Gotcha!
Gang,
One more point for one of the covariates. The covariate called Accuracy is actually a binary number when considering the trial data: 1 = correct and 0 = incorrect. In that case, would you proceed the same way to subtract the group mean for each condition of interest (i.e. Time1, Time2, Time3, and Time4)? For example, if the average accuracy for Time 1 across all participants is 88.7% correct, then would I subtract 88.7 from a 1 or a 0, depending whether the trial was correct or incorrect, respectively. Something seems weird about this approach with a binary variable.
Best,
Christine