[Eeglablist] ICA decomposition with 128 versus 64 channels?

[Joseph Dien]

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>
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>
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------------------------------------------------------------------------ 
--------

Joseph Dien
Assistant Professor of Psychology
Department of Psychology
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