I think Anthony is correct here, users should subtract ~TR/2 from the stimulus times (actually (N-1)/N * TR/2 s, assuming N slices are evenly distributed over the TR), but TR/2 is close enough if there are many slices. Adding it would double the problem people might be experiencing mixing these packages.

Suppose TR=2s and the first event is at time t=1s. The offset of that event from the beginning of the run and from the beginning of the initial volume is 1s. But if the slices are shifted so it is as if they were acquired also at time t=1s (approximately), then the offset for that first event should be t=0, since it would correspond to the time of that initial volume. Notably, an event originally at time t=0 would now occur "before" the first volume. Complications...

If tshift were used to make it as if the volumes were acquired later, then the events would seem to occur earlier, relative to the timing of the data.

- rick



Edited 1 time(s). Last edit at 09/23/2021 05:06PM by rick reynolds.