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Dear Sarb, > 1. The F-contrast (effects of interest) shows only few small significant > regions at p<0.05 (uncorrected). However, if I look at the contrast c1-c2 > (i.e. 1 0 -1 0 0 0), I get highly significant effects in those areas I > expected to see. How is it possible that I don't find these regions in the > F-map? (I think it is important to add that the contrast 0 0 -1 0 0 0 did > not show a significant effect either). I recently encountered similar problems in one of my analyses (sparse and insignificant effects when I looked at the F spanning the space of all covariates, yet significant effects when I examined a specific combination of those covariates). I think this can be explained by two factors: the difference between a t and a F contrast on the same data, and the loss of degrees of freedom when you use an F contrast with n different covariates. In a comparison between a t and an F, you need to double the p value of your F to ensure a similar level of significance: so if your t contrast has a p of <0.001, your F should be <0.002 ( this is because a t is a one-tailed test, while the F is two-tailed). The loss of degrees of freedom results from your F examining the variance explained by an n-dimensional space spanned by your covariates. The t looks at the variance explained by the one-dimension spanned by your contrast: so, due to this constraint on your anlaysis, the significance of your effects increases. If you want to ensure that your F and t are comparable, construct an F which has similar degrees of freedom to your t, and adjust your significance levels at which you display it accordingly (ta to Jesper A. for tidying up the preceeding explanation!). > 2. If I want to plot the adjusted data of the areas showing significant > c1-c2 difference, it appears that this is not possible. I get the message > "no raw data has been saved at this location". I assume that this has to do > with the fact that there is no significant F-contrast at the same location, > and therefore no raw data has been saved there. Is there a way to plot these > data? As far as I'm aware, the timeseries data for these voxels is not retained, so all you can look at is the parameter estimates. I think you need to repeat your estimation, but change the F contrast threshold in the spm_defaults menu (it's in the 'defaults' button, under 'spm statistics'.) If you make this more lenient, your voxels should survive the cruel scythe of the F cut-off. Best Dave