[Eeglablist] Oddly "Wavy" Data

[tognoli at ccs.fau.edu]

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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