[Mne_analysis] Signs of source solutions with fixed orientation

Ying Yang evergreenlifeyangying at gmail.com
Fri Aug 15 02:19:26 EDT 2014
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Hi MNE community,

I was working on a source localization method, and I observed this sign
issue when I did a simple simulation.
I simulated a waveform for an ROI in the left auditory cortex
("left_aud_dipoles.png"), with a fixed orientation (normal direction),  but
using MNE,  some of the waveforms of the dipoles in that ROI had flipped
signs. (see "truth_left_aud.png" and "mne_left_aud.png", near time 0 ms).
I learned that this is common because of the sulci or gyri structure.
But is this also common in simulations? Is it inevitable?
If this is true, when I measure the  error of the source solution,  should
I flip the signs or take the absolute values before comparing with the
truth?

Thanks a lot.
Best,

Ying
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