<div dir="ltr">Hi Eric and Alex,<div><br></div><div>Now I think understand why the sign flip affects the source-level results within a ROI.</div><div><br></div><div>Thanks again, Eric! That's exactly what I want to know. So I'll morph all subjects to the same space first, and then conduct any ROI-based statistical analysis on the sign flipped values?</div><div><br></div><div>Thanks!</div><div>Lin</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, May 31, 2017 at 9:56 AM, Eric Larson <span dir="ltr"><<a href="mailto:larson.eric.d@gmail.com" target="_blank">larson.eric.d@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><span class=""><div dir="ltr"><div>In all examples the sign flip is not data dependent.<br></div></div></span><div class="m_2110138219259462846m_6712086309811178845gmail-HOEnZb"><div class="m_2110138219259462846m_6712086309811178845gmail-h5"><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div><div><div><div><br></div><span class="">Then do we need to worry about the signs when averaging across subjects? Or do I misunderstand something?<br></span></div></div></div></div></blockquote></div></div></div></div></blockquote><div><br></div><div>Just want to add that, although the flip does not depend on the MEG data, it does depend on the MRI data. Because the flip sign is arbitrary and subject cortical geometries vary, the effective direction and sign can change on a subject-by-subject basis. So one option is to morph all subjects to the same space (e.g., to fsaverage ico-5) and do the sign flipping on an identical source space. You lose some of the geometrical accuracy of the sign flipping, but the alignment direction and sign flipping should then be identical across subjects.</div><span class="HOEnZb"><font color="#888888"><div><br></div><div>Eric</div><div><br></div></font></span></div></div></div>
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