Where can I find a scroll bar that allows me to change the threshold value on an image? I do not think I am using the one found under the "define function" window extension correctly.

You may need to set the Thr sub-brick on the Define Function control panel to be the correct one. The slider on this panel applies the threshold to that sub-brick -- only voxels whose values are greater-than-or-equal-to the slider value will get colored. (The colors are determined by the values in the Func sub-brick and the color "pbar".) If you need to set the threshold to a value larger than 0.9999 -- for example, if the Thr sub-brick is a t- or F-statistic -- then you can set the scale factor for this slider using the ** control just underneath the slider -- for example, setting ** to 2 changes the range of the slider to be from 0-99.99.

This is the only tool in the AFNI GUI for interactively setting the threshold used for colorization in an image window.

bob cox