Hi - this is because of a change in the definition of what the model
formation does with "pre-zero" data. In older versions we effectively
padded the pre-zero volumes with zeroes, hence your 3.3.11 result. In
the latest versions we changed things so that the convolution
effectively ignores the concept of pre-zero data - hence there is no
rise time, as you see in your 4.1.0 result. In most situations this
gives more appropriate results.
If you wish to get FEAT to revert to what you saw in 3.3.11, which may
well be appropriate in your case, you can move the phase=25s from the
Shape-phase entry box to the Convolution-phase entry box instead,
which gives you what you want.
Cheers.
On 2 Dec 2008, at 17:28, Sebastian Rodrigo wrote:
> Dear FSL expert,
>
> a question about design model inside FEAT. Using Feat (FSL 3.3.11)
> for a
> block design starting with ON phase (full model setup, ON=25 sec
> OFF=25 sec
> and phase=25 sec) I get three nice HRF convolved blocks with an
> appropriate
> delay at the begining. Using FSL 4.1.0, I get a strange model, using
> the
> same parameters (design.fsf verified), the first block has a
> different shape
> than the others (see attached capture). How could you explain it ?
> Thanks a lot.
>
> Best regards
>
> Sebastian
> <FEAT_model.png>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
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