Hi Michael, sure. Partially it's because the way we generate fsaverage is a bit simple-minded as it is only intended for visualization. Each vertex is the average talairach coordinate at that point on the sphere. In general, you can think of averaging as acting as a low-pass filter so that you lose a lot of high-frequency structure. In this case that would mean small, poorly-aligned folds, which means you lose surface area. The average surface is smoother than any of the individuals, and hence has less surface area.
cheers, Bruce On Thu, 12 May 2011, Michael Waskom wrote: > Hi Bruce, > > I've seen this brought up on the list a few times, and, I have to admit, > I've never really been able to wrap my head around it. The naive part of my > brain feel like, if fsaverage is an "average" subject, it should be smaller > than about half of subjects but also larger than about half of them. I'm > sure I'm just not thinking about it quite the right way, but would you mind > unpacking this a little bit? I suspect I'm not the only one for whom this is > somewhat unintuitive. > > Thanks! > > Michael > > On Wed, May 11, 2011 at 6:05 PM, Bruce Fischl > <fis...@nmr.mgh.harvard.edu>wrote: > >> >> 2. The surface area of fsaverage is less than any individual, so you >> *definitely* don't want to use it. >> >> > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
