What does eye tracking data tell us?

First,  sometimes  fixations  do  not  necessarily  translate into a conscious cognitive process. For example, during a search task one can easily fixate briefly on the search object and miss its presence, especially if the object has an unexpected shape or size  (commonly  called  change  blindness).  This  happens because our expectation of what the object  (or  scene)  should  look  like  modulates  our  visual attention and interferes with the object detection.  This  effect  can  be  eliminated  from  a  test if you give clear instructions to the participant, and/or  follow  up  the  eye  tracking  test  with  an  interview to assess the participant’s motivations or expectations.

Second,  fixations  can  be  interpreted  in  different  ways depending on the context and objective of the study. For example, if you instruct a participant to  freely  browse  a  website  (encoding  task),  a  higher number of fixations on an area of the webpage  may  indicate  that  the  participant  is  interested in that area (e.g. a photograph or a headline)  or  that  the  target  area  is  complex  and  hard to encode. However, if you give the participant a specific search task (e.g. buy a book on  Amazon),  a  higher  number  of  fixations  are  often indicative of confusion and uncertainty in recognizing  the  elements  necessary  to  complete  the task. Again, a clear understanding of the objective of the study and careful planning of the tests  are  important  for  the  interpretation  of  the  eye tracking results.

And third, during the processing of a visual scene, individuals  will  move  their  eyes to relevant features in that scene. Some of these features are primarily  detected  by  the peripheral  area  of  our  visual  field.  Due  to  the  low  acuity,  a  feature located  in this  area  will  lack  shape  or color  detail  but  we  are  still  able  to  use  it  to  recognize  well‐known structures and forms as well as make quick, general  shape  comparisons.  As  a  result,  we  are  able to use the peripheral vision to filter features according to their relevance to us, for example, if we  generally  avoid  advertisement  banners  on  webpages, we might also avoid moving our eyes to other sections of the webpage that have a similar shape  simply  due  to  the  fact  that  our  peripheral  vision  “tells”  us  that  they  might  be  banners.  The current eye tracker technology will only show the areas on the visual scene that the test subject has been fixating at and the jumps between them (i.e. not  the  whole  visual  field).  Thus,  to  fully  understand why a test person has been fixating on some  areas  and  ignoring  others,  it  is  important  that  the  tests  should  be  accompanied  by  some form of interview or think‐aloud protocols.