[Eeglablist] automatic artifact rejection

[Makoto Miyakoshi]

Dear Stephen,

Very smart, as usual!

By the way, could you please tell me why you subtract min from max?
> diffs = squeeze( max(EEG.data,[],2) - min(EEG.data,[],2) );

What if you have max 10150 and min 10000?  (after high-pass filtering it is
not likely to happen though)

I thought this would be more straightforward
> diffs = squeeze(max(abs(EEG.data,[],2)));

Am I missing something here? I appreciate your comment. Thank you!

Makoto

On Mon, May 4, 2015 at 9:07 PM, Stephen Politzer-Ahles <spa268 at nyu.edu>
wrote:

> Hi Dana,
>
> I also would have thought these would be implemented, but I couldn't find
> t hem just now; maybe they're in ERPLAB.
>
> It shouldn't be hard, though, to code this yourself. Below is a quick
> sample I just made; I can't guarantee this will work in all cases but it
> gives you an idea. You could easily run some simple code like this and then
> just add the bad trial list into the EEG.reject structure.
>
> Best,
> Steve
>
>
> %%% MAXMIN CRITERION
>
> % Finds the difference between the maximum and minimum of each epoch. Could
> % be tweaked to look only at a certain time range within the epoch
> diffs = squeeze( max(EEG.data,[],2) - min(EEG.data,[],2) );
>
> % We'll kick out any trials whose difference exceeds this uV threshhold
> threshold = 200;
>
> % Find samples that exceed the threshhold
> [chanidx, epochidx] = find( diffs > threshold );
>
> % Find epochs that have at least one sample, at any channel, exceeding the
> % threshhold
> badepochs.maxmin = unique( epochidx );
>
>
>
>
>
>
>
>
>
> %%% NEIGHBORING SAMPLES CRITERION
>
> % Find the difference between neighboring samples each pair of neighboring
> samples
> diffs = arrayfun( @(x)( squeeze (EEG.data(:,x,:) - EEG.data(:,x-1,:) ) ),
> 2:size(EEG.data,2), 'UniformOutput', false );
>
> % organize that cell array into a matrix, which will be easier to work with
> n_chan = size(diffs{1},1);
> n_samp = length(diffs);
> n_trial = size(diffs{1},2);
> diffs = reshape(cell2mat(diffs), n_chan, n_samp, n_trial);
>
> % get the max difference across samples, for each trial
> diffs = squeeze( max(diffs,[],2) );
>
> % We'll kick out any trials whose difference exceeds this uV threshhold
> threshold = 75;
>
> % Find samples that exceed the threshhold
> [chanidx, epochidx] = find( diffs > threshold );
>
> % Find epochs that have at least one sample, at any channel, exceeding the
> % threshhold
> badepochs.neighbsamp = unique( epochidx );
>
>
>
> Stephen Politzer-Ahles
> New York University, Abu Dhabi
> Neuroscience of Language Lab
> http://www.nyu.edu/projects/politzer-ahles/
>
> On Thu, Apr 30, 2015 at 12:37 PM, Son, D.M.E. van <
> d.m.e.van.son at fsw.leidenuniv.nl> wrote:
>
>>  Dear Eeglab members,
>>
>> Before manually selecting artifacts in my data, I would like to
>> pre-select artifacts automatically. I have seen that Eeglab provides an
>> automatic epoch rejection toolbox, but specific epoch selection that I
>> would like to make, does not seem to be provided.
>> e.g.; I would like to remove epochs where the difference between the
>> maximum and minimum in an interval of a selectable length, and the
>> difference between the maximum and minimum in the epoch itself, exceeds a
>> specific value. Also, I’d like to remove epochs wherin the absolute
>> difference between two neighboring sampling points exceeds a certain
>> value.
>>
>> Does anyone have an idea if this is possible in Eeglab automatically? Or
>> perhaps it is possible that I script this separately?
>>
>> Many thanks in advance
>>
>> Dana
>>
>>
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>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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