Hi Katelyn,
Time starts at t=0, and by the time of the linear regression, all voxels are assumed to be synchronized with the TR timing, as if the volumes were acquired at the beginning of each TR.
For example, assuming one run has only 3 time points, with TR=2s. Then the times for those volumes are t=0, t=2 and t=4, in seconds. While the "run" would last 6s, there would not be any data at time t=6, only up to t=4. So since the first volume is at t=0s, the last is at t=(N-1)*TR. Your last volume is at time t=344s.
To be precise, an event at time 344.285 does come after the acquisition of a few slices. And even for those slices the did occur after it, there will be no measurable BOLD impact to speak of (the ideal BOLD response takes about 2s to even start pulling away from 0). Really, there is little point in stimulating subjects at the very end of a run.
Anyway, that is why you are getting the warning, 344s is the time for the last volume.
Note that stimulus times can be shifted if needed, by 3dDeconvolve directly, or by afni_proc.py or timing_tool.py.
Does that seem reasonable?
- rick
Edited 1 time(s). Last edit at 06/17/2019 01:51PM by rick reynolds.
