[FieldTrip] Pre-processing on orthogonal planar gradiometers?

[Niels Trusbak Haumann]

Dear FieldTrip users. 

I want to detect and remove EOG and ECG by using ICA. My data is from a Neuromag 306 MEG scanner with magnetometers and two orthogonal planar gradiometers. 

I assume that it is recommendable to do the ICA separately on each sensor type separately, i.e. on 1. magnetomers, 2. horizontal planar gradiometers, and then 3. vertical planar gradiometers, because they measure magnetic field changes at different scales and in different directions. 

Would you recommend to do ICA and other pre-processing steps separately on the horizontal and vertical planar gradiometers, or would you just combine the planar gradiometers with ft_combineplanar immediately? 

I'm worried that combining the two different gradiometer sensor types would violate underlying assumptions of the pre-processing algorithms, i.e. ICA, filters and baseline correction, because the planar gradiometer values are only positive valued estimates from the combinations of the original gradiometer measures, which do not seem to have oscillatory deflections around a baseline zero valued point. 

Hope you can help. 

Greetings
Niels.

Niels Trusbak Haumann
M.A. / PhD student
Department of Aesthetic Studies / Center of Functionally Integrative Neuroscience
Aarhus University / Aarhus University Hospital
E-mail: aestnth at hum.au.dk

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