[Eeglablist] Inquiry about clean_artifacts.m function

[ibrilmay at uni-koeln.de]

Hi,

This topic comes up repeatedly on the list. There is a publication by  
the mobilab people from Berlin  
(https://urldefense.com/v3/__https://www.biorxiv.org/content/biorxiv/early/2022/10/06/2022.09.29.510051.full.pdf__;!!Mih3wA!D-VayU4D76htcPMSpfjj3jbRjEeNEUyjoVHHm3sG2_4CyNjLKMgVDLn2kFQ7hSWkS4HxjBNNB1gymhv2PNr2olAQWpU$ ), that  
says:
"Subsequently, we repeatedly run the clean_artifacts function of the  
clean raw data EEGLAB plugin, with the number of repetitions specified  
by the bemobil_config.chan_detect_num_iter parameter. This is  
necessary because clean_artifacts uses a random sample consensus  
(RANSAC) approach that does not necessarily converge to the same  
results when repeated. The function stores the sampling in a micro  
cache that will be accessed when restarting the function without  
restarting MATLAB or clearing the micro cache beforehand, resembling a  
stable result. But  hen using the function with a cleared micro cache,  
the detected channels might differ. To ensure a reproducible  ad  
channel detection, we thus clear the micro cache and repeat the  
detection several times, with a recommended minimum of 10 iterations.  
Only channels that were flagged as ‘bad’ more than a given proportion  
of the processed data (specified in  
bemobil_config.chan_detected_fraction_threshold) are then detected for  
final removal. We exclude all EOG channels from the detected bad  
channels because their statistical properties will often lead to false  
positive detection."

Maybe this is something you might want to look into.

Best
Ingmar

Zitat von Velu Prabhakar Kumaravel <velu.kumaravel at unitn.it>:

> I think it is the RANSAC algorithm that produces inconsistent removals. You
> might take a look at Makoto's page here
> <https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Channel_rejection_using_RANSAC_in_clean_rawdata.28.29_.2803.2F21.2F2022_added.29>
> .
>
> Best,
>
> Velu Prabhakar Kumaravel, PhD Student
> Center for Mind/Brain Sciences,
> University of Trento, Italy
>
>
> On Mon, 23 Jan 2023 at 17:07, Charalampos Georgios Lamprou <
> 100063082 at ku.ac.ae> wrote:
>
>> Dear EEGLAB developers,
>>
>> I hope this mail finds you well.
>>
>> My name is Charalampos Lamprou and I am currently working on EEG analysis,
>> using EEGLAB. I would like to inquire about the clean_artifacts function
>> and the way it works. I have noticed that even though I give as input the
>> same data and using the same parameters, I don't always recieve the same
>> results. In particular, in each realisation the function removes different
>> channels. Hence, I would like to ask if the the function works in a
>> stochastic way and if so, where exactly the stochasticity lies and why in
>> different realisations, different channels are rejected.
>>
>>
>> Thank you in advance!
>>
>>
>> Kind regards.
>>
>>
>> Charalampos Lamprou
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