[Eeglablist] Artifact Rejection
Arnaud Delorme
arno at salk.edu
Thu Jul 28 16:29:52 PDT 2005
Edward Justin Modestino, M.Phil. wrote:
>Hello,
>In the EEGLAB tutorial on artifact rejection, it mentions the default trim
>percentage is 5%. Are there any references for using this default of 5%?
>Or is this based on general statistics of a 95% confidence, or something
>similar?
>
>
This percentage correspond to the percentage of epochs the experimenter
judge to be artifactual. If the data quality is bad, you might want to
increase it, but 10% is usually an acceptable value for most datasets.
>If I were to perform a amplitude thresholding on a channel by channel
>basis, what amplitude in +/- microvolts would be considered an upper
>limit?
>
Yes, you may select specific channels for amplitude thresholding
("electrode(s)" edit box).
>Should this be dynamic and thus be a different microvolt +/-
>amplitude value cutoff for each channel? Are there any reference papers
>for this?
>
>
Usually the same value is used for different (often eye) channels.
>I have one reference Picton et al. (2000), an article about guidelines for
>ERPs which includes recording standards and publication criteria. In this
>article on page 138, it mentions that a criterion level of +/- 200
>microvolts could be used to remove trials. It mentions this may be too
>Conservative for sleep studies which may have higher amplitudes. This +/-
>200 microvolts sounds far too liberal to me. I believe the eye movements
>I have already removed from the data were much less than that!
>
The standard value I use is 50 microvolt although I do not have a
reference at hand. Eye movement amplitude also varies widely from
subject to subject, from probably 30 microvolt to 300 microvolts. For
the purpose of rejecting eye blink artifacts, I think it is better to
adjust this value on a subject to subject basis.
Best regards,
Arno
--
*Arnaud Delorme, Ph.D.*
Swartz Center for Computational Neuroscience, INC, University of San
Diego California
La Jolla, CA92093-0961, USA
*Tel* :/(+1)-858-458-1927 ext 15/
*Fax* :/(+1)-858-458-1847/
*Web page*: sccn.ucsd.edu/~arno <http://www.sccn.ucsd.edu/%7Earno>
*To think upon*:
If I try to be like him, who will be like me?
/Yiddish proverb/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20050728/b712a5bc/attachment.html>
More information about the eeglablist
mailing list