Dear SPMers,
I need some advice on timing parameters for an event-related design. Each of my trials lasts 10 seconds, with a 1-second video clip presented 4 s. after the start of the trial. I’m only interested in brain activation during the clip and how it varies across 4 conditions (4 types of video clips). I plan to present a fixation cross of varying durations between trials.
From what I understand, since I plan to contrast activation across conditions and I’m not interested in contrasting each condition with a baseline (null events), the duration of my fixation cross does not need to be very long, but only needs to shift the timing of my events so that they do not always start at the beginning of a TR. Is this right?
With a 3 sec TR, would it be ok for me to use a fixation cross with durations that vary randomly from 500ms to 2500ms in steps of 500ms?
Any advice would be very helpful, thanks!
Fanny
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