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 (mandatory)
Use the plastic-card method; or measure and enter the length of the blue ruler in Settings>General (in millimeters). This is automatically saved and needs only to be repeated when changing screens or resolution.
Important: After calibration, don’t change the zoom level of your operating system or the browser! (Or recalibrate) Best re-check with the plastic card – you can detect zoom changes of ×1.5 at one glance.
Distance observer–screen (mandatory)
Enter in Settings>General (in centimeters, there’s a conversion to inch). It must be large enough to avoid ceiling effects, see the Manual on this. “max possible acuity” ≙ “min possible LogMAR” must be better than your desired best acuity. This setting is automatically saved.
Luminance of the visual display unit (mandatory)
DIN and ISO norms prescribe the range 80–320 cd/m² (recommended: 200 cd/m²). This is easy to achieve with current display units; most cases: set to near maximum, keeping black black.
Luminance of the surround (mandatory)
No light sources or reflective surfaces seen by the testee should be brighter than the visual display unit. No glare sources (e.g. spotlight, light reflex, any very bright surface) should be within the field of view.
Luminance linearity of your visual display unit (optional for acuity, mandatory for contrast)
- For acuity: not very important. Ignore, or go to
SettingsGammaand use the ± buttons as explained there. - For Vernier: semi-important. Perform the simple calibration above.
- For contrast thresholds: very important. Best use a screen calibrator (these have become very afforadble, e.g. Datacolor’s Spyder [must be the “Elite” or better if gamma 1.0 desired]), then …
- either use the screen calibrator to measure current gamma, or set to your preferred gamma value (e.g. 2.0). Then enter this value in FrACT’s gamma textbox.
- or calibrate the screen to a gamma=1.0, and enter that gamma value of 1.0 in
Settings>Gamma.
- This setting is automatically saved.
Start with a binocular training run (suggested)
Running a binocular training run with your prticipants has proven useful. They can familiarise themselves with the test, and you can explain the “forced choice” situation, e.g.: “use your best guess, even if you don’t see it!” Usually, I don’t even analyse the results of this run.
Remote keypad for response entry (suggestion)
- This is incredibly useful!
- If you are using a remote keypad for response entry, make sure it is oriented correctly :). Really.
Switch off keyboard repeat (suggestion)
This avoids unwanted responses, caused by prolonged pressing of a key. Use your operating system’s keyboard options to do this.
Semiautomatic export of results → spreadsheet (optional)
- Select the correct decimal mark (comma or period) for your locality in
Settings>General, bottom left. (Important, otherwise the spreadsheet might interprete your results as dates!). In FrACT₁₀ the default is “automatic”, that should be sufficient. - Decide whether you only want the final result or the full history (with reaction times etc.) and select in
Settings>General. - Start the spreadsheet program (e.g. Excel, LibreOffice, or Numbers) 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. Voilá!
More export options in the FrACT₁₀ Manual.
“Whoops, pressed the wrong key”
When the subject reports “whoops, pressed the wrong key” during the first 3 trials: It’s best to abort by pressing “5” twice and restart this run.
RTFM
Much more detail here: FrACT₁₀ Manual or FrACTclassic Manual [PDF].