Knowledge Base

How Participant Calibration Works

If you use images for calibration, FaceReader searches for the image with the lowest model error. If you use camera or video analysis, FaceReader analyzes two seconds and uses the image with the lowest model error for calibration.

Correcting Expression Intensities

FaceReader corrects each expression other than neutral in the following way:

Corrected Expression intensity = max (0, (I_a - I_c))/ (1-I_c)

Where I_a is the intensity of that expression in the analysis and I_c is the intensity of that expression found in the calibration. If (I_a - I_c)/ (1-I_c) is lower than zero, the calculated expression intensity will be zero.

You can find the I_c values in the header of the Detailed log file.

Correcting The Intensity Of Neutral

The intensity of Neutral is calculated in the following way:

Corrected Intensity Neutral = (N_a + (1- I_max)))/2

Where N_a is the intensity of Neutral classified by FaceReader and I_max is the intensity of the expression with the highest intensity, excluding Neutral and Contempt.

Example

Consider the following expression intensities:

• Neutral = 0.6
• Happy = 0.9
• Sad = 0.1
• Angry = 0
• Surprised = 0
• Scared = 0
• Disgusted = 0

This gives an I_max of 0.9

And a corrected intensity of Neutral of:

Corrected Intensity Neutral = (0.6 + (1 - 0.9)) / 2 = 0.35

Continuous Calibration

Aim

To correct for person-specific biases in facial expressions if you do not have images during which the test participant looks neutral.

Procedure

1. Open the analysis for which you want to use continuous calibration. To open an analysis, double-click it in the Project Explorer, or click the magnifying glass button next to it.
2. Click the Analysis Settings button at the bottom of your screen to open the Analysis Settings window.
3. Click the pencil button next to Selected Calibration and select None.
4. In the same window, click the pencil button next to Continuous Calibration and select Yes. This sets the Selected Calibration field to Disabled.

Source: FaceReader 10 Reference Manual (Help), Noldus Information Technology