[Eeglablist] Oddly "Wavy" Data

Matthew Stief ms2272 at cornell.edu
Mon Feb 27 14:38:54 PST 2012 

Thank you very much for your attention.  It's a bit embarressing but to be
frank I was mainly worried it signified I'd done something wrong in running
the participant, or something of the like, and was artifactual in nature.
Naive of me of course, I appreciate your input.

As long as it's not artifactual it shouldn't be a problem for what I want
with these data.

-M


On Mon, Feb 27, 2012 at 5:15 PM, <tognoli at ccs.fau.edu> wrote:

> Dear Matthew,
>
> From  the figures that you sent, it seems to me that you deal with two
> noticeable sets of rhythmic activities:
> -The channels placed on the upper part of the figure carry some typical
> alpha frequency. You have a good view onto them from time marker 520.5 to
> 522 and again later at time marker 524. If you count the interval between
> two peaks, you should see (for this subject) a ~10-11Hz. The topography
> would tell you which of several 10Hz activities you are dealing with, e.g.
> alpha, mu or others.
>
> -There is also another activity that is prominent across a broad range of
> channels at time markers 522-523, much slower in the theta range (roughly
> ~6Hz). More information on its spatial distribution would be necessary to
> draw some hypotheses about its significance.
>
> With kind regards,
> ______________________________________________
>
> Emmanuelle Tognoli - PhD
> http://www.ccs.fau.edu/~tognoli
> Center for Complex Systems and Brain Sciences
> Florida Atlantic University
>
> > Thanks Steve/Tarik/Andrew,
> >
> > Of course it's alpha!  I knew it would be something stupid and elementary
> > like that.  My EEG education so far has been very narrow, basically I've
> > just been learning everything I need to know to troubleshoot this study
> as
> > issues arise.
> >
> > I should have known given how incredibly mind numbingly boring my study
> > is.
> >
> > Thanks again.
> >
> > -Matthew
> >
> >
> >
> > On Mon, Feb 27, 2012 at 2:56 PM, Stephen Politzer-Ahles <
> > politzerahless at gmail.com> wrote:
> >
> >> Hi Matthew,
> >>
> >> To me this looks a bit like alpha waves (common when a subject is
> >> getting
> >> tired, shutting their eyes, about to doze off, etc.) but I can't really
> >> be
> >> sure. I can't read the channel labels in your images, but alpha waves
> >> tend
> >> to show up the most robustly on posterior channels, so that would be one
> >> way to tell if that's what they are. If it is alpha waves, there are
> >> different opinions out there about what to do with them. Some
> >> experimenters
> >> usually reject stretches with alpha waves, whereas others believe they
> >> can
> >> often be left in if they're not too big (I believe Steve Luck's (2005)
> >> book
> >> has more information about this in the chapter on artifact rejection; I
> >> don't have a copy handy right now so I don't remember exactly what it
> >> says). In our lab we never try to remove them by filtering, because they
> >> tend to be in more or less the same frequency range as the
> >> (language-related) cognitive activity we're interested in; I'm not sure
> >> what frequency ranges you're interested in so I'm not sure if filtering
> >> would be appropriate or not. In my experience, alpha waves of about this
> >> size have seemed to get more or less averaged out of the ERPs if there
> >> are
> >> enough trials, but others on the list may be able to give more feedback.
> >>
> >> Good luck,
> >> Steve Politzer-Ahles
> >>
> >> On Mon, Feb 27, 2012 at 7:56 AM, Matthew Stief <ms2272 at cornell.edu>
> >> wrote:
> >>
> >>> Hi Everyone,
> >>>
> >>> I was wondering if anyone has had any experience with the "wavy"
> >>> activity that seems to go across almost all of the channels in this
> >>> subjects data.   I am sure it is familiar to you but I have not seen it
> >>> in
> >>> any of the text books or guides I can find online and don't have an
> >>> experienced person supervising me.
> >>>
> >>> Here's what the strange activity looks like in filtered, cleaned,
> >>> epoched, and baselined data...
> >>>
> >>>
> >>>
> http://s1153.photobucket.com/albums/p512/mstief/?action=view&current=wavychannels7.jpg
> >>>
> >>>
> >>> Going back to the same dataset before any processing has been done, you
> >>> can see the same waves.  Obviously this is not particularly clean data,
> >>> but
> >>> is it salvageable?
> >>>
> >>>
> >>>
> http://s1153.photobucket.com/albums/p512/mstief/?action=view&current=wavychannels8.jpg
> >>>
> >>>
> >>> Here's the exact same stretch of data after it has gone through 1hz
> >>> high
> >>> pass and 55hz low pass filters.
> >>>
> >>>
> >>>
> http://s1153.photobucket.com/albums/p512/mstief/?action=view&current=wavychannels10.jpg
> >>>
> >>>
> >>> It does seem to be affecting the ERPs at least to my untutored eye,
> >>> here's one channel.
> >>>
> >>>
> >>>
> http://s1153.photobucket.com/albums/p512/mstief/?action=view&current=wavychannels4.jpg
> >>>
> >>>
> >>> So what is it?  Normal?  Horrible?  Fatal or merely deleterious?  Given
> >>> that it seems to contaminate most or all of the data for this person
> >>> should
> >>> I just throw it out or can I get something out of it?  In particular
> >>> how
> >>> will ICA handle it?  Do I still have a chance of getting a stable
> >>> decomposition out of it with a reliably identifiable P1?  This person
> >>> was
> >>> particularly bad but there are less drastic examples in several of my
> >>> other
> >>> participants.  Keep in mind some of my participants are rather rare and
> >>> would be difficult to replace (I study sexual orientation and some
> >>> varieties are less common than others).
> >>>
> >>> --
> >>> _________________________________________________________________
> >>> Matthew Stief
> >>> Human Development | Sex & Gender Lab | Cornell University
> >>> http://www.human.cornell.edu/HD/sexgender
> >>>
> >>>
> >>> Heterosexuality isn't normal, it's just common.
> >>> -Dorothy Parker
> >>>
> >>> _______________________________________________
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> >>>
> >>
> >>
> >>
> >> --
> >> Stephen Politzer-Ahles
> >> University of Kansas
> >> Linguistics Department
> >> http://www.linguistics.ku.edu/
> >>
> >
> >
> >
> > --
> > _________________________________________________________________
> > Matthew Stief
> > Human Development | Sex & Gender Lab | Cornell University
> > http://www.human.cornell.edu/HD/sexgender
> >
> >
> > Heterosexuality isn't normal, it's just common.
> > -Dorothy Parker
> >
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-- 
_________________________________________________________________
Matthew Stief
Human Development | Sex & Gender Lab | Cornell University
http://www.human.cornell.edu/HD/sexgender


Heterosexuality isn't normal, it's just common.
-Dorothy Parker
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