[Eeglablist] How to deal with 1/f noise in the low frequency oscillations for on-line experiments?

Gangadhar Garipelli gangadhar.garipelli at epfl.ch
Fri Nov 5 04:50:44 PDT 2010

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!
Gangadhar GARIPELLI,
Doctoral student,
EPFL, Switzerland

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