Hi Cornelius,
Perhaps you could have a look at the contrast images (what contrast were you
looking at ? a simple positive effect ?)
If they are very different then the discrepancy will be in the
parameter estimation algorithms (btw. you did'nt mention anything about
correlated errors).
If they are similar the dicsrepancy will be in the classicial inference
machinery (eg. smoothness estimation) etc.
Best,
Will.
Cornelius Werner wrote:
> Hello list,
>
> just out of curiosity, I analyzed a fairly complex (and long) erfMRI
> experiment with a 3x3 factorial design with both SPM2 and FSL3.2b. I tried
> to keep everything as close to the other package as possible, i.e. I
> adjusted both smoothing kernels to 5mm, set the high pass filter to 128s,
> used gamma function + temp. derivative in FSL (standard delay) / canonical
> hrf + tdv in SPM2, entered identical onset vectors, specified identical
> contrasts and so on. I set the duration for my events to the actual 1.5
> seconds in both packages, as FSL doesn't allow 0-durations.
> Now one of the packages gave me "blobs" on a
> corrected-for-multiple-comparisons level of 0.05, where the other didn't
> show anything worth mentioning on a uncorrected p=0.001 level. Is that
> possible at all, given the similarity of the statistics? Has anyone
> experienced something similar? I am aware of the comparison done by
> Bianciardi et al (NeuroImage 2004), but differences were marginal at
> best...!
>
> Thanks for your help,
> Yours,
> Cornelius
>
> --
> Cornelius Werner
> Institut fuer Medizin (IME)
> AG Kognitive Neurologie
> Forschungszentrum Juelich
> 52425 Juelich
> Germany
>
> Tel. +49-(0)2461-61-8609
>
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
|