BLOCK output longer than expected from 3dDeconvolve

AFNI Message Board
1

Hello,

I’ve been looking at the ideal functions resulting from 3dDeconolve, and was quite puzzled at the length of each trial.

Here is an example:

3dDeconvolve -nodata 195 2.0 -num_stimts 1 -polort 3 -x1D example-X.xmat.1D
-stim_times 1 ‘1D:112 168 322’ ‘BLOCK(14)’

Now, the TR here is 2. Since the X.xmat.1D files are in TR’s, I expected to see a convolved response function with length of 8 to maybe 9 TR’s. But in my X.xmat.1D file, I noticed the 1st trial is roughly 15 TR’s long. Equating to about 30 seconds. Practically double the stimulus duration.

What is the case?

Any help would greatly be appreciated.

Thanks.

Michael

2

Hi Michael,

The BOLD response to an instantaneous event is expected to
last between 12 and 15 seconds, depending on how one chooses
to model it. The BLOCK function is a longer one, lasting closer
to 15. And that means a 29 s response to a 14 s stimulus, which
lasts 14-15 TRs.

  • rick
3

Thank you Rick for your explanation.

Michael