[Eeglablist] Calculate ICA on short 'cleaned' epoch, then apply to long epoch

[Xiaoming Du]

Hi all,


I have a rookie question about using ICA to remove specific artifacts. Please correct me if I was wrong.


 (1) I should feed ICA with 'cleaned' epochs (less non-stereotypic noise) and with enough data points (> k*N^2). 
 
 (2), I can calculate ICA on short epochs, then apply the ICA (weights and sphere matrices) to long epochs from the same dateset.


(reference link: http://sccn.ucsd.edu/wiki/Chapter_09:_Decomposing_Data_Using_ICA#Studying_and_removing_ICA_components)


For my data set, I want to remove the known artifacts that occurs right after the events (within 100 ms). Also, there are only 13 channels (including 2 eye-channels) for each subject.

My goal is to remove this special artifacts using ICA on long epochs. However, because I already know the artifacts occurs shortly after events, I want ICA focus on this short window to identify the artifact-components. I want to minimize the effects of other artifacts or noise on ICA. 



My current thoughts are: 1, cut continuous file into long epochs (4 seconds). 

                                     2, remove epochs with non-stereotypic noise.

                                     3, 1-hz high-pass filter the remaining long epochs, then cut short epochs (-30 to 100 ms). In this way, the short epochs mainly contains the artifacts I want to remove. 

                                     4, apply ICA on the 0.13-second short epochs. The sampling rate of our data is 1000 Hz. There are more than 50 trials. Therefore, The data point for ICA are around 1000*0.13*50 = 6500. This is larger than 5070 (30*13^2), so I should have enough data for ICA on those short epochs.

                                     5, identify the artifact-components from step 4.

                                     6, apply the ICA weights and sphere to long epochs (before 1-hz highpass filter), then reject artifact-components identified from step 5. 

                                     7, for now, I should have long epochs that are artifact-corrected and not filtered. 


Please let me know if those steps are reasonable. Any suggestions or comments are appreciated!


Thanks.


Xiaoming
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