I'm planning an event-related fMRI-experiment to investigate the difference in processing natural and computer-generated facial emotion expressions.
I've seen a lot of studies that synchronize the scan acquisition with stimulus presentation. Is synchronization between the scanner and the stimulus presentation necessary for every trial or is it enough if the scanner and the presentation are synchronized for the first trial?
This question is asked assuming that trials are jittered.
I have a Matlab script to present my stimuli and I've decided on the acquisition parameters (see below). I'll have to start the stimulus presentation with Matlab over a button press after a few dummy scans, as the scanner is not equipped with a synchronization box that tracks the scanner pulses and conveys them to my stimulus delivery computer. So, my presentation is only synchronized with the first scanner impulse.
The stimuli will be presented according to the following parameters and in the following order:
- Fixation cross for 600-800ms (length randomly varying in 25 ms steps)
- Video for 3 seconds (length not varied, but video type (natural or computer-generated) is randomized)
- Blank screen for 3-5 seconds (length randomly varying in 250 ms steps)
- TR = 1.7s, TE = 30ms
- Whole brain acquisition
- Voxel size 3x3 mm, slice thickness = 3.9mm