Hello,
I’m still looking into details about the (temporal-)spectral analysis I can apply to EEG data, and for now, I am focusing on the delta-band (1, 4) Hz and alpha-band (8, 13) Hz on long epochs (8s, 16s or 24s). The dataset is sampled at 512 Hz and filtered between 1. and 40. Hz.
PSD
multitaper
From my limited knowledge, multitaper method provides a more robust spectral estimation than welch’s periodograms, but is more computationally expensive. But the bandwidth smooths together frequencies in a large range. The default, 4 Hz, will smooth together frequencies at ± 4 Hz around each frequency. Is this potentially an issue when looking at low frequencies, namely delta and alpha bands? Would you recommend a different half-bandwidth value?
welch
If I choose to go this way instead of multitapers, as the lowest frequency I am interested in is 1 Hz, I guess the welch’s segment length should be set to a 1-second minimum. Is this assumption correct? Would you set it to more, e.g. 2 seconds?
With a 1-second minimum, on 8 seconds epochs, I could get 8 segments without overlap, or way more with overlap. Besides the added computational load, increasing the number of segments via a large overlap should improve the spectral estimate, correct?
TFR
This time I am interested in 24 seconds long epochs. This dataset is from a neurofeedback study, thus the temporal resolution isn’t crucial as there isn’t a stimuli onset. I have the temporal resolution set to 2 seconds, i.e. n_cycles = 2 * freqs.
For the methods, I experimented mostly with multitapers for now, but would you recommend using Morlet wavelets for low-frequencies?
For the frequencies of interest, I have it set at np.arange(1., 15., 1):
- 1 Hz because this is the high-pass cut-off frequency.
- 15 Hz, because I was aiming for 13 Hz (upper limit of my defined alpha-band) + half-bandwidth (with multitapers). Is this a good idea, or would you provide a different range of frequencies of interest?
Also, what should impact the decision about the granularity of the frequencies of interest? 1 Hz? half-bandwidth in the case of multitapers? Something else?
This is already a lot of questions on the computation part, I haven’t found a consensus on settings to use for those common bands (other than the defaults), and I am a bit struggling in figuring out what should weigh my decisions.
Looking forward to some input!