Dear SPM,
I have 13 subjects with 54 fMRI scans/subject and every session has the
same structure:
6 scans for condition A,
6 scans for condition B,
6 scans for Rest, and so on for 3 times.
The sequence is [ Rest A B Rest A B Rest A B]
I did the first level analysis for every subject.
A vs Rest (-1 1 0 -1 1 0 -1 1 0)
B vs Rest (-1 0 1 -1 0 1 -1 0 1)
A vs B (0 1 -1 0 1 -1 0 1 -1 )
Then I did the next analysis as follows:
1. fmri models: specify and estimate a model.
2. mum of session: 13
3. select scan for session 1-13: the snr*.img of 13 subjects.
4. interscan interval (secs): 5 (TR=5000ms)
5. are conditions are replicated? Yes
6. are timing/parameters the same? Yes
7. number of conditions or trials: 3
8. name for condition/ trials 1-3: trial1.. trial2.. trial3..
9. SOA: fixed
10. SOA(scans) for trial1: 18
11. times to 1st trial(scans):0
12. SOA(scans) for trial2: 18
13. times to 1st trial(scans):6
14. SOA(scans) for trial3: 18
15. times to 1st trial(scans):12
16. parametric modulation: none
17. are these trials: epochs: fixed response (box-car)
18. convolve with hrf: yes
19. add temporal derivatives: no
20. epoch length for trial1-3: 6.. 6.. 6
21. interactions among trials (Volterra) no
22. user specified regressors: 0
23. remove global effect: scale
24. high-pass filter?: specify
25. low-pass filter: hrf
26. model intrinsic correlations?: none
27. setup trial-specific F-contrast?: yes
At RESULT, I set the contrast as these:
A vs Rest (-1 1 0 -1 1 0 -1 1 0 -1 1 0 -1 1 0 -1 1 0-1 1 0 -1 1 0 -1 1 0 -1
1 0 -1 1 0 -1 1 0 -1 1 0)
B vs Rest (-1 0 1 -1 0 1 -1 0 1 -1 0 1 -1 0 1 -1 0 1 -1 0 1 -1 0 1 -1 0 1 -
1 0 1 -1 0 1 -1 0 1 -1 0 1)
To see the (A vs Rest)vs(B vs Rest), I used exclusive masking for (A vs
Rest) with (B vs Rest).
Then, select
Correct height threshold: no (Does it mean I didn’t do the correction for
multiple comparisons?)
Threshold (T or p value): 0.001
Then I got a “fine” result.
In fact, I also tried to select
Correct height threshold: yes
Correct p value: 0.05
But the activations regions can’t be found.
I think i don't understand very well the thresholds and the p-values
(corrected, uncorrected)
And are there some mistakes in the above process?
Thank you very much.
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