Stim_times AM1 or AM2?

AFNI Message Board
1

Hi there,

Regressor files are organized in the following format in seconds: ONSET: DURATION. The duration of the events in each regressor should be the same, though sometimes there are very slight variations in the duration times (milliseconds) due to computer processing variations, so I wanted to specify the duration times in the regressor to model the events as accurately as possible.

For my afni proc script, I specified the regress_basis to be dmBLOCK, though I am not quite sure whether the stim_times should be AM1 or AM2 or whether I need to specify a specific stim_times. I read through the “AMRegression” information online but I am still not sure which option is appropriate.

I appreciate any help or suggestions you can offer.

Thank you,
Tamara

2

Normally use -stim_times_AM1 because you want to create a regressor that is adaptive to the varying duration across trials. I personally prefer adopting ‘dmUBLOCK(-X)’ instead of ‘dmBLOCK’ so that, to disambiguate potential confusions, the regression coefficient is explicitly associated with a specific duration X.