September 14, 2010

What You Always Wanted to Know About Eye Tracking - Part 3: Terminology

In part 1 and part 2 of this series, some fundamental aspects of the eye tracking technology that affect data gathering have been covered. The next parts will cover more advanced conceptual-methodological topics, related to data analysis and data interpretation. Being aware of these issues is important because we are still far from having a unified framework for analysis and interpretation of eye tracking data.

Problems can already arise when it comes to terminology.

Problems caused by a lack of shared terminology
Working in a scientific context goes along with using a specific terminology, which includes a shared understanding of certain well-defined objects/phenomena and the terms that refer to those.

Especially in relatively new disciplines and concerning relatively new methods, a standard – and shared – terminology has not yet been established, which bears the danger of implicit misunderstandings when communication partners use the same terms, but have different concepts in mind. This is also true for the eye tracking domain, where the same words in different studies do not guarantee that researchers refer to the same concepts.

This was also observed by Jacob and Karn (2003) who assembled an overview of eye tracking studies in the context of usability engineering. They defined "gaze duration" as "cumulative duration and average spatial location of a series of consecutive fixations within an area of interest. .... A fixation occurring outside the area of interest marks the end of the gaze" (p. 581). They point out, however, that "some authors use 'gaze duration' differently, to refer to the total time fixating an area of interest during an entire experimental trial (i.e., the sum of all individual gaze durations)" (p. 599).

Besides the homonym-issue (same word for different things), there is also a synonym-problem (different words for the same thing). Jacob and Karn point out that other authors also refer to the described "gaze duration" concept, but use different words to do so: "Authors cited ... have used 'dwell', 'glance' or 'fixation cycle' in place of 'gaze duration'" (p. 581).

It is obvious that, when different eye tracking studies shall be compared, such terminology issues can cause problems when one is not aware of their existence. In the worst case, false interpretations of results are the consequence.
It is therefore recommendable to explain the terminology used when reporting eye tracking results. Until a terminology is established that is shared throughout the eye tracking community, this is the only way to avoid (implicit) communication problems.

Jacob, R.J.K. & Karn, K.S. (2003). Eye tracking in human-computer interaction and usability research: Ready to deliver the promises. In J. Hyönä, R. Radach & H. Deubel (Eds.), The mind’ s eye: Cognitive and applied aspects of eye movement research (p. 573–605). Amsterdam: Elsevier.

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