FAQ: Why are my stimuli not visible in Data Viewer's Spatial Overlay View?
There are three main reasons why stimuli such as text and images are not visible in Data Viewer's Spatial Overlay View, and you only see fixations on a black background, as in the image below:


  1. You have not set an Interest Period: The Spatial Overlay view displays all the gaze data from the entire trial overlaid on top of the last display image that the participant saw during in the trial. In many experiments the trial will end with a blank screen, so this is what is displayed in the Spatial Overlay View. The solution is to set an Interest Period that defines the duration that the stimuli of interest were on screen Periods. Please see Section 6.4 of the Data Viewer User Manual or this FAQ for detailed instructions on setting Interest Periods. In brief:

    • In the main Data Viewer toolbox click on the drop down menu where it says ""Full Trial Period"". Then click the ""Edit ...."" option.
    • When the Interest Period Manager appears click the New Interest Period button (top left button). Then give it a label (e.g., StimulusOnly).
    • Enter the Message Text that was sent out by your experimental script when the stimuli was drawn to the screen - for example "Display_Sentence". Please note that messages are case-sensitive.
    • Enter the Message Text was sent out by your script for the subsequent or final stimulus (e.g., Display_Blank). Alternatively set a fixed duration.
    • Close the Interest Period Manager.

      Now only the data (and the corresponding image) for that part of the trial will be displayed in the various views of Data Viewer, including the Spatial Overlay View.

  2. You have moved the results folder or individual EDF files from their original location: EDF files do not actually contain any of the resources that Data Viewer uses to present the visualization (such as image or video files presented during the trial, or Interest Areas defined within Experiment Builder). Instead, they contain messages which are pointers to where these resources are actually stored relative to the location of the EDF file. If EDF files are copy to another computer or if files and / or folders are renamed, the links between the files will be broken, and Data Viewer will not be able to display any of the trial visualization, and only the gaze data will be presented over a black background.

    If you need to analyse your data on another computer, please copy the entire deployed project folder (which includes the EDF files) to the new location. That way, the links to the trial resources in the EDF files will be preserved. Alternatively, you can load your EDF files into a single Data Viewer viewing session on the original computer, and then use the File menu -> ""Package ..."" command to create a single DVZ file that will contain all the data and trial resources. Move that file to the other computer and then either double-click on the DVZ file to launch Data Viewer (which will prompt for a location to unpack the viewing session) or use the File menu -> ""Unpack ..."" command on the new computer from within Data Viewer.

  3. The Viewing Session (EVS file) has been moved from its original location: The EVS file does not contain all the information required to recreate a full viewing session. To move the Data Viewer Viewing Sessions to another computer, please use the File -> Package function to create a single DVZ file, and copy this file to the new location and then unpack it. This way all necessary dependency files (such as the trial images / Interest Areas) will be incorporated.
The simplest way to determine which of the above issues is causing the black background / lack of trial stimuli is to switch to Animation Playback View, and start the playback. If images appear during the playback then it most likely issue 1, and setting an Interest Period is required. If no images / videos appeared, then it most likely to be issue 2 or 3.