Purpose: Bring the signal amplitude to a standard level.
Formula:normalized_signal = 5 * signal / mean(abs(signal))
How it works:
- The mean absolute value of the signal is calculated.
- The signal is scaled so that the mean absolute value becomes 5.
Use case: Standardizing amplitudes to compare signals across participants or sessions.
Physiological explanation of normalization:
The amplitude of the EEG signal varies greatly between people and even between sessions for the same person. This depends on:
- Skull and skin thickness
- Quality of electrode contact
- Individual characteristics of the brain
- Level of activation
Why normalization is needed:
- It makes it possible to compare signals between different people.
- It removes the influence of technical factors (contact quality).
- It focuses attention on patterns rather than absolute values.
- It simplifies visualization (all signals are displayed on the same scale).
Important to understand:
- Normalization does not change the shape of the signal, only its scale.
- Relative changes are preserved.
- Absolute values are lost (a normalized signal cannot be directly compared with a non-normalized one).