When should I mean scale (aka mean norm) and/or linear detrend my data?
Both of these are options applied independently to each time series in each voxel from each tes file. The mean scale option divides each time series by its mean. The detrend option removes any linear trend from the time series. Both options are applied directly to the time series data at the time of the regression, so they are reflected in the regression results but they don’t modify your data files. (You could apply either operation as a preprocessing step, but we don’t currently make that option available in VoxBo.) Mean scaling can remove scaling artifacts, the sort you’d expect if signal values from the scanner were multiplied by a different constant in each run (magnifying signal and noise). It’s not the same as the effect removed by scan effect covariates, which can account for a different constant added to each run. Both are conceivable sources of unexplained variance, and it costs little to remove them when appropriate. Note that mean norming is pointless when you just have a s
