For a two factor GLM analysis with two levels, I'm uncertain as to why the Freesurfer GLM measurement of the interaction effect of say, group and gender, is a t-test and not an F-test. In my case, my factors are group (healthies vs patients) and gender (male vs female). For a 2x2 two-way ANOVA analysis, the measurement of an interaction is always an F-test.

For example, on the following Freesurfer FSGD Wiki page (Four Groups (Two Factors/Two Levels), No Covariates)
http://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G0V
under Contrast 7, it claims the gender-x-handedness is a t-test.

Is this contrast a t-test or actually an F-test?

Thanks,
Chris