease of data analysis on the other side (see Table 3.2). Ecological validity is related to how closely the test environment and tasks resemble the real-life situation under investigation. Increasing ecological validity makes the study findings more generalizable to the “real world.” Scientific control, on the other hand, is the degree to which researchers can influence the study environment to minimize the impact of unwanted variables on the findings.

      In the packaging example, conducting the study in a store and using a wearable eye tracker would provide high ecological validity because of the realistic setting. The downside is that you might not be able to easily control how the package of interest to the study is displayed on the shelf. The findings may be skewed if participants always see the package of interest to the study next to a very attractive (or unattractive) package that just happened to be there. In addition, data analysis is likely to be more challenging than if a remote eye tracker and a virtual shelf were used.

      Conversely, showing participants a virtual shelf and using a remote eye tracker would decrease the realism of the situation, but it would allow you to systematically manipulate the location and order of the packages, thus eliminating the influence of confounding variables, which is a major advantage. This setup would also enable more automated analysis, thus saving time and decreasing the cost of the study.

      The discussion about packaging also applies to print. Testing paper bills, magazines, or instructions can be done with remote or wearable systems. While capturing the natural interaction using a wearable eye tracker is appealing, it is not always necessary. The objectives of the study may justify showing the stimulus in a more static way, thus allowing you to benefit from using a remote eye tracker. For example, if the study goal were to select the most effective water usage history presentation on a utility bill, displaying the designs on a computer screen would likely be sufficient.

TABLE 3.2 SHELF STUDIES OF DIFFERENT LEVELS OF ECOLOGICAL VALIDITY AND SCIENTIFIC CONTROL

      In addition to understanding the trade-offs associated with choosing the eye tracker type in general, it is important to keep in mind that eye trackers of the same type can differ quite a bit in their capabilities