the percent checkbox - what is it for?

Mostly out of curiosity - near the autoRange option there is a checkbox with a percent (%) sign next to it. When I check the box, I see more activated voxels surrounding the clusters. What does that do? What is that for? I couldn’t find an explanation in any online documentation.

The title of this thread reminds me of an Edwin Starr song from the 60s. Nice.

Back to the question at hand:

Preliminary note, if you hover over a symbol/menu label in the GUI, then you see a brief help blurb. If you first click the “BHelp” button located in the lower left of the GUI (which stands for “Button Help”), and then click on the symbol/menu label you want, you will see a larger help description. That help description is in fact a button, so you can click on it when you are done reading it to make it go away.

In this case, the button help desc is:

This button determines whether the slider sets
the threshold based on percentile, rather than
value. At 0.75, you threshold away the bottom 75%
of the voxels that would be displayed with no
thresholding at all. At 0.5 you see the top half.
The slider power is ignored in percentile
mode, so 0.5 is the same as 5, 50, etc.
Zero voxels are not considered. Only positive
voxels are considered if 'Pos?' is set; otherwise,
the cumulative distribution percentages come from
the absolute value of the voxel values.

Before you click the “%” button, as you raise/lower the slider, the thresholding is applied directly at that number. So, if you move it up to 5, then the GUI applies that cutoff directly in the threshold volume, determining which voxels are seen (those >5) and those that aren’t.

After you click the “%” button, as you raise/lower the slider, that number is interpreted as a percentile for selecting a value within the cumulative distribution of threshold volume voxels, and the the thresholding is applied that that percentile value within the cumulative distribution. So, now if you put the threshold slider at 5, you will threshold out the lowest 5% of voxels in the threshold display.

For thresholding a stats dsets, you will see that the p-value below the threshold changes as you toggle percentile on/off, because it is translating a different value in either case: either the direct slider value (when “%” is OFF), or the value in the cumulative distribution at that slider percentile (when “%” is ON).



The “%” indicates a percentile distribution of non-zero voxels within the threshold sub-brick. The range on the threshold slider will always go between 0 and nearly 100 percent. Depending on the power-of-10 range, 5 could threshold at 50%, 5%, 0.5%,0.05% percentiles. Halfway up any threshold slider will be around 50%.