[Eeglablist] Enough data points for ICA

[Makoto Miyakoshi]

Dear Yamil,

> How to tell if one has a good ICA decomposition?

Dipolar maps indicates you got a good decomposition. See Delorme et al.
(2012) PLoS One. "Independent components are dipolar"

Makoto

On Mon, Jun 8, 2015 at 4:39 AM, Yamil Vidal Dos Santos <
hvidaldossantos at gmail.com> wrote:

> 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
>>
>
>


-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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