Dear SPM experts,
I am relatively new in SPM and I have some questions for you about fMRI.
1): In SPM99 when I specific and estimate a model I always get the message: "gray -> beta not uniquely specified". I
insert in attachment a tipical example where I have: 60 scans, 3 cycles, 6 epochs, one condition of on and one
condition of rest, 10 scans for epochs.
If I set the following parameters I get the result showed in attachment:
- interscan interval: 3 sec
- scans per session: 60
- number of conditions: 1
- stochastic design: no
- SOA: fixed
- SOA(scans): 20
- time to 1st trial (scans): 10
- parametric modulation: none
- are these trials: epochs
- select type of response: fixed response (box-car)
- convolve with HRF: yes
- add temporal derivatives: no
- epoch length (scans): 10
- interactions among trials (Volterra): no
- user specified regressors: 0
- remove global effects: none
- high-pass filter: 120
- low-pass filter: HRF
- model intrinsic correlations: none
- setup trial- specific F- contrasts: no
I can't find why I have the message "beta not uniquely specified" that I have with different model too. Is this
message a error message or only a warning message?
2): What does mean "remove global effects" and when I must use these option?
(I see that, sometime, activations map is strong depending on the use of these option)
3): Does high-pass filter and low pass-filter modify sample data or only the model?
(I think the last one)
4): In "realign" what does mean "adjust sampling errors" and when I must use these option?
Thank you in advance for your help.
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