Dear Alfonso, 

To investigate interaction effects in a 2 (case/control) by 2 (female/male) level design, am I correct in thinking that if I select my subject effects 'case', 'control', 'female', 'male' (each with a vector indicating 1 for yes, and 0 for no), entering [1 -1 -1 1] as the between-subject contrast will yield the interaction effect for (case > control) x (male > female)?

Further, to include further covariates like age or IQ, selecting one or more of those from the between-subjects factors, what does the contrast need to look like?

e.g. selected: age, IQ, case, control, female, male
what would I need to assess the effect of age on the interaction: [? ? 1 -1 -1 1]
what would I need to assess the effect of age and another covariate on the interaction?: [? ? 1 -1 -1 1]

Thank you very much for your help, 
Best wishes,

Charlotte