John,
I would lean towards 4 sessions of 6 minutes. I've run subjects on 14 sessions of 4 minutes and 5 sessions of 10 minutes and I typically have more motion problems with the first variant (a greater amount of motion in later sessions and more opportunity for between session motion, as you mentioned). And based on when I've been in the scanner, a few longer sessions feels shorter than many short sessions because it's easier for me to keep track of how many sessions have gone by than by counting the minutes a session takes.
Hope this helps,
Nicole
-----Original Message-----
From: SPM (Statistical Parametric Mapping) on behalf of John Gelburg
Sent: Fri 7/31/2009 5:10 PM
To: [log in to unmask]
Subject: [SPM] What is recommended fMRI session duration?
Dear all,
I have a block design with 6 types of blocks and 20 sec block duration
and 6 sec between block fixation. I need 8 repetitions of each block.
So, I can have 8 sessions of ~3 min or 4 sessions of ~6 min. What is
preferable? Afterwards, there are some other sessions, but I would
like to focus on described sessions only.
Bellow are pros and cons I can think about:
Pros (to make 8 sessions):
1. shorter session = easier to preserve subjects attention for the whole session
Cons (to make 8 sessions)
1. The total number of sessions is larger, which may create an
impression for subject that the experiment is longer (to feel more
tired etc).
2. Is scanner signal variability between sessions is larger than within session?
3. More breaks between sessions may result in more subject movements.
Thanks for help,
John
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