Freiburg Visual Acuity & Contrast Test

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 only 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 the Manual [PDF]. If “max. VAdecimal” and the numbers around it do not turn red, you’re safe. This setting is saved by FrACT.

Luminance of the visual display unit
DIN and ISO norms 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 automatically 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.
You can also use a screen calibrator to set the system to another gamma value (e.g. 1.8); if so, then enter that value in FrACTs gamma box.

Switch off keyboard repeat (otional)

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

Export results → 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 (⌘-tab for Macs, alt-tab for Windows)
After each test run, switch to the spreadsheet and paste (⌘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]

Freiburg Vision Test (‘FrACT’)

Checklist

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

→FrACT homepage

	Created: 2011-02-16. Last change: 2019-08-21 by Michael Bach
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