Step 5. Smooth functional images

This step smooths all normalized functional images produced at the previous stage. It will produce new swaV* files.

click on “SMOOTH”

For Images to Smooth, select all your normalized scans. session1/waV*; session2/waV* etc.

for FWHM enter 8 8 8

FWHM stands for Full-Width at Half-Maximum, and it defines the size of the Gaussian kernel used for smoothing (in this case, this will be a Gaussian function with 8 mm width, measured at the mid-point between the base of the function and its peak). Smoothing it performed to compensate for residual between-subject variability after normalization, and to permit application of Gaussian random field theory at the statistics inference stage.

The size of the kernel should be at least 2.5-3 times that of the voxel size. The kernel is said to be isotropic, if it has the same extent in all three dimensions. When a single value is entered, isotropic kernel with the same extent in all dimensions is created. If you want to specify a non-isotropic kernel (e.g., smoothing more in the through-plane direction), enter a 3-value vector at the “smoothing {FWHM in mm} prompt, e.g., [6 6 10].