Thanks a lot for quick answer, Eugene.
On Tuesday 17 November 2009 15:13:00 Eugene Duff wrote:
> Hi Martin:
>
> My opinions:
> > My concerns are:
> > 1. should I actually bother with randomization of the ISI, since the
> > event duration 1) + 2) + 3) could be enough to obtain un-convoluted HRF,
> > and reaction time could also be random.
>
> You may as well, just to be safe, in case some subjects always take the
> maximum 5 seconds of time.
Thanks for pointing this out! I didn't consider this scenario.
>
> > 2. In the higher-level group analysis, the differences in event order and
> > different event timing for each subject are not an issue since
> > first-level variances are carried up from the first-level analysis, but I
> > presume that I
> > should use cope images and not feat directories, because the model will
> > be different for each subject.
>
> The differences in event order and timing should not be an issue. You can
> still use Feat directories as you will still have the same number and
> order of evs/copes in each lower analysis.
>
Here I have a misunderstanding. The number of EVs will indeed be the same, but
if I shuffle the order of events belonging to each contrast, the HRF/model for
each contrast will look different for each subject.
The documentation on higher-level analysis (
http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html ) says:
"You can choose whether your higher-level design matrix will be applied to a
set of lower-level cope images or a set of lower-level FEAT directories. In
the latter, more normal, case, each contrast in the lower-level FEAT
directories will have the higher-level model applied..."
which doesn't seem to be my case, if I undersdand things correctly?
Thanks,
Martin
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