[FieldTrip] artifact rejection

["Jörn M. Horschig"]

Dear Qi,

Though I am not sure to what z-score formula you are referring to, I 
guess you are talking about the 'summary' mode of ft_rejectvisual. 
Z-scores are computed in different ways here, once across channels and 
once across time, leading to two different plots. The third plot is an 
accumulated plot of these two, where colors indicate the strength of the 
selected measure (e.g. z-score). Thus, in terms of the z-score formula, 
it is once computed with the average and standard deviation across the 
time-dimension per channel and once across the channel-dimension per 
time bin. I hope this clarifies why the two plots don't show the same.

ICA can also be applied to eye blinks, for which an example is given in 
the "Walkthrough"
http://fieldtrip.fcdonders.nl/walkthrough#using_ica_for_eye_artifact_removal

And of course, ICA can be used for anything else you believe in (e.g. 
look for papers by Makeig)

Best,
Jörn

On 1/4/2012 4:52 PM, qi li wrote:
> Hi,
>
> I am confused about the plot of the z-score and 'most contribute' 
> channel trial plot in the automatic artifact rejection tutorial. The 
> z-score formula provided in the tutorial is  linear to the time course 
> of a particular channel of a specific trial, but the two plots don't 
> look alike.
>
> ICA in the tutorial only applies to ECG, can it be applied to remove 
> eye blink and other known artifacts instead of rejecting trials.
>
> Thanks!
>
> Qi
>
>
>
>
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip


-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Contact:
E-Mail: jm.horschig at donders.ru.nl
Tel:    +31-(0)24-36-68493
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Visiting address:
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NL-6525 EN Nijmegen
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