I would say one has to think about SSSt as a temporal filtering method -
and you don't correct your leadfield after low-pass filtering either, for
example. But this raises another interesting question: If SSS (with or
without ST) only removes activity from sources outside the sensor array,
it should only remove patterns that are in the null space of the leadfield
- i.e. no correction would be required. If it removes patterns that are
NOT in the null space of the leadfield, these sources could potentially be
generated inside the head (where the brain is) - i.e. it might remove
signal! I would hope that it's the former.
Olaf
> Burkhard -
>
> I thought so too, but another colleague thought this was not the case.
> So if the Neuromag experts don't give the definite answer, we could have
> a vote?
>
> ;-)
> Rik
>
> Burkhard Maess wrote:
>> Hi Rik,
>>
>> this is an interesting question - but I think the temporal projection
>> does not modify the spatially organized leadfield. SSSt takes out the
>> part of the data which correllates highly between both expansions, but
>> you can not describe it by a certain spatial pattern as in the case of
>> the SSP.
>>
>> Cheers,
>> Burkhard
>>
>>
>> Rik Henson wrote:
>>> Dear Neuromeg -
>>>
>>> Could you let me know how I can correct my leadfields for prior SSSt?
>>> In other words, I have a leadfield matrix, L, of n sensors x p
>>> sources, and would like to extract some form of projection matrix
>>> from Maxfilter that I can apply to L in order to remove those
>>> components of the sensor data that have been removed by SSSt.
>>>
>>> Many thanks
>>> Rik
>>>
>>
>
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>
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> Dr Richard Henson
> MRC Cognition & Brain Sciences Unit
> 15 Chaucer Road
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> CB2 7EF, UK
>
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