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

Philip Michael Zeman pzeman at alumni.uvic.ca
Sun Nov 14 16:16:51 PST 2010


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

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Philip Michael Zeman B.Eng, Ph.D.
Applied Brain and Vision Sciences Inc.
Brain Function Analysis for Novel Paradigms and Serious Games
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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,
> EPFL-STI-CNBI,
> ELB 141, Station-11,
> CH-1015, Lausanne, Switzerland.
>
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