>You can specify any mask you like in the Post-stats section of the FEAT
>GUI, under prethreshold masking. This adjusts your multiple comparison
>threshold correction appropriately.
Just wanted to add my $0.02 here:
It may be worth noting that the key word here is "appropriately." Because
the multiple comparisons are based on the number of resels and resels in
turn depend on the smoothness of the GRF, the volume of space, and the
surface area of the space, any convoluted mask (such as a GM mask) is
likely to have a very large surface area and hence a *larger* number of
resels than without the mask.
Of course, there are other reasons why using a GM mask might be a good idea
(like restricting activations to GM).
Cheers,
Joe
Joseph Devlin, Ph. D.
FMRIB, Dept. of Clinical Neurology
University of Oxford
John Radcliffe Hospital
Headley Way, Headington
Oxford OX3 9DU, U.K.
Phone: +44 (0)1865 222 738
Fax: +44 (0)1865 222 717
Email: [log in to unmask]
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