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FAQ: How can I see the participant's gaze overlaid on the stimulus during data collection?
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Joined: Sep 2020
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#1
09-02-2020, 08:11 AM
When recording gaze data, the participant's current gaze position is displayed in real-time on the Host PC screen. To provide context for the real-time gaze position you can transfer an image, a primitive representation of the stimuli, or draw some simple shapes to act as a background. The three approaches are illustrated below.

   


  1. Transferring a static image to Host PC:

    Make sure that a PREPARE_SEQUENCE action node precedes the Recording Sequence that contains the trial events and checked the "Draw to EyeLink Host" property of to "IMAGE".
       

    Within the Recording Sequence, check the "Use for Host Display" property within the DISPLAY_SCREEN node to transfer to the Host PC. Only one Display Screen can be transferred and only the last Display Screen image will be transferred if multiple display screen nodes have this property checked.
       

    Note, that all the screens will be displayed in Data Viewer in the Spatial Overlay View and all images and videos will be displayed as it did during the experiment in the Trial Animation Playback View. Additionally, if the Display Screen transferred to the Host PC contains a video, only the first frame of the video will be transferred to the Host PC and displayed.

  2. Drawing "primitive" shapes to the Host PC: This option (shown in the centre image above), allows for basic shapes to be draw on the Host PC display. For example, if an experiment is showing two images side-by-side on the Display PC the Host PC will show two open boxes at the locations of the images. It provides an outline of the resources used in the selected Display Screen. To use a primitive image, follow the instructions above,  but set the Prepare Sequence's Draw to Eye Link Host property to PRIMITIVE. This mode can be useful the images are interfering with the abilty to see the gaze cursor on the Host PC recording s creen.

  3. Using drawing commands: With complex stimuli types or moving elements it may be easier to represent the stimuli or areas of interest on the Host PC with simple shapes. For example in a smooth pursuit task (show in the right image) the horizontal and vertical target trajectories  are indicated by lines with small squares marking the limits. The Pursuit project bundled with Experiment Builder Examples provides an example of how to send drawing commands to the Host PC from an Experiment Builder script in its DRAW_FEEDBACK_GRAPHICS_TO_HOST sequence.

    All of the drawing commands are also documented in the "COMMANDS.INI" file which can be found in the /EYELINK2/EXE (for EyeLink II) or /ELCL/EXE (for EyeLink 1000, EyeLink 1000 Plus) folder of the host partition. To access the COMMANDS.INI file use either the File Manager on the Host PC or it can also be access via a web browser on the connected Display PC through the address 100.1.1.1 when the Host PC is in the File Manager mode.