Freiburg Vision Test (‘FrACT’) 

by Prof. Michael Bach – Checklist

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To achieve high-quality results you will have to be knowledgeable in sensory testing and want to observe the following:

• Calibration to the screen resolution
  Enter the length of the blue ruler on the Settings screen (in millimeters). This is saved by FrACT and needs to be repeated when changing screens or resolution.
• Distance observer–screen
  Enter on the Settings screen (in centimeters), and be sure it's large enough to avoid ceiling effects, see Manual [PDF]. If “max. VAdecimal”  does not turn red, you're safe. This is saved by FrACT.
• Luminance of the visual display unit
  DIN-ISO prescribes a range 80–320 cd/m² , easy to achieve with current display units
• Luminance of the surround
  The surround requirements depend on screen size. If screen ≥ 10°: not darker than 1% of the screen; for smaller screens: between 10% and 25% of screen luminance.
• Luminance linearity of your display unit (setting saved by FrACT)
  • For acuity: not very important. Ignore, or go to
    Settings>Luminance linearisation and use the top two buttons for linearisation
  • For Vernier: semi-important. Perform the simple calibration mentioned above
  • For contrast threshold: very important. Best to use a screen calibrator (these have become very inexpensive, e.g. Datacolor's Spyder), calibrate the screen to a gamma=1.0, and enter that gamma value of 1.0 in the box at
    Settings>Luminance linearisation>gamma value.
• Switch off keyboard repeat  
  
  This avoids unwanted responses, caused by prolonged pressing of a key. How to do this:
   
  

  • Mac OS X:
    System Preferences>Keyboard>Keyboard>Key Repeat “Off”
  • Windows XP (English):
    Start>Control Panel>Accessibility Options>Use FilterKeys
    Tick it, go inside and tick “Ignore repeated keystrokes”
  • Windows XP (German):
    Einstellungen>Systemsteuerung>Eingabehilfen>Anschlagverzögerung verwenden
    Tick this checkbox, then go inside and tick “wiederholte Tastenanschläge ignorieren”
  • Windows 7: Start>Control Panel>Keyboard: Repeat delay “long”, Repeat rate “slow”.
    To turn it off completely, you need to go to
    Start>Control Panel>Ease of Access>Set up Repeat Keys…>Ignore all repeated keystrokes
• If you want to export results to a spreadsheet  
  • Select the correct decimal mark (comma or period) for your locality in Settings, bottom right. (Important, otherwise Excel might interprete your results as dates!)
  • Decide whether you only want the final result or the full history (with reaction times etc.) and select in Settings
  • Start the spreadsheet program (e.g. Numbers or Excel) beforehand, add additional information you might want and switch between FrACT and spreadsheet with the task switcher shortcut (cmd-tab for Macs, alt-tab for Windows)
  • After each test run, switch to the spreasheet and paste (cmd-v for Macs, ctrl-v for Windows)
• If you are using a remote keypad for response entry: make sure it is oriented correctly
• Run a binocular training run with your subject. While doing this, you can explain the “forced choice” situation, e.g.: “use your best guess, even if you don't see it!”
• Whenever the subject reports “whoops, pressed the wrong key” during the first 3 trials: Abort by pressing “5” twice and restart this run
• Much more detail in the Manual [PDF]

 

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