This particular use of 3dLocalstat may not be what you expect. The stat parameter here essentially computes a voxel value based on the bin step. Consider this example:
3dLocalstat -prefix testperc.nii.gz -nbhd 'SPHERE(-5)' -stat 'perc:1:100:25' func_slim+tlrc.'[1]'
The stat format for the percentile uses "perc:start:stop:step" as its parameters all expressed in percent (not decimal fractions). This command computes the values at the 1%, 26%, 51% and 76%ile in a 5mm radius local neighborhood around each voxel. The output has 4 subbrick volumes. Switch among these with the Overlay panel control.
The median would be computed with either of these commands, and either would have only a single output subbrick volume (the start and stop are equal):
3dLocalstat -prefix testperc2.nii.gz -nbhd 'SPHERE(-5)' -stat 'perc:1:100:25' func_slim+tlrc.'[1]'
3dLocalstat -prefix test_median.nii.gz -nbhd 'SPHERE(-5)' -stat 'median' func_slim+tlrc.'[1]'
