Working with dynamic stimuli in the AOI tool

Tobii Pro Studio

Learn more about and get some tips on how to work with AOIs on moving stimuli like movies or animations in Tobii Pro Studio.

If you’re studying visual behavior on moving stimuli like movies or animations, the Dynamic Areas of Interest tool provides the same analytical capability as the static AOI tool does for images and other still visuals. Drawing and modifying dynamic AOIs proceeds just like with static AOIs.

There are several important points to keep in mind about the Dynamic AOI tool.

  1. It is useful for aggregating gaze data for multiple users who see the same linear dynamic stimulus
  2. Dynamic AOIs can’t be used for nonlinear dynamic recordings
  3. Dynamic AOIs can’t be used for static stimuli like images
  4. Dynamic AOIs can be turned on and off, moved, and resized to track the targets of interest

First, let’s define the two different kinds of dynamic stimuli. Linear dynamic stimuli (LDS) are things like movies or animations that are of a fixed length and are viewed in the same order and with the same timing by all participants. For example, a 30-second-long movie clip would be linear dynamic. In contrast, nonlinear dynamic stimuli are characterized by individual paths and progressions and can be a different duration for each and every participant. A Tobii Glasses or Pro Glasses 2 recording or web-based tasks are the most common examples of this type of dynamic stimuli. While behavior on nonlinear stimuli can be isolated and visualized via the segment groups tool, at present there is no way to apply automated AOI analysis.

An additional consideration that can affect your choice of tools is the whether the target of interest on the LDS is actually moving in the frame. For example, if a movie stimulus has two stationary looking targets, like stuffed animals on either ends of a table top, one could analyze the gaze path with the scene tool using a frame from the recording as the backdrop for constructing static AOIs or displaying eye tracking visualizations (e.g., gaze plots or heat maps). If, however, the looking target is a person who enters the frame from the left edge of the screen and walks toward the right until he is out of frame, then the Dynamic AOI Tool would be appropriate.

Try out the Dynamic AOI tool

Tobii Studio screenshot


Let's get started! Much of the detail about the use of the tool can be found in chapter 8 of the Pro Studio User Manual, Creating and Managing AOIs. Using the Wildlife.wmv 30-second movie that comes with Windows systems, we're going to identify the key steps in applying the Dynamic AOI Tool after you've recorded your participants.

  1. Go to the Areas of Interest tab in Pro Studio and select the stimulus under the “Movies” media category
  2. Using the playback controls (play/pause, frame forward/backward) locate the point on the media’s timeline where you want to begin including gaze data for analysis using dynamic AOIs. In this case, just a few frames in from the beginning of the video.
  3. Draw an AOI around the target, here, the sole white horse among a herd of brown horses. Doing so will place a keyframe marker the same color as the AOI onto the timeline. Using the playback controls, step forward until the horse has moved such that it is now beyond the boundaries of the AOI as defined in the first keyframe. Make sure you switch from AOI-drawing to AOI-editing mode in the toolbar and then drag the AOI to encompass the horse in entirety again. If the object has changed in size or shape over the course of the tracking movement. Repeat until the last frame where Dynamic AOI-based data inclusion is desired. At this point, click on the “Activation” toggle in the toolbar and set to “Off.” This will insure that only data during the time interval of interest is aggregated. It should look something like in the illustration above. In this example, there are three keyframes because the motion path of the white horse is simple and brief. If the target motion were complex, there could be significantly more.
  4. Analysis proceeds then as with static AOIs on the Statistics tab. Select the media to analyze, the metrics and descriptive statistics of interest, and the participants or participant groups and click on Update to generate the data tables.

Tip: While the Dynamic AOI tool can be used to gather gaze data during the visual tracking of moving stimuli, be careful with the judgments made from the resulting data. If the object motion is large scale, smooth, and fast, then most likely the following eye motions will smooth pursuit instead of saccadic in nature. In this case, while total looking time to the target would still be valid, fixational measures would probably not make much interpretive sense.

Tip: For many applications, the AOI size may not change as the target moves or translates across the frame. However, if you dynamically resize an AOI across target motion, remember to keep in mind the selectivity and sensitivity considerations on AOI sizing that were explained in last month’s blog entry.


The Dynamic Areas of Interest tool is a powerful function provided in Tobii Studio for the analysis of linear dynamic stimuli such as movies and animations. Using dynamic AOIs, you can bring the full power of eye tracking statistics and automated AOI analysis to your moving stimuli.

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