[Eeglablist] Is average reference not recommended on 10-20 system?

Mon Jul 24 07:10:30 PDT 2023

Hi, you might try:

@article{lepage2014statistically,
  title={A statistically robust EEG re-referencing procedure to
mitigate reference effect},
  author={Lepage, Kyle Q and Kramer, Mark A and Chu, Catherine J},
  journal={Journal of neuroscience methods},
  volume={235},
  pages={101--116},
  year={2014},
  publisher={Elsevier}
}

https://urldefense.com/v3/__https://www.mathworks.com/matlabcentral/fileexchange/64643-apply-rcar/?s_tid=LandingPageTabfx__;!!Mih3wA!DnegK98ehdTXFqLwanApFI6uX5CRADC5cc0HYGAMKvej1yK8Dq8xPj0PAXwHyWmXP_RdnbAgdJjXQmHz3Yx67WF9Pw$ 

Best,

  Kyle

On Fri, Jun 16, 2023 at 12:09 PM Cedric Cannard via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Hi Makoto,
>
> This is basically what I was referring to yes. Doesn't this paragraph you
> sent support this recommendation?
>
> "As the number of electrodes increases the error in the approximation is
> expected to decrease. [...] with large numbers of electrodes (say
> 128 or more), we have found that the average reference often performs
> reasonably well as an estimate of reference-independent potentials in
> simulation studies (Srinivasan et al. 1998)."
>
> However, I should have provided a more nuanced response. Both average and
> REST/ininfity references are both considered superior to all other known
> references, especially with 64+ channels. However, I now tend to recommend
> and use REST because, while it faces the same limitations caused by low
> electrode coverage and density (i.e., spherical harmonics degree < 7 with
> less than 128 channels; Srinivasan et al. 1998), the error can be reduced
> as the head model improves. See here for great discussion on this:
> https://urldefense.com/v3/__https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2967671/__;!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMhzKOjCew$
>
> "idealized simulations (Marzetti et al, 2007; Qin et al, 2010) where the
> head model used to estimate G is very similar to model used to estimate
> errors, REST outperforms AVE. From this argument we see that the choice
> between AVE and REST largely boils down to questions of genuine head model
> accuracy [...]. The most popular head model consists of 3 or 4 concentric
> spherical shells representing, brain, CSF, skull, and scalp tissue (Rush
> and Driscoll, 1969; Nunez, 1981; Nunez and Srinivasan, 2006). The spherical
> symmetry allows for relatively simple analytic solutions to the forward
> problem. On the other hand [...], despite these limitations, simple head
> models can be extremely useful, typically by proving that many EEG analysis
> methods proposed over the past 50 years or so will NOT work. For example,
> the so-called quiet reference myth is easily discredited with simple models
> (Rush and Driscoll, 1969; Nunez, 1981; Nunez and Westdorp, 1994; Nunez and
> Srinivasan, 2006). Or, distortion by reference and volume conduction is
> shown to produce very large errors in scalp coherence estimates (Nunez et
> al, 1997, 1999; Srinivasan et al, 1996, 1998; Marzetti et al, 2007).
> Moderate head model inaccuracy does not change the central conclusions of
> these studies. Simulations using simple head models then provide a critical
> “filter” through which mathematical methods must first pass to be
> considered further by serious scientists. We must be continually reminded
> that fancy mathematics can never trump physical principles. The Qin et al
> (2010) study has passed this important first test by showing that REST
> works with simple head models and certain assumed source distributions, but
> its accuracy with read heads and other source distributions is unknown. For
> this reason, I suggest that REST and AVE be adopted as reference partners,
> at least until better information becomes available."
>
> In conclusion, they are similar, but REST seems to be the most promising
> in the long term (along with Surface Laplacian methods), as the head models
> improve. It already performs slightly better than AVE (e.g.,
> https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/abs/pii/S1388245710004153__;!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMhgoEdbtw$
> and
> https://urldefense.com/v3/__https://www.frontiersin.org/articles/10.3389/fnins.2017.00205/full?ref=https:**Agithubhelp.com__;Ly8!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMg1UjXsBA$
> ), and will keep improving over the years. That's why I tend to use it and
> recommend it now.
>
> Additionally, REST (and especially the new regularized REST) may present
> new advantages (e.g., the effective rank deficiency issue although this is
> pretty much solved now with the recent solution, data recorded with
> monopolar reference, etc.). See:
>
> https://urldefense.com/v3/__https://link.springer.com/article/10.1007/s10548-019-00706-y__;!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMjinh8EZg$
>
> https://urldefense.com/v3/__https://iopscience.iop.org/article/10.1088/1741-2552/aaa13f__;!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMhHPAIx-Q$
