[Eeglablist] Enough data points for ICA

[Yamil Vidal Dos Santos]

Hi Makoto,
Thank you for your answer.
Now a related and very basic question. How to tell if one has a good ICA
decomposition?
Thanks,
Yamil

On Mon, Jun 8, 2015 at 2:15 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
wrote:

> Dear Yamil,
>
> ICA would work well even with relatively less number of datapoints if data
> are stationary (i.e. data from repeated trials and nothing else) with no
> too large amplitude.
>
> You mean you have 128ch but only 7-min long data? Hmm that is quite a
> concern for me. You may try 'pca', 40 (or around) to see if this dimension
> reduction improves the results... if it does, then you'd better use pca
> option for the final analysis.
>
> The formula of (ch^2)x30 was empirically derived, and there is no
> quantitative experiment on it. So the issue is ambiguous.
>
> I recently updated my wiki page about this issue. It is my personal
> opinion. In short, "Someone please investigate this issue."
>
> Makoto
>
> http://sccn.ucsd.edu/wiki/Makoto%27s_preprocessing_pipeline
>
> "...By the way, how many datapoints do we need to obtain good ICA results?
> We have been suggesting that there needs to be (number of channel)^2 x 20
> to 30 data points for the case of running ICA on 32 channels, and the
> number ’20 to 30’ should increase as the number of channels increase.
> However, we have not performed a systematic investigation on the minimum
> number of data points required for ICA. I personally downsample the data
> (with more than 128 channels) to 128Hz, particularly when I need to give up
> gamma due to too strong 50/60Hz for cleanline, only for ICA just to obtain
> the decomposition matrix. In this case, the number of datapoints is
> absolutely lower than the number suggested by the formula, but I have not
> encountered any problem so far. Some of my colleagues even told me that the
> aggressive downsampling before ICA enhanced the decomposition quality. This
> makes sense because most interesting EEG phenomena occur below 50 Hz
> anyways. I can easily imagine it is nonsense to use 192kHz sampling rate to
> record 1-sec long 64-ch EEG data and expect a good ICA results out of it...
> so probably it is not the absolute number of data points that determines
> the quality of decomposition. Similarly, it is probably true that ICA on
> 512Hz-sampled data is not necessarily better than ICA on the same data
> downsampled to 256Hz simply because the former has twice as many
> datapoints. Someone please investigate this issue."
>
> On Thu, Jun 4, 2015 at 1:42 AM, Yamil Vidal Dos Santos <
> hvidaldossantos at gmail.com> wrote:
>
>> Hi all,
>> I have seen in this list that the recommended minimum data points to run
>> ICA is channel^2 x 30.
>> If I have a 128 electrode montage, and I sample at 250Hz, this would mean
>> a minimum of 32 minutes of recording. Is this correct? Would it make a
>> difference if I use PCA with ICA?
>>
>> I'm asking this because in one of my experiments the entire recording
>> lasts about 7 minutes. I wanted to use ICA to clean this data, because the
>> experiment doesn't have a trial structure, but is instead a continues
>> exposure to a speech stream. I have run ICA on this data before and the
>> results looked decent.
>> Any recommendations?
>>
>> Thanks,
>> Yamil
>>
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
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