Viewing People Viewing Documents: Eye-Tracking and Usability

 
I just finished reading a very informative article, written by Lauren Cooke, about eye-tracking technologies and how they can be incorporated in usability studies.  It also details the patterns in which our eyes move when we read, whether the document in question is online or in print.

Eye-tracking data can be obtained through head-mounted or remote cameras.  In either case, the movement of the iris is recorded and subsequently analyzed using software that reveals the fixations (which "occur when the eye is focused on a particular point on a screen") and saccades (which happen when we "move the eye from one fixation to the next fixation") made by viewer.  The combination of fixations and saccades produce scanpaths that provide a more comprehensive picture of how that particular viewer went about visually analyzing the given document.  An example of what a typical scanpath of a printed text appears below.

(public-domain image, found here)

As Cooke explains, "Eye tracking as a methodology is based on Just and Carpenter's (1976) 'eye-mind' hypothesis: the location of a person's gaze directly corresponds to the most immediate thought in a person's mind."  Therefore, the data from eye-tracking studies can be applied in a variety of fields.  For example, such data has been obtained from pilots while they were flying planes, helping engineers to redesign cockpits to ensure maximum usability.  Studies are also being conducted to determine how people view PDA displays and other compact screens relative to how they go about visually analyzing material on standard computer screens.  Furthermore, eye-tracking data obtained from people reading printed documents reveal that font sizes smaller than 9 pts. and larger than 12 pts. tax the reader by degrading letter legibility and preventing words from being read as a whole entities, respectively.  People also tend to read at slower speeds, and temper their tendency to skip over words consisting of three letters or less, when reading complex material.

In addition to the information detailed above, eye-tracking data can, when combined with think-aloud studies, provide a great deal of insight into the problems people may experience when performing a particular task or looking at a given document.  People, in general, aren't very proficient at identifying and articulating their visual impressions, since people process visual data much quicker than they are able to consciously recognize and verbalize what they see.  Thus, eye-tracking and think-aloud data can be used to determine what areas of a document or interface are preventing them from accomplishing their goals.  Additionally, eye-tracking data can be used to determine people's general tendencies in their efforts to visually process the information that is in front of them.  For example, long paragraphs have been found to be less engaging than short ones, and people generally look at the top and bottom of a menu/list before looking at the middle portion.

If used properly, studies using eye-tracking technologies can provide valuable information for web and usability designers.  Data shows that people "do not necessarily follow the same scanpath for every type of Web site; instead, there appear to be universal scanpaths that people develop based on the function, genre, and design of a Web site."  Further research in this area may help designers to configure their sites to accommodate these various scanpaths.  Some of the findings detailed previously in the post can also be applied to web design, as can these conclusions drawn by researchers:

--People tend to read small type closely, but they're more likely to scan when reading text written in larger type.

--Readers often will not read the material that appears below an underlined headline.

--Eye movements are generally made in the shape of the letter "Z" when first looking at a website (i.e., starting at the top left-hand corner, then going to the top-right hand corner, etc.).  Readers are likely to make smaller "Z" patterns as they more closely examine the page after the initial scan.

--While objects that appear in isolation do draw attention, that attention is not sustained for as long as some designers may think.  Therefore, the isolated element that artists and designers want viewers to focus on should also be given another distinctive feature, like being drawn in a different color.

--People are more likely to read a story when they are given both its headline and summary than they are when presented with only its headline.

--Images 210 x 230 pixels or larger draw more attention than smaller images, and people are likely to click on images of the size 210 x 230 pixels.  This fact should be taken into consideration by web designers when creating icons and navigational links.

--If web designers want to provide related information (like a footnote or other explanatory note), they should place it near the text or image it is related to, instead of at the bottom of the screen.  The farther away viewers have to move their eyes in order to read the note, the less likely they are to read it. 

Does any of the data here (or presented in the article, if you've read it) surprise you?  Do you have any personal experience with eye-tracking and its applications?  Do share.