[Eeglablist] Interpolate 8 channel montage

[Makoto Miyakoshi]

Dear Brian and Zaeem,

I discussed the validity of the average reference on your '20-40' system. I
wrote 'Some people say no, but I think it is fine' but I was told it is NO.
So let me give you that feedback here.
The reason is described below--this is taken from Electric Field of the
Brain by Nuenz and Srinivasan in p.298. The equation (7.12) referred to
there should be (7.10) which is in p.295. If you want to see the copy of
the page p.295, please let me know.

Makoto

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
...While the average reference offers theoretical as well as practical
advantages, it is effective only if there are a sufficient number of
electrodes (perhaps 64 to 128 or more) distributed over the entire scalp,
including (if practical) samples on the lower surface of the head.
Practical considerations that limit information from the lower surface of
the head include muscle sources and other artifacts. The average reference
is probably a poor choice for use with the standard 10/20 system (Fein et
al. 1988). That is, the first term on the right-hand side of (7.12) is
expected to yield very inaccurate estimates of the surface integral of
potential when sparse electrode arrays are used.

On Thu, Jul 30, 2020 at 12:14 PM Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
wrote:

> Dear Brian and Zaeem,
>
> My first data I analyzed had only seven electrodes.
> Because these electrodes were placed symmetrically to both left-right and
> anterior-posterior axes, it was like an extremely sparse full-scalp
> recording (something like 20-40 system, instead of 10-20)
>
> You can process such data normally except for the following points:
>
>    - Electrode interpolation--could be very rough
>    - Average referencing--Some people say no, but I think it is fine to
>    go ahead if the electrode coverage is more or less uniform across the scalp.
>    - Dipole fitting--the result accuracy (?) is naturally limited, though
>    you tend to see smaller r.v. (why? Because less data needs to be
>    approximated)
>
> In any case, as long as you describe these limitations clearly in your
> report, it is fine.
>
> Makoto
>
>
> On Thu, Jul 23, 2020 at 8:14 AM Kavanaugh, Brian <
> brian_kavanaugh at brown.edu> wrote:
>
>> Zaeem,
>>
>> This is quite useful, thank you very much!
>>
>> Brian
>>
>> On Mon, Jul 20, 2020 at 12:17 PM Zaeem Hadi <zaeemhadi at ymail.com> wrote:
>>
>> > Hi Brian,
>> >
>> > I have been working with 8 channel dataset. However, I have avoided
>> using
>> > the clean_rawdata plugin. The reason being the eye blinks, which are
>> quite
>> > high in amplitude and also present in other channels to some degree. And
>> > thus clean_rawdata would almost always reject 2 or 3 channels. And
>> > interpolating so much data on just 8 channels wouldn't make sense. But
>> if
>> > you have relatively clean data, you might be able to use it.
>> >
>> > To avoid that, I am using the pop_eegthresh(ALLEEG) function to
>> > semi-automatically reject epochs based on amplitude thresholding. For
>> some
>> > reason, it is not available through GUI.
>> >
>> > That being said, I have interpolated some channels in my data due to
>> > excessive noise at the Alpha frequency range, but then I reduced the
>> number
>> > of Independent components being determined using 'pca' option in infomax
>> > ICA, as suggested by Makoto in his pre-processing pipeline.
>> >
>> > Kind Regards,
>> >
>> > Zaeem Hadi
>> >
>> > Brain and Vestibular Group
>> > Imperial College London
>> > On Monday, July 20, 2020, 10:40:00 AM GMT+1, Kavanaugh, Brian <
>> > brian_kavanaugh at brown.edu> wrote:
>> >
>> >
>> > Hi everyone,
>> >
>> > We are hoping to analyze a previously collected dataset that used an 8
>> > channel montage. Does anyone have any experience analyzing such a small
>> > amount of electrodes? We are specifically curious about channel
>> > interpolation options if channels are removed via clean_rawdata. Can we
>> > follow a similar approach that we use for 32/64 channel data? Thanks
>> > everyone!
>> >
>> > Brian
>> >
>> > --
>> > Brian Kavanaugh, PsyD.
>> > Pediatric Neuropsychologist, E. P. Bradley Hospital/Rhode Island
>> Hospital
>> > Assistant Professor (Research), Warren Alpert Medical School of Brown
>> > University
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>>
>>
>> --
>> Brian Kavanaugh, PsyD.
>> Pediatric Neuropsychologist, E. P. Bradley Hospital/Rhode Island Hospital
>> Assistant Professor (Research), Warren Alpert Medical School of Brown
>> University
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>