>
> https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/S1388245723005941__;!!Mih3wA!GHxYARW27MxFaJ2eDEyohyAmJb8T3foIM3Ee70lzdOc35_OV2YZVDGWwy4ZnfyPRe7E06ijETkbzKxADMMiRFwJb5w$
>
> Note that the EEG reference conversation will go to infinity ;)
>
> Cedric
>
>
> Sent with Proton Mail secure email.
>
> ------- Original Message -------
> On Thursday, June 15th, 2023 at 2:25 PM, Makoto Miyakoshi via eeglablist <
> eeglablist at sccn.ucsd.edu> wrote:
>
>
> > Dear Jinwon and Cedric,
> >
> > Let's confirm the problem first. 'Electric Fields of the Brain' by Nunez
> > and Srinivasan (2006) (hereafter EFB) p.295 says:
> >
> > ...The surface integral of the potential over a volume conductor
> containing
> > dipole sources must be zero as a consequence of current conservation
> > (Bertrand et al. 1985). In this case, the surface integral can be
> estimated
> > by the second term on the right-hand side of (7.10); that is, by
> averaging
> > the measured potentials and changing the sign of this average. (...)
> Since
> > we cannot measure the potentials on a closed surface surrounding the
> brain,
> > the first term on the right-hand side of (7.10) will not generally
> vanish.
> > The distribution of potential on the underside of the head (within the
> neck
> > region) cannot be measured. Furthermore, the average potential for any
> > group of electrode positions, given by the second term on the right-hand
> > side of (7.10), can only approximate the surface integral over the volume
> > conductor. For example, this is expected to be a very poor approximation
> if
> > applied with the standard 10/20 electrode system. As the number of
> > electrodes increases the error in the approximation is expected to
> > decrease. Thus, like any other choice of reference, the average reference
> > provides biased estimates of reference-independent potentials.
> > Nevertheless, when used in studies with large numbers of electrodes (say
> > 128 or more), we have found that the average reference often performs
> > reasonably well as an estimate of reference-independent potentials in
> > simulation studies (Srinivasan et al. 1998).
> >
> > So the problem is that the difference between the real average and
> > electrode-sampled average becomes worse, and it is actually very bad when
> > you are using 20 channels supported by 10-20 systems.
> >
> > Cedric, I do not see they are against using average reference when < 128
> > ch. Did you find that description elsewhere from the book?
> >
> > Jinwon, that said, from the linear algebraic point of view, it makes no
> > sense to say one choice of reference electrode, including average of
> > arbitrary combinations of electrodes, is 'worse' than another.When you
> use
> > average reference with low number of electrodes (say 20 or 30), you may
> be
> > criticized that your electrode average is severely deviated from the true
> > surface average. But using average reference does not mean you are
> making a
> > claim that your electrode average at a given frame be zero. Compared with
> > using Fz, Cz, Pz, or (digitally linked) mastoid/earlobe (physically liked
> > mastoid/earlobe is out of question) as a reference electrode, your
> average
> > potential may be still useful for certain purposes. Clarifying the merit
> of
> > using average reference in your case over other choices of reference
> > requires elaborated simulations which may not be easy or even realistic.
> > But my point is that blindly following the rule 'average reference
> applied
> > to less than 64 ch == bad' is ridiculous. For example, depending on your
> > targeted EEG phenomenon, if it has a dominant low spatial frequency,
> > relatively low spatial sampling by a relatively low number of electrodes
> > (which is hopefully uniformly distributed) could be more tolerable.
> >
> > If your reviewer does not write much comment on your experimental design
> or
> > result interpretation but just writes this kind of general and trivial
> > technical things about EEG, that is not a good reviewer. Send me the
> > reviewer's comment in a separate email and I can assess it further for
> you.
> >
> > Makoto
> >
> >
> >
> >
> > On Thu, Jun 15, 2023 at 1:35 PM 장진원 via eeglablist
> eeglablist at sccn.ucsd.edu
> >
> > wrote:
> >
> > > Dear all,
> > >
> > > One of my reviewers has suggested that because average reference
> relies on
> > > the assumption that the electrode coverage represents a sphere, it is
> not
> > > good to average-reference with electrodes less than 64. I have used the
> > > average-referencing as recommended on
> > >
> > >
> https://urldefense.com/v3/__https://eeglab.org/tutorials/05_Preprocess/rereferencing.html__;!!Mih3wA!D_yQ2dwBfLAhlMiue98MMVMBa2NNnbOxZRm_SDLtYScegpGg5wR7Ly9SmCRGov3uc7pP5TS6NKxNf9Zs2cdtn560dQ$
> > > , so I wonder
> > > what could be the alternative.
> > >
> > > Best Regards,
> > > Jinwon Chang
> > > _______________________________________________
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