EEG Channel projection

Hi All

In other signal processing fields, such as the earth sciences (my background is geophysics) it is reasonable and common to take a spherical coordinate system and related raw signals and project them onto an appropriately chosen 2 d plane to support analysis. Examples may include mapping seismic data recorded on the surface of the earth.

Is it clinically reasonable to map EEG channel data in a similar way such as mapping montages that cross the naison/inion plane onto the naison/inion plane?

If it is reasonable then are there standard methods for doing so?

Thank you and regards

Robert

Hello @robkoneksa,

are you suggesting to plot a sensor that is located “below” the Nasion-Inion plane in 3D space by orthogonally projecting it onto this plane, thereby placing it closer to the center of the circle formed by the Nasion-Inion plane?

Hi Richard

Thank you for your prompt response.

To answer your question - Yes

Though i am first asking if this is an appropriate thing to do from a clinical perspective. Different montages may cover different parts of the brain and I don’t know enough to know if it is reasonable to treat the brain as a homogenous entity from a signal processing perspective.

On the other hand when working with vectors in other physics problems such projection is quite common - i.e determination of a vector’s contribution to each of the axes in the target coordinate system.

Regards

Robert

Hello @robkoneksa,

when MNE produces the 2D projections, sensors below the Nasion-Inion plane are moved farther away from the head circle center. I believe this makes the most sense and provides reasonable interpretability.

Of course, avoiding such a dimensionality reduction altogether is probably the cleanest way to deal with the data … hence, I suggest you also take a look at the plot_field() method of evoked objects, which I believe is an awesome way to visualize the data without having to worry about the question of how to best project 3D to 2D … that is, if you have evoked data. :sweat_smile:

Best wishes,
Richard

cool - that I didn’t know. Thank you very much. I took a read through the docs and am struck how similar the plot in the MNE plot_field method at:

https://mne.tools/stable/auto_tutorials/evoked/20_visualize_evoked.html

looks a lot like vector projects used in the earth sciences such as this one for polar atmospheric flow. In the earth sciences people use a library called NCAR.

thank you for your help.

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