z-score within participants before or after averaging conditions

#1
Hi,

I have a Group(2) x Condition(5) ANOVA design. Group is a between factor and Condition is within. I'm specifically interested in interaction effects (not overall group differences). I want to z-standardize the data within each participant to account for inter-individual differences (participants might vary a lot in general responsiveness - independent of condition).

My question is: For each participant, do I z-standardize the whole data set across all conditions first and then calculate averages for each condition (each condition has 10 trials) or (again for each participant) do I calculate averages for each condition first and then z-standardize across the 5 conditions? And does the order even matter?

Thanks a lot,

Catarina