Learn how to use RealEye.io - distributed webcam eye-tracking platform.

Beata Lewandowska
Written by Beata Lewandowska

What is AOI?

And what metrics it provides for fixations and for gaze points?

Area Of Interest (AOI) is an analytical, easy to use tool that allows calculating quantitative eye movement measures. You simply draw a boundary around an area of a chosen image that interests you and you received desired metrics:

  • for fixations (read more about fixation filters):
  • average TTFF (Time To First Fixation) - the amount of time that it takes participants (on average) to look at this area for the first time,
  • average time spent - the amount of time that participants spent on average looking at this area,
  • fixations - number of fixations within this area (more fixation means more visual attention),
  • ratio - how many of all the viewers (for whom eye-tracking data is collected for the item) left at least one fixation within this area,
  • average fixation duration - the time that the average fixation lasted for,
  • average FFD (first fixation duration) - how long on average lasted the first fixation;
  • for gazes:
  • average TTFG (time to first gaze) - how long it took the testers on average to first look at this area in seconds (when the first gaze sample was taken),
  • average time spent - total time spent by viewers (on average) at this area,
  • gazes - how many gazes were registered within this area,
  • ratio - how many of all the viewers saw this area (based on gazes);
  • for both:
  • average revisits - how many times (on average) participants looked back at this area (looked at it, looked away and then looked back again); AOI visit is detected if there's a fixation within the AOI (or many fixations "one after another"),
  • clicks - how many clicks there were on the given area (in total),
  • TTFC (Time To First Click) - the amount of time that it takes participants (on average) to click at this area for the first time,
  • AOI size - expressed as the percentage value relative to the size of the entire image; it's recommended to make AOIs of at least 5-10% of the item size,
  • AOI time range - the time for which the values of the AOI were calculated (you can set this time with the orange slider under the heatmap),
  • word count - how many words were registered within the area.


We consider gaze/fixation to be a part of an AOI if the fixation started in the AOI time range.


All of the AOI data is displayed for the time set with an orange slider (the first 0.5s is "cut off" by default to avoid the bias in the middle of the item). We call this "AOI time range". So if you want to analyze only the data between the first and the third second of your image display, set the beginning of the orange slider to 1 second and the end to 3 second - the heatmap and AOI data will be recalculated.


For a single participant, those "average" statistics are based, of course, on data only from this participant, so, i.e., "average TTFF" is a time that it took this particular participant to look at this area for the first time.

There are two important variables in making AOI - placement and size. You want to put an AOI over an item that you are interested in. The example shown below is a project of Coca-Cola ad. A researcher working on it would like to know what values have mentioned previously parameters for main features of the image - Coca-Cola logo, bottles with Coca-Cola and a woman’s face to find out if they are well seen and which one draws the most attention. The second variable is the size. It’s a balance between selectivity and sensitivity. Smaller AOI means higher selectivity but lost on a sensitivity, because it cuts out some of the extraneous gazes, so it could mean a loss of some valid data. That means you have to think ahead about how to obtain the best data possible.