Alexander/Eric -
If it's any help, I can report that for a group fMRI analysis
on 17 subjects comparing faces vs houses (ie a
well-characterised contrast), the results in SPM5 were much
better when determining normalisation parameters via John's
"unified segmentation", rather than via the more "traditional"
approach (i.e, the "normalise" button, as in SPM2).
Having said this, the initial affine part of SPM5's
segmentation sometimes failed on our structurals, unless they
were manually re-positioned, possibly because of attenuation
bias or excessive neck (to overcome this automatically, I
adopted a two-pass segmentation approach, which seems to work
on ~30 subjects so far).
Presumably for the same reason, some of the normalisation
parameters determined via the more traditional normalisation
were clearly wrong, and I must admit that I didn't play around
with the regularisation, which might have given better results.
Rik
--------------------------------------------------------
DR RICHARD HENSON
MRC Cognition & Brain Sciences Unit
15 Chaucer Road, Cambridge,
CB2 2EF England
EMAIL: [log in to unmask]
URL: http://www.mrc-cbu.cam.ac.uk/~rik.henson
TEL +44 (0)1223 355 294 x522
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MOB +44 (0)794 1377 345
--------------------------------------------------------
>>-----Original Message-----
>>From: SPM (Statistical Parametric Mapping)
>>[mailto:[log in to unmask]] On Behalf Of Hammers, Alexander
>>Sent: 30 March 2006 11:44
>>To: [log in to unmask]
>>Subject: Re: [SPM] SPM5 spatial normalization
>>
>>
>>Dear Eric,
>>
>>
>>It's kind of you to thank me even though I seem to have rather
>>added to your woes ;-)!
>>
>>I haven't really looked at the data with a comparison of the
>>various SPMs in mind, and I think one would have to think
>>pretty hard about how to do that - detection rate / yield?
>>Extent of abnormalities? Overlap of abnormalities with some
>>predefined idea of where they should be? Effect sizes? False
>>positives or lack thereof?
>>
>>Maybe someone has tackled this with simulations? It sounds
>>like the kind of thing Matthew Brett would do ;-)?
>>
>>As for your reviewer, ok, you may be losing some sensitivity
>>but if you're involved in ongoing / long-term studies you
>>might actually have had a reason to have stuck to somewhat
>>dated software - and the improvements I've seen are moderate
>>not revolutionary (say 1/15 individuals more in terms of
>>detection rate) so while it's certainly reasonable to
>>acknowledge the possibility of reduced sensitivity it seems a
>>bit harsh to me to trash a study for it (if that's what's happened)...
>>
>>Good luck, A
>>
>>-----Original Message-----
>>From: SPM (Statistical Parametric Mapping)
>>[mailto:[log in to unmask]]On
>>Behalf Of Eric Zarahn
>>Sent: 30 March 2006 10:53
>>To: [log in to unmask]
>>Subject: Re: [SPM] SPM5 spatial normalization
>>
>>
>>Dear Alexander,
>>
>>Thanks very much for your answer. I was mainly asking because a
>>reviewer claimed that by using SPM99 instead of SPM5 one is
>>reducing the sensitivity of group analyses of functional imaging
>>data. I could certainly imagine this being possible, but I wished
>>to know if there was any empirical evidence of this. Again, thanks
>>very much for providing that empirical substantiation.
>>
>>Best,
>>Eric
>>
>>Quoting "Hammers, Alexander" <[log in to unmask]>:
>>
>>> Dear Eric,
>>>
>>>
>>> 99 vs 2: yes, for ligand PET (single scans per subject, i.e.
>>> conceptually the same as an fMRI second level analysis). The
>>> second (SPM2) study is submitted - if you can wait a little I can
>>> hopefully let you have a reference.
>>>
>>> 5 vs rest: Impressionistically, it's again an improvement (we
>>> didn't expect otherwise ;-) ) - we don't have hard data yet but
>>> we have test case datasets (real data with histological
>>> correlates) which could be used to directly compare if you're
>>> very keen to have hard evidence or back up the impression with
>>> some numbers.
>>>
>>> All the best,
>>>
>>> Alexander
>>>
>>> -----Original Message-----
>>> From: SPM (Statistical Parametric Mapping)
>>> [mailto:[log in to unmask]]On
>>> Behalf Of Eric Zarahn
>>> Sent: 30 March 2006 03:13
>>> To: [log in to unmask]
>>> Subject: [SPM] SPM5 spatial normalization
>>>
>>>
>>> Dear John and Group,
>>>
>>> Does anyone have any empirical evidence, published or otherwise,
>>> that
>>> spatial normalization in SPM5 or SPM2 leads to better sensitivity
>>> in
>>> second-level analyses than in SPM99?
>>>
>>> Thanks,
>>> Eric
>>>
>>
>
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