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Step 1 - Raw data conversion

Raw signals recorded in continuous or epoch mode have to be converted to the ELAN .eeg file format. These data files should contain signal data and information related to stimulus or response triggers. Several converters are provided for different recording systems: neuroscan2eeg, instep2epeeg, EGIraw2eeg, micromed2eeg, brainamp2eeg, biosemi2eeg, ctf2eeg, neuromag2eeg ...

This conversion will create 2 files with the following extension:
.eeg : contains the digitized continuous signals stored by time-sample and by channel as 16-bit signed integer.
.eeg.ent : is a text header file that should be always associated with the above .eeg file. It contains information such as sampling period, number of channels, electrode names, …

In general, all these information are stored in the original data file created by your acquisition system. However, electrode names and positions are sometimes ambiguously defined and that can corrupt further mapping. The conversion program may thus require a file with the list of electrodes used in your own montage and their coordinates according to the electrode definition system used in ELAN.

In some cases (e.g. brainamp2eeg, biosemi2eeg, ctf2eeg, neuromag2eeg), the conversion program directly creates this file from the original data file, or loads a pre-defined file containing the electrode/sensor names and coordinates in the ELAN system.
For other electrode montages, the user has to create a text file containing the list of electrodes (ordered as in the original data file) in which each line has the following structure:
electrode name '.' electrode number in the ELAN system (see electrode definition in ELAN (elec.dat))

Here is an example for a 32 electrode montage (31 EEG channels and 1 EOG channel): file montage32.elec

electrodes (label)
F3z.71 (electrode name and electrode number separated by '.', according to elec.dat)
F4z.72
F7.13
F3.14
Fz.15
F4.16
F8.17
FT3.48
FC1.40
FC2.41
FT4.49
T3.8
C3.9
Cz.10
C4.11
T4.12
TP3.50
CP1.42
CP2.43
TP4.51
Ma1.85
T5.3
P3.4
Pz.5
P4.6
T6.7
Ma2.86
O1.1
PP13.121
PP24.122
O2.2
EOG.119

The conversion of a Neuroscan continuous file, mydata.cnt, corresponding to this 32 electrode montage, is thus obtained by the following command line:

neuroscan2eeg mydata.cnt montage32.elec myeegfile

with myeegfile being the prefix of ELAN .eeg files created in the current directory (myeegfile.eeg and myeegfile.eeg.ent) corresponding to the continuous signals in mydata.cnt in the current directory. The conversion program will use the montage32.elec to get the specification (name and number in elec.dat) of each electrode.

You may contact us for specific electrode montages.