> I take it from your answer that the ANOVA won't work for unequal sample sizes in each group (11 13).
You can run 3dANOVA3 -type 5 because of unequal number of subjects across group.
> main effect of group for each condition
This is a two-sample t-test, and you can write up a script for color condition like
3dttest -prefix ... \
-set1 ColorSubj1inGroup1 ColorSubj2inGroup1 ... \ # 11 subjects
-set2 ColorSubj1inGroup2 ColorSubj2inGroup2 ... # 13 subjects
and do the same for Achromatic condition.
> main effect for each condition
Do you mean the effect of Color condition for all 24 subjects? And the same for Achromatic condition? If so, you need two one-sample t-test:
3dttest -prefix ... \
-base1 0 \
-set2 ColorSubj1 ColorSubj2 ... \ # 24 subjects
3dttest -prefix ... \
-base1 0 \
-set2 AchromaticSubj1 AchromaticSubj2 ... \ # 24 subjects
> any group x condition interactions
Get Color-Achromatic for each subject, then run a two-sample t-test:
3dttest -prefix ... \
-set1 (Color-Achromatic)Subj1inGroup1 (Color-Achromatic)Subj2inGroup1 ... \ # 11 subjects
-set2 (Color-Achromatic)Subj1inGroup2 (Color-Achromatic)Subj2inGroup2 ... # 13 subjects
HTH,
Gang