View Categories

7.4. Emotion Calculation Method

1 min read

Table of Contents

7.4.1. Power Computation #

For each electrode and frequency band:

  • Filtering in the selected band is applied.
  • Power is computed in a sliding window:
    window_samples = window_seconds * Fs
    for i = 1:(length(signal) - window_samples)
    power(i) = 1 + log10(sum(signal(i:i+window_samples-1).^2) / window_samples)
    end

Power formula:
power = 1 + log10(mean(signal_window.^2))

7.4.2. Arousal #

Formula:
Arousal = (Electrode1_beta + Electrode2_beta) / (Electrode1_alpha + Electrode2_alpha)

Theoretical rationale: The beta/alpha ratio reflects the activation level of the cerebral cortex. Beta activity is associated with active thinking and stress, while alpha activity is associated with relaxation.

Physiological explanation of arousal:

Arousal is the general activation level of the nervous system, ranging from deep sleep to severe stress.

Neurophysiology of arousal:

Low arousal: alpha rhythm dominates (8–13 Hz)

  • relaxed wakefulness
  • eyes closed
  • meditation
  • calm state

Medium arousal: mixed activity

  • eyes open
  • normal activity
  • alpha/beta balance

High arousal: beta rhythm dominates (13–30 Hz)

  • active thinking
  • problem solving
  • stress
  • anxiety
  • physical activity

Interpretation:

  • Low values (<0.5): low arousal, relaxation, possible drowsiness
  • Medium values (0.5–1.5): normal arousal, wakefulness
  • High values (>1.5): high arousal, stress, active mental work

Clinical significance:

  • Persistently high arousal may indicate chronic stress or anxiety.
  • Very low arousal may indicate depression, fatigue, or drowsiness.
  • Optimal arousal depends on the task (low for rest, medium to high for work).

7.4.3. Valence #

Formula:
Valence = (Electrode2_alpha / Electrode2_beta) - (Electrode1_alpha / Electrode1_beta)

Theoretical rationale: Alpha/beta asymmetry between the left and right hemispheres reflects emotional valence. The left hemisphere (AF3) is associated with positive emotions; the right hemisphere (AF4) with negative emotions.

Physiological explanation of valence:

Valence is the evaluation of an emotion as pleasant or unpleasant. Research shows that the left and right hemispheres process emotions differently.

Theory of hemispheric asymmetry (Davidson, 1992):

Left hemisphere (AF3):

  • processing of positive emotions
  • approach behavior
  • activity, enthusiasm
  • high alpha = low activation = relaxed state with a positive emotional orientation

Right hemisphere (AF4):

  • processing of negative emotions
  • withdrawal behavior
  • caution, anxiety
  • high alpha = low activation = relaxation, but with possible negative valence

Interpretation:

Positive values:

  • the right hemisphere is more relaxed (high alpha/beta)
  • the left hemisphere is more active (low alpha/beta)
  • positive emotions, pleasure, joy

Negative values:

  • the left hemisphere is more relaxed
  • the right hemisphere is more active
  • negative emotions, sadness, anxiety, discomfort

Close to zero: neutral emotions, balance

Important to understand:

  • Alpha activity is inversely proportional to cortical activation.
  • High alpha/beta = low cortical activation in that hemisphere.
  • Low alpha/beta = high cortical activation in that hemisphere.

Practical significance:

  • Positive valence during relaxation is a good sign.
  • Changes in valence reflect emotional responses to stimuli.

7.4.4. Outlier Handling #

Values are clipped at the 95th percentile to remove artifact outliers:
quantile_arousal = quantile(abs(arousal), 0.95)
arousal(abs(arousal) > quantile_arousal) = sign(arousal) * quantile_arousal

The same is done for valence.