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Hi Sanghyun,
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<div>Although the ‘perceived SNR’ may change when applying the leadfield correction, it is simply biophyisically incorrect, if you DON’T do it.</div>
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<div>The reason is the following:</div>
<div>If you remove a component from your channel data, what happens is that each of the resulting EEG/MEG channels reflect the potential difference/magnetic field strength as measured by a referenced electrode or a magnetic field pickup coil at a specific location
in space, <i>minus</i> a weighted combination of potential differences/magnetic field strengths measured at all other locations (where the weighting is given by the spatial topography of the component). In other words, you apply an intricate re-referencing
scheme/create a complicated synthetic gradiometer sensor. When building your forward model (a.k.a. leadfield), the purpose is to build an accurate model of the spatial distribution of potential differences/magnetic field strengths given what your channel leveld
data represents. Since it now represents this re-rereferenced data/synthetic gradients, it needs to be accounted for in the model.</div>
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<div>Best,</div>
<div>Jan-Mathijs</div>
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<div>On Feb 15, 2016, at 3:57 AM, Sanghyun Lim <<a href="mailto:santagravity@gmail.com">santagravity@gmail.com</a>> wrote:</div>
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<div class="gmail_default" style="font-size:12.8px">Dear fieldtripers,</div>
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<div class="gmail_default" style="font-size:12.8px">I recently read a hipp's 2015 paper <span style="font-family:arial,sans-serif">which asserts that do not modify leadfields after ICA artifact rejection since it could decrease the estimated source SNR.</span></div>
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<font face="verdana, sans-serif"><a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121048" target="_blank">http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121048</a></font></div>
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But by seeing ft_rejectcomponent, fieldtrip recommends modifying leadfields after ICA.</div>
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Is there a specific reason to do this?<br>
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thanks in advance</div>
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Sanghyun.</div>
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