Hello AFNI experts,
I want to double check that I am using the new option of AFNI Clustsim correctly. I have in the past used the version that uses the FWHM and I am surprised by how much different the cluster sizes when using the ACF option.
For example: NN3 2 sided, at pthr 0.05 and alpha 0.05, the original version cluster size is 768 voxels, whereas in ACF version it is 3590. This is a 4 fold increase in voxels needed for a cluster to survive correction. Is this in accordance with what is expected with the ACF option?
I am running cluster correction for a 3dMVM model with both within subject (3 conditions) and between subject regressors. Here is my code for calculating smoothness and running clustim with the ACF option. I should note that my single-subject data was processed in FSL, so the res4d.nii file for single subject data should be equivalent to errts file generated by afni_proc.py.
foreach n (…)
foreach cope(1 2 3)
3dFWHMx -dset res4d.nii.gz -automask -detrend -acf >> smooth_acf.1D
cat smooth_acf.1D >> /Volumes/danl/afni_clustsim/clusterize_step1_output_smoothness_residuals_acf.1D
3dClustSim -mask mask.nii -acf 0.55 5.44 18.0 -LOTS -iter 10000 -nodec -NN 123 -prefix 3dClustsim_ACF_3dMVM_GroupxAgexEmotion