[Eeglablist] How to deal with 1/f noise in

Gangadhar Garipelli gangadhar.garipelli at epfl.ch
Mon Nov 15 01:08:49 PST 2010

Hello Phil,

I guess you are speaking about cross-frequency coupling [1]!
If that is so, thanks a lot for reinforcing me that I am moving in right 
direction! :-)
And I hope this not to consume infinite time!

However, I would like to figure out the complete limits of low-frequency 
features for real-time experimental manipulations.



On 11/15/10 1:16 AM, Philip Michael Zeman wrote:
> Hello Gangadhar
> If you have infinite time (or grad students): something for you to try:
> you might also try looking at higher frequencies for this signal you 
> search for at the low end of the spectrum.  I'm finding that some of 
> these low frequencies signals are related to high-frequency signals.  
> It makes some sense if you subscribe to the idea that alot of these 
> signals are resulting from non-linear mixing.  For example, in a study 
> a few years back, I was tracking theta-band activities.  In my search, 
> I also check to see if I could find some theta-band modulated 
> activities in the gamma frequency band. (Like a low frequency signal 
> multiplied with a higher frequency carrie wave.)  I did find 
> statistically significant differences between conditions this way but 
> demodulating the signal (assuming a gamma band carrier frequency).
> Phil
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Philip Michael Zeman B.Eng, Ph.D.
> Applied Brain and Vision Sciences Inc.
> Brain Function Analysis for Novel Paradigms and Serious Games
> Analysis of Pharmaceutical Effects on Brain Function
> http://www.abvsciences.com
> Latest Brain Research Result:
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> Email:   pzeman at alumni.uvic.ca
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> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Gangadhar Garipelli <gangadhar.garipelli at epfl.ch>
> ----- Original Message ----- From: "Gangadhar Garipelli" 
> <gangadhar.garipelli at epfl.ch>
> To: "Arnaldo Batista" <agb at fct.unl.pt>
> Cc: <eeglablist at sccn.ucsd.edu>
> Sent: Friday, November 12, 2010 6:36 AM
> Subject: Re: [Eeglablist] How to deal with 1/f noise in
>> Hello Arnaldo,
>> Thanks for the attempt! :-)
>> Yes, it is a bit tricky to record such slow oscillations. Conventional
>> or classical-EEG is usually high pass at 0.5Hz. However, FbEEG is
>> becoming a standard. Please check Vanhatalo et al, 2005 [1] for an
>> excellent report on FbEEG and hardware (using DC coupled amplifiers)
>> other related requirements.
>> Reference :
>> [I] Vanhatalo S, Viopio J, Kaila K. Full-band EEG (FbEEG): An emerging
>> standard in electroencephalography. Clin. Neurophysiol., 116(1):1-8, 
>> 2005.
>> On 11/12/2010 03:04 PM, Arnaldo Batista wrote:
>>> Hi
>>> Can´t help you, but thought being generally the EEG data high-pass 
>>> filtered
>>> in the acquisition step, and how can you retain signal at such low
>>> frequencies?
>>> Thanks
>>> Arnaldo
>>> -----Original Message-----
>>> From: eeglablist-bounces at sccn.ucsd.edu
>>> [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Gangadhar 
>>> Garipelli
>>> Sent: 05 November 2010 11:51
>>> To: eeglablist at sccn.ucsd.edu
>>> Subject: [Eeglablist] How to deal with 1/f noise in the low frequency
>>> oscillations for on-line experiments?
>>> Dear all,
>>> I work with low frequency oscillations of the brain while a human
>>> subject is cognitively engaged in a task. From the off-line analysis
>>> (using zero-phase band pass FIR filters on full-band EEG), I discovered
>>> that task-related cognitive signals are located in the range of [0.2
>>> 0.3]Hz and in [0.6 0.8]Hz. The fluctuations/oscillations ( formally
>>> called very low frequency oscillations VLFO, or infra slow oscillations
>>> ISO) below 0.2Hz are REAL devil due to 1/f nature. The noise power is
>>>> 100 times higher than signal's power.
>>> Now as per my experimental demands, I need to estimate on-line in
>>> real-time the signals mentioned in the above range and manipulate
>>> stimulus presentation. Ideally, this eventually means I need to have a
>>> very sharp high pass filter with almost zero group/phase delay. Which
>>> sounds impossible!
>>> However, I should come up with a decent trade-off between SNR and
>>> phase-delay. Do you have any suggestions? All suggestions ranging from
>>> signal processing/machine-learning to hardware to solve this problem 
>>> are
>>> most welcome!
>>> Thanks in advance!
>>> Sincerely,
>> -- 
>> Gangadhar GARIPELLI,
>> Doctoral assistant,
>> ELB 141, Station-11,
>> CH-1015, Lausanne, Switzerland.
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Gangadhar GARIPELLI,
Doctoral assistant,
ELB 133, Station-11,
CH-1015, Lausanne, Switzerland.

Tel : +41-21-6936985
Fax : +41-21-6935305
gangadhar.garipelli at epfl.ch

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