Freiburg Vision Test (‘FrACT’)
Freiburg Vision Test (‘FrACT’)
For quality results be sure to observe the following
- Calibration to the screen resolution: enter the length of the blue ruler in millimenters on the Settings screen
- Distance observer–screen: enter in centimeters on the Settings screen (and be sure it's large enought to avoid ceiling effects, see Manual [PDF])
- Luminance of the visual display unit. DIN-ISO prescribes a range 80–320 cd/m², easy to achieve with current display units. Surround not darker than 1% of the screen luminance (if the screen ≥ 10°; if smaller, then between 10% and 25%).
- Luminance linearity of your display unit
- For acuity: not very important. Ignore, or go to
Settings>Luminance linearisation and use to top two buttons for approximate linearisation.- For Vernier: semi-important. Perform the psychophysical 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 in the box at
Settings>Luminance linearisation>gamma value.- Switch off keyboard repeat
This avoids prolonged pressing of a key causing unwanted responses. How to do this:
- Mac OS X: System Preferences>Keyboard>Keyboard>Delay Until Repeat “Off”
- Windows XP (English): 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”.
[Yes, it does not make sense in German – automatic translation?]- If you want to export results to a spreadsheet
- Select the correct decimal sign for your locality in Settings
- 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
- If you are using a remote keypad for response entry: make sure it is oriented correctly
- Run a binocular trial run with your subject. If understood, you can stop early. 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]
- More ideas? Suggestions welcome.
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