Dear Noelia,

I wanted to second Sarika's suggestion.  But I am confused by your response:  "in this region there is no response for unisensory conditions"; if there is no response for either A>0 or B>0, then you don't have a conjunction of (A>0)(B>0)(C>A)(C>B).  So isn't this negative result appropriate?

-Tom

On Tue, May 10, 2011 at 2:54 PM, Noelia Ventura wrote:
Hi Sarika,

This does not function for our particular data set as we include a 3 conditions: A = auditory, B = visual and C = audiovisual. We are now examining the multimodal region. In this region there is no response for the unisensory conditions and therefore this leads to a null result in the conjunction you suggested.

Do you have a solution for this? Or anyone else?

Thanks,

Noelia

El 09/05/2011 11:58, sarika cherodath escribió:
Hi,

I am not sure whether this could work, but you can make a subtraction of L1 and L2 for each condition and then do a conjunction to create the required contrast.

On Mon, May 9, 2011 at 2:47 PM, Noelia Ventura wrote:
Hi all,

We would like to compare directly the results of two conjunction analyses.  These conjunctions show overlapping clusters. One conjunction shows a larger cluster then the other. We would like to examine whether the voxels that show up for one conjunction but not for the other differ significantly from each other.

In more detail, we have two tasks in the native (L1) and non-native language (L2).  Each task consists of 3 conditions, (A, B, C).  In the random effects we use a full factorial within subjects design and create a contrast : (  and we do this conjunction for L1 and L2.  We would like to know in which voxels the conjunction of L1 > L2.

However, in spm you cannot directly compare to conjunctions with each other. Or can you?

We would like to use imcalc to test where i1 = conj L1, i2 = conj L2 and our expression is i1 -i2> 0. However, i think we obtain a binary image from that but we need a statistical image. Can anyone provide a solution for this?

Noelia

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Sarika Cherodath
National Brain Research Centre
Manesar, Gurgaon -122050
India

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____________________________________________
Thomas Nichols, PhD
Principal Research Fellow, Head of Neuroimaging Statistics
Department of Statistics & Warwick Manufacturing Group
University of Warwick
Coventry  CV4 7AL
United Kingdom