Turambar
Software

Virtual Gait Laboratory - Technical Details

The VGL uses simple 3D environments in which to test the subjects. These consist of corridors containing gaps and doors, of various widths, and ninety degree turns. Within these environments the participant is instructed to either walk or stop walking at various times or following a given number of footsteps.

Constructing the Environments

The Quake 4 engine includes a map editor which can be used to create complex environments, as required by today's modern games. Unfortunately the editor has a steep learning curve and requires a significant investment of time to become proficient in its use. Early on in the prototyping of the VGL it became apparent that being unable to quickly create new environments would be a limitation to productivity. To that end it was decided to simplify the process with the creation of the "VGL Environment Generator" (VGLGen).

This simple tool allows map files to be created with a few clicks. The configuration of each map profile is stored in XML format, which can easily be manipulated by hand if required. The data below, for example, is the saved profile from the screenshot above.

<?xml version="1.0" encoding="UTF-8" ?>
<vgl>
    <options>
        <mapname>Demo_Environment</mapname>
        <repeat>50</repeat>
        <ceilingtiles>0</ceilingtiles>
        <floortiles>0</floortiles>
        <width>192</width>
        <height>128</height>
        <length>448</length>
        <narrow>64</narrow>
        <wide>128</wide>
        <doors>0</doors>
        <doortrigger>300</doortrigger>
    </options>
    <stages>
        <narrowgap />
        <widegap />
        <narrowdoor />
        <widedoor />
        <leftturn />
        <rightturn />
    </stages>
</vgl>

Using the "Create .map file" button will generate a Quake 4 format file, which can then be loaded directly into the Quake 4 editor for inspection. Click on the image below for a new window showing a generated corridor in camera and edit modes within the editor.

Specifying the Test Paradigm

The VGL can run various types of test paradigm to measure a subject's ability to respond to "walk" and "stop" cues and to place cognitive load on the brain. The simplest instructions are basic "walk" and "stop" messages presented on screen. More complex tests involve increasing the congnitive load on the subject by asking them to stop or walk based on whether a displayed number is odd or even. Further complexity still can be added by the use of congruent cues (e.g. "BLUE" written in blue) to indicate that the subject should continue walking and incongurent cues (e.g. "BLUE" written in green) indicate that they should stop.

The VGL runs the test using "paradigm files" which describe the cues to be presented on screen. The file below is the one used during the session shown in the video on the main VGL page. The annotated lines in the file have the following meanings:

• Display "WALK" in GREEN and record walking events until 15-20 steps have taken place // (a)
• Display "RED" in RED and record walking events until 25-30 steps have taken place // (b)
• Display "GREEN" in a colour other than GREEN and enter the STOP state for 4-6 seconds // (c)
• Display "WALK" in GREEN and record walking events until 55-65 steps have taken place // (d)

// COLOURS
BEGIN

    WALK 15-20 // (a)
    WALK 25-30 RED // (b)
    WALK 35-45 GREEN
    STOP GREEN INCONGRUENT // (c)

    WALK 55-65 // (d)
    STOP GREEN INCONGRUENT

    WALK 75-80
    WALK 90-95 GREEN
    STOP RED INCONGRUENT

    WALK 110-120
    WALK 125-130 RED
    STOP BLUE INCONGRUENT

    WALK 140-145
    WALK 155-160 RED
    WALK 175-180 BLUE
    STOP RED INCONGRUENT

    WALK 195-200
    WALK 220-225 BLUE
    WALK 240-245 RED
    STOP BLUE INCONGRUENT

    WALK 270-275
    WALK 290-295 GREEN
    STOP GREEN INCONGRUENT

    WALK 315-320
    STOP RED INCONGRUENT

    WALK 335-340
    STOP BLUE INCONGRUENT

    WALK 360-365
    WALK 380 RED
    STOP

END

VGL Software

The VGL is a straightforward modification of the Quake 4 SDK, written in C++. It has a custom main menu to capture the test subject details and to allow selection of the environment to use and the required test paradigm.

Once "Begin" is selected from the menu the game is started placing the subject at the start of the map. From that point on the cues are displayed according to the selected paradigm file. Use of the "left" and "right" controls are all that are required from the test subject; if there is a turn in the map the subject is guided through the turn as they continue to take steps.

When all of the stages specified in the paradigm file have been completed the VGL exits the virtual environment and returns to the menu.

VGL Output

The VGL writes the results of each test run to a CSV file. For each event that occurs the following information is written:

• Elapsed time since the start of the test
• Whether the subject should have been walking at that point
• Event type and sub-event (e.g. step taken, WALK cue displayed, a door opened, subject reached a turn)
• Duration of triggered walk/stop period
• Detail of the type of any prompt displayed
• How many footsteps had been taken up to that point
• How long since the last footstep

It is this raw data that is used and correlated with the brain activity recorded by the fMRI scanner.

Click on the image below for a new window showing a results file loaded into Excel.