Hi,
> No no, to take the average of the areas is not the same as take the average
> of the coordinates, because the areas depend quadratically on linear
> distances. An average of the areas would not necessarily represent a surface
> at the middle, most likely representing an (invisible) surfac
Hi Boris,
For now I am taking the geometric average between pial and white
surface coordinates.
Is that the right way to do it, or is there a more precise way?
To obtain a surface that lies in the geometric middle between white and
pial surfaces, it is correct to take the average of the coor
Hi Bruce and Doug,
thank you both so much for your help.
>> You could generate it yourself easily enough
>> though.
For now I am taking the geometric average between pial and white surface
coordinates.
Is that the right way to do it, or is there a more precise way?
Also: If I decided to repr
Yes, the avg.area files have the average over the input subjects at each
vertex. I've used it to overcome this problem.
doug
On 5/12/11 8:04 AM, Bruce Fischl wrote:
> Hi Boris,
>
> 1. Doug can say for sure, but I believe so.
> 2. No. The mid surface doesn't correspond to any boundary in the image
Think in 2D about averaging two sine waves that are shifted 90 degrees
from one another.
The length of of the resulting line will be far less than that of either
curve.
On 05/11/2011 11:20 PM, Michael Waskom wrote:
> Hi Bruce,
>
> I've seen this brought up on the list a few times, and, I have t
Hi Boris,
1. Doug can say for sure, but I believe so.
2. No. The mid surface doesn't correspond to any boundary in the image and
so we are always hesitant to provide any morphometric measures for it. We
are working on a more explicit estimation of the location of layer IV, but
that is a future
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
Hi Bruce,
Thanks a lot for your reply.
> 2. The surface area of fsaverage is less than any individual, so you
> *definitely* don't want to use it. You should map the ROI back to individuals
> and compute it in the native space.
I have two follow-up questions:
1) Do .pial.avg.area.mgh and/or
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
Hi Boris
1. That's fine.
2. The surface area of fsaverage is less than any individual, so you
*definitely* don't want to use it. You should map the ROI back to
individuals and compute it in the native space.
cheers
Bruce
On Wed, 11 May 2011, Boris Bernhardt wrote:
> Hello Freesurfer-experts,
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