[FieldTrip] problem with ICA

[Eelke Spaak]

Hi Hweeling,

To add to Aaron's explanation, you can instruct the algorithm to use a
subspace projection of your data by specifying cfg.runica.pca = N,
where N is the rank of your data (in your case 119, it seems).

Best,
Eelke

On 16 January 2014 13:42, Aaron Schurger <aaron.schurger at gmail.com> wrote:
> Sounds like you may have done something to your data, like
> interpolating channels, before you ran ICA. It is OK to filter your
> data before running ICA, and some other operations are OK too, but if
> you do anything that mixes activity from different channels in any
> way, then you can run into problems with ICA (and results from ICA can
> be invalid).
> Aaron
>
> On Thu, Jan 16, 2014 at 1:22 PM, Hwee Ling Lee <hweeling.lee at gmail.com> wrote:
>> Dear all,
>>
>> I've collected data using a 128 channel EEG cap, and I tried to perform ICA
>> on the data. However, I got an error message with fieldtrip on Matlab.
>> Here's the error message:
>>
>> the input is raw data with 127 channels and 1 trials
>> selecting 123 channels
>> baseline correcting data
>> scaling data with 1 over 148.247820
>> concatenating data.
>> concatenated data matrix size 123x2789000
>> starting decomposition using runica
>>
>> Input data size [123,2789000] = 123 channels, 2789000 frames/nFinding 123
>> ICA components using logistic ICA.
>> Decomposing 184 frames per ICA weight ((15129)^2 = 2789000 weights, Initial
>> learning rate will be 0.001, block size 75.
>> Learning rate will be multiplied by 0.9 whenever angledelta >= 60 deg.
>> More than 32 channels: default stopping weight change 1E-7
>> Training will end when wchange < 1e-07 or after 512 steps.
>> Online bias adjustment will be used.
>> Removing mean of each channel ...
>> Final training data range: -3.46556 to 6.39436
>> Computing the sphering matrix...
>> Starting weights are the identity matrix ...
>> Sphering the data ...
>> Beginning ICA training ...
>> Data has rank 119. Cannot compute 123 components.
>> the call to "ft_componentanalysis" took 148 seconds
>>
>> Could someone please let me know what went wrong?
>>
>> Thanks!
>>
>> Cheers,
>> Hweeling
>>
>>
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>
>
>
> --
> Aaron Schurger, PhD
> Senior researcher
> Laboratory of Cognitive Neuroscience
> Brain-Mind Institute, Department of Life Sciences
> École Polytechnique Fédérale de Lausanne
> Station 19, AI 2101
> 1015 Lausanne, Switzerland
> +41 21 693 1771
> aaron.schurger at epfl.ch
> http://lnco.epfl.ch/
>
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