Hello!
Our lab use 24 channel EEG system, and we record EOG from vertical and horizontal EOG (VEOG / HEOG) from the right eye using bipolar and monopolar montages. EEG and EOG signals referenced to A1 online.
I'm not sure what is the proper label for those two VEOG and HEOG channels and EOG bipolar channel in the channel location file to be recognized.
My question is, what's the location values (X, Y, Z sph_theta, sph_phi, sph_radiu) in the ".loc" file for VEOG, HEOG, and bipolar EOG?
Thank you in advance!
A description of the values can be found here: http://atonal.ucdavis.edu/resources/docs/matlab/public/eeg/fixes/readlocs.html
'X' [real] Matlab-Cartesian X coordinate (to nose)
'Y' [real] Matlab-Cartesian Y coordinate (to left ear)
'Z' [real] Matlab-Cartesian Z coordinate (to vertex)
'sph_theta' [real degrees] Matlab spherical horizontal angle; positive = rotating from nose (0) toward left ear.
'sph_phi' [real degrees] Matlab spherical elevation angle;
positive = rotating from horizontal (0) upwards.
'sph_radius' [real] distance from head center (unused)
Maybe there is a default location value for these electrodes, but it will not be accurate because it is generally not attached to the cap and the position might thus vary a lot between people.
A good way to accurately estimate the location of these electrode is to use the polhemus or captrack numerization of the electrodes positions.
Just to add to the previous answers (that I fully agree with): how precise the estimates of these electrode locations should be depends a lot on the preprocessing steps/analyses you want to perform. Most researchers end up disregarding EOG channels (including their spatial location) anyway for processing steps like ICA, spatial filtering, source localization, and generating scalp plots. If this is the case for you, you can just provide rough estimates of the coordinates (or really even completely random ones), since the EOG locations are never really used.
See this link
https://github.com/openroc/eeglab/blob/master/tags/EEGLAB7_0_0_0beta/plugins/dipfit2.2/standard_BESA/standard-10-5-cap385.elp#L357
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