Eye tracking primarily measures where people are looking – their so-called visual attention. There are several basic metrics that are used in eye tracking, but as an advanced eye tracking researcher you can derive more information from eye tracking tools than just visual attention. Emotional indicators like arousal and cognitive workload can be calculated from advanced eye tracking metrics, giving you a finer picture of how people react when they see something. Those advanced metrics are described below.
1. Pupil size / dilation
Almost every eye tracker provides data about the size of the pupil automatically as the exact location of the pupil is required in order to make accurate measurements. Pupil size can be measured over time and adds value to certain areas of research. An increase in pupil size is referred to as pupil dilation, while a decrease in size is a pupil constriction. The pupil usually responds to three different things: changes in light, changes in cognitive load and changes in arousal. Pupil dilation is correlated with emotional responses – especially emotional arousal. It can, however, also be used to quantify cognitive workload. Furthermore, cognitively demanding tasks are generally associated with widening of the pupil and longer periods without blinks. However, pupillary responses alone don’t give any indication of whether arousal arises from a positive or negative stimulus.
2. Distance to the screen
Eye trackers also measure screen distance and relative position of the respondent. Leaning forwards or backwards in front of a remote eye tracker is tracked directly and reflects for example valence. In aroma research, leaning forward towards the odor would mean a positive response (attraction) while leaning backwards would be interpreted as a negative response (approach and avoidance). Screen distance can also be interpreted as an engagement measure. However, interpreting the data is always very specific to the application. In computer games or usability, distance could be used to infer engagement. Of course, researchers can also utilize distance as marker in their datastream to determine when participants are shifting in their chair.
3. Ocular vergence
Most eye trackers measure eye positions of left and the right eyes independently. This allows the extraction of vergence, i.e., whether the fixations of left and right eyes move together or apart from each other. While just looking at a screen our eyes converge, but when we look beyond the screen towards the horizon our eyes diverge. This phenomenon is just a natural consequence of focusing near and far. Divergence often happens when your mind drifts away, when losing focus or concentration. It can be picked up instantly by measuring inter-pupil distance. One possible application for this could be: when an audience is presented 3D films, the 3D effects often trick the eye to focus out of the screen plane (behind or front), which can cause nausea. In order to find the most problematic scenes in a 3D film it can be examined using the vergence metric to pinpoint the moments when eyes get tricked. The film can then be edited to minimize nausea.
Eye tracking can also provide essential information on cognitive load by monitoring blinks. Cognitively very demanding tasks can be associated with delays in blinks, the so-called cognitive blink. It is often observable when attention shifts from one item to another. However, many other assertions can be derived from blinks. A very low frequency of blinks for instance is usually associated with higher levels of concentration while a very high frequency argues for drowsiness and lower levels of focus and concentration.
Blinking behavior could be used to find the ideal moments to cut films in production. Walter Murch on his work on Apocalypse Now:
“Coherent blinking would be a strong indication that the audience was thinking together, and that the film was working. But when the blinking became scattered, it would indicate that he may have lost his audience…”
(In a blink of an eye, Chapter A Galaxy of Winking Dots, p70)
Please contact the team at iMotions if you would like to get started with eye tracking, or if you would like to integrate further biometric research tools to improve data collection and analysis standards. Request a demo of our enabling software platform here.