Dear SPMers,
I’m planning to compare 2 groups (healthy vs. patients) using simple blocked-design fMRI task with 3 emotional valence conditions (NEGative/POSitive/NEUtral) & a TRAuma-related condition. NEU is basically a baseline condition, based on previous studies I expect: no between group differences on NEU, small differences on POS & NEG, large differences on TRA.
Assuming that TRA increases negative feelings in patients stronger & that this feeling will not abruptly decrease to baseline at the end of a TRA block I want to spilt the paradigm. That is:
(1) VALPARA: blocks of NEG/POS/NEU, each 6 blocks with 4 pictures, order of blocks randomized
>> After each blocks subjects rate their arousal on a visual scale using buttons
(2) TRAPARA: blocks of TRA/NEU, each 6 blocks with 4 pictures, order of blocks randomized
>> After each blocks subjects rate their trauma-strenghts on a visual scale using buttons
- Different but matched sets of NEU are used during VALPARA & TRAPARA
Using two paradigms I assume that processing of NEG/POS/NEU during VALPRA is not confounded by TRA-induced ongoing negative feelings.
In addition to our main contrast (patients vs. controls) I want to specifically test whether NEU in the TRAPARA are confounded by ongoing negative feelings induced by TRA. To this end I want to directly compare the NEU from the VALPAR to the NEU from the TRAPARA on the first level. If this comparison reveals within-subject differences in NEU between paradigms I assume a first-level comparison of ‘TRA vs. NEU from VALPARA’ will give me a more sensitive measure of TRA-related processing because these NEU are not confounded by TRA-induced activity.
My questions:
(1) Is it valid to compare conditions across the paradigms (e.g. NEU) on the 1-st level? Are there methodological/technical issues arguing against the comparison?
(2) Could the different ratings after each block (arousal/trauma) between the paradigms cause problems? Arousal & trauma will be related but not identical
(3) Would you recommend to acquire both paradigms within one session or two sessions (basically stop & re-start the scanner)?
Thanks very much; excuse the long text – I wanted to make it as clear as possible & best
Ben
