Data import

ASCT currently supports the import of the following file formats:

• EEGlab *.set (EEG),

• Biosemi *.bdf (EEG),

• CTF (MEG),

• ITAB (MEG).

If your format is not on the list it can be converted to one of the above formats using widely available toolboxes.

Channel structure has to be set explicite in order to properly recognize data layout. The numbers below refer to the raw data structure, before any preprocessing.

chan.meeg = [1:64];            % specify EEG/MEG channels 
chan.ref  = [71 72];           % EEG: ref channels to use during import / MEG: ref channels to perform noise balancing
chan.eog =  [65 66 67 68];     % EOG channels for EEG
chan.elec = [65 66 67 68 69];  % electric channels (including EOG)

Actual EEG/MEG channels are to be set with chan.meeg. For EEG, if reference during import is needed, the reference channels have to be set in chan.ref. For CTF (MEG) reference channels are used for noise balancing. EOG channels that pick up oculomotor activity are beneficial for further artifact detection in the case of EEG recording. Provide their indexes in the chan.eog parameter. Finally, chan.elec like ECG (cardiac activity) or EOG can further improve classification of brain components for both EEG and MEG recording.

Electrode positions can be read from file headers (if available), guessed based on electrode names (for the EEG 10-20 system), or provided as an external mat text file in FieldTrip format which name is set in the chan.sensMatFile variable.

Although at the later stages of EEG processing, the signal is re-referenced to average of all scalp electrodes, we recommend linked mastoid refernce at the import. This will help in equating power of electrodes which is optimal for further artifact rejection procedure. We discourage using single electrode (like Cz) as the import reference. If mastoid leads are not available neighbouring sensors at the opposite sides of the scalp can possibly be used.

Format specific notes:

Biosemi: rereferncing is required at the import to ensure optimal SNR

CTF: higher-order gradiometer provided as a refernce can be used for noise balancing procedure that can significantly attenuate recording noise.

% rc.rescaleUnits = 1e15;