Configuring Pro Lab to record eye movements on physical scenes and objects

Tobii Pro Lab Screen Based Eye Trackers Tobii Pro X3-120

The Scene Camera Projects allows Pro Lab to support studies where subjects observe or interact with stationary physical scenes or objects. These types of study provide a stronger immersion experience to the subjects and improve the ecological validity of the findings, than studies that use a 2D stimulus presentation on a screen (Tonkin et al. 2011 – use of physical shelves vs. images of shelfs in packaging design studies; and Woods et al. 2010 – investigating infant object representation with 3D physical stimuli). On the other hand, the setup is more complex than a standard screen based study, as it requires extra configuration steps with the eye tracker and the inclusion and configuration of an external scene camera to record the scenes and objects.

The table below summarizes a few of the factors you need to consider before deciding to use a scene camera setup.

  Screen based image or video - 2D Scene camera with physical scene - 3D Glasses with physical scene - 3D
Setup process automatic (with native or supported screen sizes) manual automatic
Accuracy higher lower higher
Precision depends on tracker depends on tracker high
% of population that can be tracked higher higher lower (does not fit on small infants heads)
Ecological validity & immersion lower higher higher

Prepare your eye tracker, external scene camera and stimulus presentation setup:

  • Make sure that your physical setup is correctly assembled and roughly at the correct distance to the eye tracker. Use the following information in the eye tracker user manual to guide you in this step… – 1) Use the maximum screen size information to help you determine what is the maximum area size that the eye tracker can track if it is mount just below that area – this is your distance “0”; 2) Use this “maximum area size“ as a frame of reference when positioning the eye tracker at the right distance. If your scene doesn’t fit the “frame”, increase the distance of the eye tracker to the scene, until it will. Once you achieve this your eye tracker will be close to the correct position. You will fine tune the distance later when you test your setup by performing a recording in Pro Lab with a subject.
  • Include a calibration board and targets. Make the board as large as your setup (display area). The calibration board can help you physically visualize the plane where the gaze data will be mapped to, as well as facilitate the measurements when you are configuring the eye tracker using the Eye Tracker Manager configuration tool. Choose calibration targets that the test subjects can attend to and fixate accurately.
  • Configure your eye tracker using the Eye Tracker Manager or Eye Tracker Browser. To learn how to do it click on the following link: Configuring the eye tracker with a "non-standard screen" or physical scene.
  • Position the external camera as close as possible to where the head or line of sight of the subject to minimize any parallax effects (e.g. just above the head of the subject or on the side close to the subject’s head at eye level, see sample image below). Connect the camera to the computer and install the necessary drivers and software. Using the software provided by the manufacturer disable any auto settings (such as zoom, focus etc.).
Ipad/Devices Testing with Tobii Pro Mobile Device Stand

Figure 1. In this example of a scene camera setup, the external camera is located close to the line of sight of the test subject.

Prepare your Pro Lab scene camera project

  1. Start Pro Lab and create a new scene camera project. The project overview window opens.
  2. In the “Project overview” window click on the Record tab, the record area is displayed.
  3. Setup the devices you want to use during the recording by clicking on the respective cards - “Eye Tracker” and “Scene Camera”- and selecting the correct devices on the drop-down lists. Once you select the scene camera the image feed is displayed in the Record area.
  4. Using the image of the video evaluate if you need to make any adjustments to the scene camera settings (zoom, brightness or focus) and positioning (i.e. your physical setup is correctly covered by the field of view of the camera). 
  5. Setup your display area by dragging the “Mapping markers” over the image. Make sure the area defined by the markers is the same size of the area entered in the eye tracker configuration tool (Eye Tracker Manager). This can be done by using the calibration board as your visual reference.
  6. Drag the “Calibration markers” in Pro Lab, so that they match the location of your physical calibration markers. You must use a minimum number of two markers.
  7. Lock all the markers by clicking the padlock icon.
  8. Perform a few recordings to test your setup.
  9. Make the necessary adjustments according to the calibration and recording feedback (e.g. adjust your “display area” in Pro Lab if the calibration feedback shows large diagonal systematic errors towards the center or periphery of your setup, or using the Eye Tracker Manager, adjust the eye tracker configuration (distance or height) if you lose tracking when your test subject looks towards the top of your “display area”.
  10. Once you have troubleshot your setup you are ready to start collecting data.

Scene camera project overview

Check out the video and get an overview of the setup process and subsequent data analysis options.

References & Recommended Reading

Tonkin, C., Ouzts, A.D. & Duchowski, A.T. (2011). Eye Tracking Within the Packaging Design Workflow: Interaction with Physical and Virtual Shelves. Proceeding
NGCA '11 Proceedings of the 1st Conference on Novel Gaze-Controlled Applications. May 26-27, 2011, Karlskrona, Sweden.

Woods, R. J., Wilcox, T., Armstrong, J., & Alexander, G. (2010). Infants’ Representations of 3-Dimensional Occluded Objects. Infant Behavior & Development, 33(4), 663–671.

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