How is arousal calculated?
Arousal indicates whether the test participant is active (+1) or not active (0). Arousal is based
on the activation of 20 Action Units (AUs) of the Facial Action Coding System (FACS). It is calculated with these steps:
1. The activation values (AV) of 20 AUs are taken as input. These are AU 1, 2, 4, 5, 6, 7, 9, 10,
12, 14, 15, 17, 18, 20, 23, 24, 25, 26, 27, and the inverse of 43. The value of AU43 (eyes closed)
is inverted because it indicates low arousal instead of high arousal like the other AUs.
2. The average AU activation values (AAV) are calculated over the last 60 seconds. During the
first 60 seconds of the analysis, the AAV is calculated over the analysis up to that moment.
AAV = Mean (AVpast 60 seconds)
3. The average AU activation values (AAV) are subtracted from the current AU activation
values (AV). This is done to correct for AUs that are continuously activated and might
indicate an individual bias. This results in the Corrected Activation Values (CAV).
CAV = Max(0, AV – AAV)
4. The arousal is calculated from these CAV values by taking the mean of the five highest
Arousal = Mean(5 max values of CAV)