In order to model this, there really must be a baseline condition. Otherwise there is no distinction between "equally active for all tasks" and "dead salmon" - we can only evaluate contrasts.
In your case, it is not really possible to get separate beta weights for all 3 conditions. One of them must be considered as a baseline, to which the others could be compared. The 3 possible basic contrasts (A-B, A-C, B-C) would then simplify (A-B, A, B), were condition C to taken as the baseline.
Does this seem reasonable?
- rick
