Mateus,

You raise a good point. 

In practice, it seems that you should keep the uneven distribution of nodes. 
The reason is as follows: If you resample the nodes to a more sparse uniform 
distribution, then you will distort the surface to some degree. The surface 
distortion will inevitable shift the center of gravity. I had thought about 
using the border points of a cluster to calculate the region; however, it seems 
that approach may unequally weight some parts of the cluster if there is an odd 
shape. It might be interesting to do a comparison between these methods.

In the end, it probably doesn't matter how you do the calculation for COG, as 
they should be similar, as long as the method is reported. I should also note, 
a recently accepted article: Cortical network for vibrotactile attention: A 
fMRI study in Human Brain Mapping describes the method and uses the traditional 
method; so there is an established standard that one could rely on and cite in 
future work.

Best Regards, Donald McLaren
=====================
D.G. McLaren
University of Wisconsin - Madison
Neuroscience Training Program
Tel: (773) 406 2464
=====================
This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED 
HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended 
only for the use of the individual or entity named above. If the reader of the 
e-mail is not the intended recipient or the employee or agent responsible for 
delivering it to the intended recipient, you are hereby notified that you are 
in possession of confidential and privileged information. Any unauthorized use, 
disclosure, copying or the taking of any action in reliance on the contents of 
this information is strictly prohibited and may be unlawful. If you have 
received this e-mail unintentionally, please immediately notify the sender via 
telephone at (773) 406 2464 or email.

----- Original Message -----
From: Mateus Joffily <[EMAIL PROTECTED]>
Date: Friday, January 26, 2007 12:12 pm
Subject: [caret-users] ROI center of gravity
To: "Caret, SureFit, and SuMS software users" <caret-users@brainvis.wustl.edu>


> Hi,
> 
> I would like to calculate the center of gravity (COG) of a surface 
> ROI. 
> I see that 'Surface Region of Interest':'Statistical Report' gives me 
> 
> that information. However, if the nodes distribution over the surface 
> is 
> not uniform, the COG is biased toward the more dense regions.
> I understand that, if someone wants to calculate the COG, taking into 
> 
> account the nodes-density, this is the right calculation. But, if I 
> suppose that the surface density is uniform, is there a way of 
> calculating the COG avoiding the nodes distribution effect?
> 
> Thanks,
> Mateus
> _______________________________________________
> caret-users mailing list
> caret-users@brainvis.wustl.edu
> http://pulvinar.wustl.edu/mailman/listinfo/caret-users

Reply via email to