Hi,

I'm a newbie for AFNI 3dClustSim and I wonder if I can ask this question here. I use the command below to calculate cluster threshold in 3dClustSim:

3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05

where mask.hdr is the product during a group analysis in SPM8, and fwhmxyz is the average fwhm value from each subject's first-level model. As listed in the end of the post and summarized below, there are 9 outputs from the simulation:

output NN Thresholding Cluster size threshold in voxels
(1) 1 1-sided 122.8
(2) 2 1-sided 126.0
(3) 3 1-sided 126.3
(4) 1 2-sided 97.1
(5) 2 2-sided 98
(6) 3 2-sided 98.2
(7) 1 bi-sided 97.1
(8) 2 bi-sided 98
(9) 3 bi-sided 98.2

So which threshold should I use in my fMRI data?? And what's the difference between the 9 ones? I notice that results from 2-sided and bi-sided thresholding are the same.

Thanks.
Mike

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 1-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 1 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 122.8

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 1-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 2 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 126.0

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 1-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 3 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 126.3

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 2-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 1 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 97.1

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 2-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 2 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 98.0

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# 2-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 3 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 98.2

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# bi-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 1 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 97.1

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# bi-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 2 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 98.0

# 3dClustSim -mask mask.hdr -fwhmxyz 7.022 7.091 7.03 -iter 10000 -pthr 0.005 -athr 0.05
# bi-sided thresholding
# Grid: 79x95x69 2.00x2.00x2.00 mm^3 (190277 voxels in mask)
#
# CLUSTER SIZE THRESHOLD(pthr,alpha) in Voxels
# -NN 3 | alpha = Prob(Cluster >= given size)
# pthr | .05000
# ------ | ------
0.005000 98.2