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November 27, 2002 03:43PM
Since FMRI can only detect differences, unless you have some rest (or other null task) periods in your experiment, you can only detect activation differences between your tasks (e.g., B-A, C-A, and D-A), rather than activation magnitudes.

However, assuming you have made separate activation maps for each task, your problem is now how to combine them into a single map that shows something useful. I suppose one useful thing would be an indication of which task(s) activated which voxels. To do this fully, you need 15 colors to indicate the various possible combinations (A only, A and B, A and C, ... , A and B and C and D). The main problem with this is that it is hard to come up with 15 distinct colors. If you do have 15 colors, then you could make a fim dataset with each voxel being binary-encoded for the presence or absence of A,B,C,D response, using 3dcalc. Then each voxel would have a value from 0 (no activation) up to 15 (activation from all tasks). Then you could display this in AFNI with the number of overlay colors set to 15.

bob cox
Subject Author Posted

Analysis on multiple task design

Xiangchuan Chen November 27, 2002 03:25PM

Re: Analysis on multiple task design

bob cox November 27, 2002 03:43PM

Re: Analysis on multiple task design

xxj November 28, 2002 11:50AM



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