Hi
My experiment is to measure response to different types of music and visual stimuli. The subjects are given no task but have to freely listen or view a clip.
For the music test: I have music in which the tempo changes abruptly. But each tempo is played for at least 80 seconds. I tried many designs as given below:
1) Tempo1 : Onset 1 50
duration 30
Tempo2: onset 75 125
duration 30
t-contrasts: 1 -1 (tempo1 - tempo2) and -1 1 (tempo2 - tempo1)
2) Tempo1 : Onset 1
duration 60
tempo1a : onset 10
duration 20
tempo1b: onset 30
duration 20
(similarly for tempo 2. This was to take care of any saturation because of the long durations).
Contrast (gets very confusing here) : 0 1 -1 (for set of conditions covering tempo1 duration) and 0 1 -1 (for the tempo2)
Of course, there are many combinations here, but the idea is to remove any saturation effects while comparing tempo1 response to tempo2.
Question 1: Am i doing something wrong or is the design OK?
As suggested by you, I also did ICA (GIFT) and have the temporal & spatial map for each subject.
Question 2: Can I compare the region of interest as seen in the GLM/SPM to that obtained from ICA? I see that people have looked at it independently.
I really appreciate all help, as confusion has set in as I do more & more analysis.
regards
Kavita
----- Donald MCLAREN <[log in to unmask]> wrote:
> What are you trying to detect?
>
> When you set up your design, it creates an expected hemodynamic response. It
> then tries to fit that to your data.
>
> Your blocks need to relate to something in the task and not be random. If
> you truely have a random pattern that you have no expectation when the brain
> comes on and turns off, then you should be using ICA.
>
> Best Regards, Donald McLaren
> =================
> D.G. McLaren, Ph.D.
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Research Fellow, Department of Neurology, Massachusetts General Hospital and
> Harvard Medical School
> Office: (773) 406-2464
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> On Wed, May 18, 2011 at 11:00 AM, Kavita Vemuri <[log in to unmask]> wrote:
>
> > Hi
> > My experiment has no explicit task(well, that is an oxymoron!) - requires
> > free viewing of moving images. The fMRI collected is collected TR of 2
> > seconds and the total duration of the experiment is around 8 minutes . At
> > the 1st level analysis phase, I notice big variations when 'Onset'(block) is
> > changed from 20 to 22 with a duration of 20, for example. The design is in
> > seconds. Is this expected? For example: At an onset = 20 & duration = 20, I
> > see not even one voxel highlighted but when the onset=22 and the duration=
> > 22 or 25, there is huge response.
> >
> > Question: in an task independent/free viewing paradigm, can blocks be
> > selected in the design?
> >
> > Regards
> > Kavita
> >
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