Thanks!!

So, I tried what you suggested plus adding the -acf command . But did not work (see below)
I have a total of 35 sub-bricks (see image attached)

3dFWHMx -dset mema++.6_E-S_resZ+tlrc'[0:34:(2)]' -acf -out E-S_FWHMx
++ 3dFWHMx: AFNI version=AFNI_17.0.09 (Feb 10 2017) [64-bit]
++ Authored by: The Bob
** ERROR: selector syntax error 5 ':(2)]'
** ERROR: bad sub-brick selector [0:34:(2)]
** FATAL ERROR: Can't open dataset 'mema++.6_E-S_resZ+tlrc[0:34:(2)]'
** Program compile date = Feb 10 2017


However, I try this (see below) and it worked:

3dFWHMx -dset mema++.6_E-S_resZ+tlrc'[0..$(2)]' -acf -out E-S_FWHMx
++ 3dFWHMx: AFNI version=AFNI_17.0.09 (Feb 10 2017) [64-bit]
++ Authored by: The Bob
*+ WARNING: removed 131033 voxels from mask because they are constant in time
++ start FWHM calculations
+ FWHM done (0.00 CPU s thus far)
++ start ACF calculations out to radius = 12.25 mm
+ ACF done (0.00 CPU s thus far)
3.88083 3.95934 4.43569 4.08479
0.747622 2.32492 9.72146 6.10881
++ ACF 1D file [radius ACF mixed_model gaussian_NEWmodel] written to 3dFWHMx.1D
++ 1dplot: AFNI version=AFNI_17.0.09 (Feb 10 2017) [64-bit]
++ Authored by: RWC et al.
pnmtopng: 42 colors found
+ and 1dplot-ed to file 3dFWHMx.1D.png

So, my questions are:
-Why is not working when I write: 3dFWHMx -dset mema++.6_E-S_resZ+tlrc'[0:34:(2)]' -acf -out E-S_FWHMx
Am I choosing the wrong sub-bricks number? (see image below)

-is this command ok? 3dFWHMx -dset mema++.6_E-S_resZ+tlrc'[0..$(2)]' -acf -out E-S_FWHMx
I mean, writing [0..$(2)] instead of '[0:34:(2)]

-If the command above is ok, the output is a file called: 3dFWHMx.1D
I assume the values in this file are the acf values. Which ones do I need to use for 3dClustSim?
The table looks like:
0 1 1 1
2 0.721748 0.721851 0.742904
2.82843 0.541156 0.545359 0.551906
3.4641 0.417775 0.423102 0.410013
4 0.34554 0.337426 0.3046
4.47214 0.279764 0.276865 0.226289
4.89898 0.233509 0.233667 0.168111
5.65685 0.178671 0.179776 0.0927813
6 0.162576 0.162904 0.0689275
6.32456 0.15554 0.150159 0.0512065
6.63325 0.14018 0.140327 0.0380415
6.9282 0.12457 0.132567 0.0282612
7.2111 0.129147 0.126291 0.0209953
7.48331 0.118861 0.121088 0.0155975
8 0.11475 0.112838 0.00860836
8.24621 0.109159 0.109446 0.00639519
8.48528 0.111247 0.106392 0.00475101
8.7178 0.0983605 0.103604 0.00352954
8.94427 0.101126 0.101029 0.00262211
9.16515 0.0982441 0.0986284 0.00194797
9.38083 0.0904522 0.0963737 0.00144716
9.79796 0.091374 0.0922211 0.000798694
10 0.0875434 0.0902942 0.000593353
10.198 0.0892459 0.0884527 0.000440804
10.3923 0.0866942 0.0866883 0.000327475
10.7703 0.082545 0.0833654 0.000180736
10.9545 0.0827532 0.0817966 0.000134269
11.3137 0.0766195 0.0788235 7.41039e-05
11.4891 0.0783004 0.0774124 5.50521e-05
11.6619 0.0762587 0.0760476 4.08984e-05
11.8322 0.0766266 0.0747266 3.03835e-05
12 0.0749448 0.073447 2.25721e-05
12.1655 0.0792722 0.0722067 1.67688e-05


many many thanks!