Dear SPM experts,
I have a problem regarding the inclusive mask. My conducted a masked priming lexical decision task, and the procedure started with a fixation, a mask, a prime, another mask and finally a target word (all within one TR). The prime could be a word which was visually similar/dissimilar to the target word. The position of the prime and the target could be a total blank. I defined a prime contrast (dissimilar minus similar) and a word contrast (target word present minus blank ). I looked for activated voxels of the priming effect within the constraint of the activation maps of the word contrast. So in the second level analysis, I used small volume correction on the prime contrast by entering the image of the word contrast. I expected that the activated voxel number under the prime contrast should decrease after I entered the word contrast in the small volume correction. However, the activated voxel number under the prime contrast actually increased after I entered the word contrast in the small volume correction. Could you please tell me why it was that?
What is the difference between using a mask and using the small volume correction? Finally, what is the difference between percent signal changes and beta value and how to output the percent signal changes over multiple voxels?
Thank you!
Sincerely,
Cath
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