[Eeglablist] Question - EEGLAB calculating GFP vs FFT

[Makoto Miyakoshi]

Dear Alex,

> I wish to ask how I can determine the total *average* GFP theta z-score
and GFP alpha z-scores similar to the paper below.

I haven't used global field power, but if I remember correctly it is a
simple and well-established method. You should be able to find a technical
paper describing the method.

> And further, can EEGLAB produce graphs as shown in the paper?

No, EEGLAB does not support the time series of GFP plot. Some version of
RORETA was recently supported, but I'm not sure if it is already available.

> Also, how different are GFP and FFT analyses? From what I can understand,
they yield similar results.

The method section of their paper, from a quick scan I made, is pasted
below.

%%%%%%%%%%%%%%%%%%%%%%%%
Analysis. As we identified earlier, The EEG analysis focused on two
segments: (1) the start of each video when the object of the story becomes
apparent and (2) the story segment of each video. Once eye movement and
blink artefacts were removed from the EEG data, the time series data
associated with the start and story segments from the videos were analysed
for all 16 participants and then group-averaged. EEG power spectra were
calculated for theta and alpha (for time series Global Field Power). The
beta bands (17.5-31 Hz) were selected for subsequent LORETA analyses
because of previous literature reporting correlations with regional
cerebral perfusion and cerebral activation
%%%%%%%%%%%%%%%%%%%%%%%%%

Basically, this does not provide sufficient information to replicate their
study. I have no idea how they extracted the specific frequency band.

Makoto



On Fri, Jan 25, 2019 at 10:12 AM Alex Scodellaro <ajscod at gmail.com> wrote:

> Dear all,
>
> I am a junior neuromarketing researcher and am new to the EEGLAB program.
> I have 14 EEG recordings of 2-minute participant exposure to advertisement.
> I have segmented each data-set into 'epochs of interest'.
>
> I wish to ask how I can determine the total *average* GFP theta z-score
> and GFP alpha z-scores similar to the paper below. And further, can EEGLAB
> produce graphs as shown in the paper?
>
> Also, how different are GFP and FFT analyses? From what I can understand,
> they yield similar results.
>
>
> *Gordon, Ross et. al (2017). Using EEG to Examine the Role of Attention,
> Working Memory, Emotion, and Imagination in Narrative Transportation. *
>
>
>
> I would really appreciate any and all help!
>
> Thank you in advance.
> Alex
>
> *Alexander Scodellaro*
> ajscod at gmail.com / 0422211619
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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