Approximate time needed to complete the tutorial: max 10 min.
EEG records voltage and voltage is defined as the electric potential difference between two points in an electric field. Therefore, the signal value for each EEG electrode is calculated as the potential difference between the electrode and a reference electrode. Your data will have been created using Cz as a reference which is located in the center of the scalp, because it is the place with the least amount of artifacts (far from neck and facial muscles). Cz, however, is not convenient as a reference electrode, e.g., when plotting topographies of oscillation power plots, because it will appear as if there is almost no activity above the center of the head. Since after computing ICA you will look at spatial topographies of the independent components, you should re-reference your data to a so-called “average reference”. After re-referencing, the potential at a given electrode is given relative to the mean across all channels.
To re-reference your data, click Pre-processing | Find bad channels | Re-reference to average reference (exclude bad channels)
You do not need to save this signal since we don't want to change the RawSignal that is currently stored in the file. You can continue with the tutorial on how to run ICA. Note: if you will run ICA at a later time point, you will need to re-reference to the average electrode again.