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Subject:

Re: exclusive mask in 2nd level analysis

From:

Gail O'Kane <[log in to unmask]>

Reply-To:

Gail O'Kane <[log in to unmask]>

Date:

Tue, 20 Jul 2004 14:02:36 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (86 lines)

Hello all:

The explanation given below about using inclusive and exclusive masks is very
helpful. Could someone assist me with a few followup questions to that email?

1) I am trying to compare 2 groups and use inclusive masking to see where
activations are common to the 2 groups and exclusive masking to see where they
are different. Is this concept and the method described below by Tobias Egner
suitable for this purpose?

2) How do I "write image" (as mentioned below) and what is the name of the
file that it writes?

3) What is the output file name from the ImCalc operation? is this what I choose at
the prompt "explicitly mask images"?

4) Will SPM prompt me for the t-value threshold mentioned below, at the ImCalc
stage or at the "explicitly mask images" stage?

Any help would be greatly appreciated.

Gail O'Kane
MIT


On Thu, 18 Mar 2004 11:30:35 -0500, Tobias Egner <
[log in to unmask]> wrote:

>Dear Jeong,
>
>If you want to apply an exclusive mask at the group analysis do the
>following: Conduct group analyses (e.g. One-sample t-test) for the contrast
>that you want to use as an exclusive mask. When you have done your
>t-contrast, save the resulting image ("write image"). Then use the "ImCalc"
>button to convert this saved image into an inclusive mask by using the
>function (i1&gt;t), with t being your chosen t-value threshold. In order to
>turn this into an exclusive mask, select ImCalc again, take your inclusive
>mask and apply the function (i1-1).*(-1). This gives you an exclusive mask
>which you would then use as an "explicit mask" in the estimation process of
>the group contrast that you want to be masked.
>
>Good luck,
>
>Tobias.
>
>Tobias Egner, PhD
>fMRI Research Center
>Columbia University
>Neurological Institute, Box 108
>710 West 168th Street
>New York, NY 10032
>
>Ph: 212 342 0121
>Fax: 212 342 0855
>-----Original Message-----
>From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On
>Behalf Of Jeong Bum Seok
>Sent: Thursday, March 18, 2004 1:22 AM
>To: [log in to unmask]
>Subject: exclusive mask in 2nd level analysis
>
>Dear SPM experts
>
>I'm a beginer.
>Although my question is obsolete, I'd like to get advance due to your help.
>My question is the way of exclusive mask in 2nd group analysis.
>
>In individual analysis, i got images using specific contrast.
>and after using exclusive mask option I found slightly different images in
>graphic window.
>But in group analysis (one sample t-test), i don't know how i can get
>latter image (acquired with mask option).
>I just found the explicitly mask option after selected several con*.img.
>
>
>My question is like below
>firstly, in individual analysis, if i selected exclusive mask option, the
>result files are different from image without exclusive mask option?
>sencondly, How can i use exclusive mask option in group analysis?
>thirdly, explicitly mask option in group analysis is different from
>exclusive or inclusive mask option in individual analysis?
>
>BS Jeong
>Eulji medical university
>Korea

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