Dear SPM masters,
I am performing source reconstruction on the difference between two
ERPs using group inversion (20 subjects), standard reconstruction
parameters on a narrow temporal window (20 ms) on a well-known ERP
wave (N170). Standard MNI brain.
I have two questions:
1) Why do I have spurious reconstructions like the one attached
(source reconstruction on one subject, but this appears to be
relatively frequent in my analyses)? Is there a way to avoid such
artifacts?
2) A more general question. As far as I know, algorithms of
reconstruction of distributed sources use a noise covariance matrix
either on a baseline or on a separate set of data where no task
-related activation occurs. How does it work with SPM? Is this
computed implicitly somewhere or does it work differently? Since I am
computing a difference between ERPs, I expect results independent from
baseline correction. Am I right or does it influence the noise
covariance matrix? I could not find such information in the SPM
manual.
Thanks for your feedback,
Marco
--
Marco Buiatti, PhD
CEA/DSV/I2BM / NeuroSpin
INSERM U992 - Cognitive Neuroimaging Unit
Bāt 145 - Point Courrier 156
Gif sur Yvette F-91191 FRANCE
Ph: +33(0)169.08.65.21
Fax: +33(0)169.08.79.73
E-mail: [log in to unmask]
http://www.unicog.org/pm/pmwiki.php/Main/MarcoBuiatti
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