Jade -
Stimulus onset times need to be specified in units of volumes (=scans).
Thus if your first block started at time 5s, and your TR were 3s,
you would enter 1.67.
If you want to enter onset times for multiple blocks of multiple
conditions,
they need to be entered as a Matlab cell array. If you had five
conditions
for example, you would need to first define a variable ons=cell(1,5)
(type
"help cell" in Matlab to learn about cell arrays). After defining the
values for, EG ons{1}=[0 15 20] (first condition block onsets), ons{2}=
[5 10 25] (second condition block onsets), etc...., when you then press
"Variable SOA" in SPM99, you can type "ons" and it will fill out all
condition onsets automatically.
Rik
Ngoc Thai wrote:
>
> Hi SPM users,
>
> I have been trying to create a matlab file that contains vectors that will allow it to know my SOA for each epoch, however, I
> was assuming that I just need to calculate which slice the stimulus onset occurs, as I am assuming that scans = slice not volume is
> this correct?
>
> I had a look at Rik Henson's file ( from example dataset named sots)and his SOA matlab file says that values are in TR I have now idea what he means by this, I know that the TR = repetition time, in my case = 3sec.
>
> Could anyone who has made such a file like this to enter in the design matrix under variable SOA help? If so how do you go about calculating the values to enter, are they in time, slice or volume?
>
> My design is a 2x2 factorial block design with 2 tasks and 2 delays
> thus 2 control conditions with corresponding delays.
> all trails are randomised and blocked into 3 trials of the same condition.
> My TR = 3sec, 16 slices per volume total of 642 volumes per subject
> short delay trials = 10volume per epoch, long delay trials = 14volumes per epoch.
>
> Many thanks
> Jade
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DR R HENSON
Wellcome Department of Cognitive Neurology
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