The dialog window will indicate Underlay or Overlay
coresponding to which button you clicked.
The chooser will list the datasets available in the current directory.
By default when you start afni, it will automatically load the
first dataset alphabetically and that will be selected in your chooser
menu. (You can set the AFNI_START_SMALL environment variable to
YES which will default to loading the dataset with the smallest
file size first for speed)
The left column has prefix names of datasets.
Datasets without an extension are in afni’s .BRIK and
.HEAD format.
NIFTI formatted dataset will show the .nii or .nii.gz
extension.
The right column has a little information about each dataset.
How dataset was classified when it was created. Usually from
to3d, dcm2nii_afni, dimon, etc..
Number of sub-bricks.
The * indicates that the dataset can be graphed
(see here).
The z at the end indicates that the dataset is compressed.
In this example:
FT_anat is an anatomical bucket dataset with 1 sub-brick
and is in uncompressed afni format.
The next 3 datasets are eco-planar (EPI) datasets with 152
sub-bricks (TRs) in uncompressed afni format.
The next 2 datasets are eco-planar (EPI) datasets with 152
sub-bricks (TRs) in NIFTI format. One uncompressed the other
compressed.