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Working with dynamic stimuli in the AOI tool

Working with dynamic stimuli in the AOI tool

Tobii Pro Studio Tobii Pro Lab Areas of Interest

Learn more about and get some tips on how to work with AOIs on moving stimuli like movies or animations in Tobii Pro Lab and 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 test subjects that have been exposed to the same video stimulus (linear dynamic recordings)
  2. Dynamic AOIs can be used to aggregate data for multiple test subjects that performed a web- or screen recording- based task, or a glasses recording (nonlinear dynamic recordings). However, in order to aggregate the data from all recordings, one has to create individual AOIs on the video of each recording, and use AOI Tags (Pro Lab) or Groups (Pro Studio) to merge the data.
  3. Dynamic AOIs can be turned on and off, moved, and resized to track the targets of interest
  4. Dynamic AOIs can’t be used for static stimuli like images

First, let’s define the two different kinds of dynamic stimuli. Linear dynamic stimuli 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. Every recording performed with that video will be associated to it, so once you define your moving AOIs on it, the data will be automatically aggregated.

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.

An additional consideration that can affect your choice of tools in Pro Studio is the whether the target of interest on the linear dynamic stimuli  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. 

Watch a tutorial

Learn how to create a dynamic AOI in Pro Lab by watching the video above or by following the instructions below. You can also try it in Pro Studio by following the instructions in the next section.

Try out the Dynamic AOI tool in Pro Lab and Pro Studio

Let's get started! Much of the detail about the use of the tool can be found in chapter 8 of the Pro Studio and Pro Lab User Manuals, 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 a few participants.

In Pro Lab: 

  1. Go to the  AOI tab (AOI tool) in Pro Lab and select the stimulus on the "Media Selection" panel.
  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-Draw to AOI-Select 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 “AOI Active” toggle in the toolbar and set to “Off”. This will insure that only data during the time interval of interest is aggregated. In our video example, the number of key frames that are generated are low 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 Metrics tab. Select the metrics, recordings, time of interest (media) and Areas of interest to analyze and click on "Export" to generate the export file.

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 are explained in article Digging Into Areas of Interest

In Pro Studio:

  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. In our video example, the number of key frames that are generated are low 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 are explained in article Digging Into Areas of Interest

Conclusion

The Dynamic Areas of Interest tool is a powerful function provided in Pro Studio and Pro Lab for the analysis of dynamic stimuli such as movies, animations, and other types of video recordings (e.g. glasses). 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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