[Eeglablist] ICA decomposition with 128 versus 64 channels?

Sun Jan 22 22:41:15 PST 2006

My apologies  - www.electricfieldsofthebrain.com

Please note that the book itself is not accessible from there,  but  
many figures and quotes are.

On Jan 22, 2006, at 10:10 PM, chaimcit at earthlink.net wrote:

> Can't  access book from given www.electricfieldsoftthebrain....
> Need correct address...
> Dr. Larsen
>
> -----Original Message-----
>> From: ramesh <srinivar at uci.edu>
>> Sent: Jan 22, 2006 3:52 PM
>> To: Joseph Dien <jdien at ku.edu>
>> Cc: eeglablist at sccn.ucsd.edu, Jürgen Kayser  
>> <kayserj at pi.cpmc.columbia.edu>, Matthew Belmonte <mkb30 at cam.ac.uk>
>> Subject: Re: [Eeglablist] ICA decomposition with 128 versus 64  
>> channels?
>>
>> Joe - I think you meant high-pass spatial filter and if you look at my
>> new book - http://www.electricfieldsofthebrain Chapter 8, or 1995  
>> paper
>> in Brain Topography, it is only for surface Laplacians (or I suppose
>> source localization) that the higher channel count is helpful.    
>> Indeed
>> if you want to do surface Laplacians there is potentially more
>> information upto an interelectrode spacing of 2 cm, which would  
>> require
>> more than 180 electrodes.
>>
>> I suspect for PCA, ICA algorithms the same is true, as outlined by
>> Delome in previous emails to this group.
>>
>> If your just going to look at the EP waveforms or spectra at each
>> channel the move from 64 to 128 is only marginally beneficial.  Again
>> see my book, Chapter 7.
>>
>> ramesj
>> On Jan 21, 2006, at 7:05 PM, Joseph Dien wrote:
>>
>>> I dare say it depends on the intended analysis approach.  CSD is, by
>>> its nature, a low-pass filter.  It therefore makes sense to me that
>>> such an approach might not take advantage of a higher channel count.
>>> Given the Srinivasan et al (1996) and the Fletcher et al (1996)
>>> simulation studies, I'm a little surprised by the findings of this  
>>> new
>>> study and look forward to reading it.  However, in my experience as
>>> well, for dipole localization procedures more electrodes are better.
>>>
>>> Cheers!
>>>
>>> Joe
>>>
>>>
>>>
>>> On Jan 20, 2006, at 10:56 AM, Jürgen Kayser wrote:
>>>
>>>> Matthew:
>>>>
>>>> You might be interested in looking at the following article, which
>>>> will be
>>>> published in the February 2006 issue of Clinical Neurophysiology
>>>> (currently
>>>> available via the DOI pointer at Elsevier's web site).
>>>>
>>>> Kayser, J., Tenke, C.E. (2006). Principal components analysis of
>>>> Laplacian
>>>> waveforms as a generic method for identifying ERP generator  
>>>> patterns:
>>>> II.
>>>> Adequacy of low-density estimates. Clinical Neurophysiology, 117(2),
>>>> in
>>>> press.
>>>>
>>>> http://dx.doi.org/10.1016/j.clinph.2005.08.033
>>>>
>>>> Our report investigates the benefits of using high- vs. low-density
>>>> EEG
>>>> montages (129 vs. 31 channels) for typical ERP group data, which is
>>>> likely to
>>>> be relevant to your question. Individual topographic specificity of
>>>> ERP
>>>> components derived from high-resolution ERP/CSD data is largely lost
>>>> in
>>>> ERP group data, because averaging across subjects results in a
>>>> spatial low-
>>>> pass filter. If the focus is on brain processes that can be
>>>> generalized to the
>>>> population under study, there seems to be no immediate gain of
>>>> high-density
>>>> recordings. These findings may come as a surprise as they seem to
>>>> contradict common ERP knowledge based on previous recommendations
>>>> using simulated and individual ERP data. Consequently, a (clinical)
>>>> ERP
>>>> researcher would be well-advised to consider the costs and benefits  
>>>> of
>>>> engaging in high-density EEG recordings.
>>>>
>>>> Best, Jürgen and Craig
>>>>
>>>>
>>>>
>>>> On 18 Jan 2006 at 23:41, Matthew Belmonte wrote:
>>>>
>>>>> I'm in the process of putting together a proposal for an EEG
>>>>> facility, and
>>>>> would like to select hardware with EEGLAB processing in mind.  I'm
>>>>> approaching
>>>>> this from perhaps a bit of a dated perspective: in 1996 I was using
>>>>> only 16
>>>>> channels and homebrewed software for time-frequency analysis, and
>>>>> I've spent
>>>>> the intervening decade working exclusively with fMRI.
>>>>>
>>>>> I've heard from one EEGLAB user that 128 channels don't confer much
>>>>> advantage
>>>>> over 64, since inputs must be spatially downsampled in order to be
>>>>> processed
>>>>> practically on typical computing hardware, and since the  
>>>>> independent
>>>>> components
>>>>> of interest (those from neural sources) don't become much cleaner
>>>>> with 128
>>>>> inputs as compared to 64.  (The tradeoff of spatial resolution and
>>>>> SNR to
>>>>> electrode application time also is a consideration; we'd be
>>>>> recording from
>>>>> autistic children and couldn't afford any great deal of time spent
>>>>> fiddling.)
>>>>>
>>>>> I'd like to hear from EEGLAB users (and developers!) with  
>>>>> experience
>>>>> at 128
>>>>> and/or 64 channels:  Do you find a 64-channel system adequate?   
>>>>> What
>>>>> improvement in data quality has moving to 128 channels given you?
>>>>> If I loaded
>>>>> up a GNU/Linux system with the most RAM that I could get (16GB on  
>>>>> an
>>>>> IBM
>>>>> IntelliStation), would it be able to handle an ICA decomposition of
>>>>> 128-channel
>>>>> data without thrashing, or would I be doubling my investment in
>>>>> amplifiers only
>>>>> to have to mix down 128 signals to 64 before ICA?  And, even if it
>>>>> would be
>>>>> computationally practical, would it be scientifically useful enough
>>>>> to justify
>>>>> the extra preparation time?
>>>>>
>>>>> Many thanks
>>>>>
>>>>> Matthew Belmonte <mkb30 at cam.ac.uk>
>>>>> _______________________________________________
>>>>> eeglablist mailing list eeglablist at sccn.ucsd.edu
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>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>
>>> --------------------------------------------------------------------- 
>>> --
>>> ---------
>>>
>>> Joseph Dien
>>> Assistant Professor of Psychology
>>> Department of Psychology
>>> 419 Fraser Hall
>>> 1415 Jayhawk Blvd
>>> University of Kansas
>>> Lawrence, KS 66045-7556
>>> E-mail: jdien at ku.edu
>>> Office: 785-864-9822 (note: no voicemail)
>>> Fax: 785-864-5696
>>> http://people.ku.edu/~jdien/Dien.html
>>>
>>>
>>> _______________________________________________
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>>>
>> Ramesh Srinivasan
>> Assistant Professor
>> Department of Cognitive Sciences
>> University of California, Irvine
>> Irvine, CA 92697-5100
>>
>>
>> _______________________________________________
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>
>
Ramesh Srinivasan
Assistant Professor
Department of Cognitive Sciences
University of California, Irvine
Irvine, CA 92697-5100