[Eeglablist] ICA for eye movement rejection

[Budd, Mary-Jane]

Thanks you fo your replies. This is what I have done so far. Unfortunately, I am left with too few trials. I really need to be able to identify the  remaining components that include eye movements. But I am afraid that if I take these out I may inadvertently remove activity that is of interest. Some components that look like eye movement componenets often have activity across all trials. I guess as I am using a visual presentation this is going to be the case. I will play around with removing these remaining frontal components in the hope that I can identify the eye movements that remain.


On 16/03/2012 08:18, "赵远方" <distancejay at gmail.com> wrote:

Hi Mary-Jane,

As my understanding on the tutorial about ICA-based eye-movement artifact rejection,it advises that we should first reject polluted epochs by naked eyes or by several artifact reject criteria(although this practice is not encouraged in our lab,for every subject's waveform can be quite different).After this,perform ICA for the first time,and then reject the waveform epochs based on every IC,just as in the beginning we treat for the normal epochs.In the last,run ICA again,and directly reject the ICs representing artifacts.Thus we can get the data we have clearest.

Best

在 2012年3月16日 上午3:41，Stephen Politzer-Ahles <politzerahless at gmail.com>写道：
Hello Mary-Jane,

My understanding of this (and what I have been doing for my own datasets) was that the effectiveness of the ICA can be improved by first removing epochs or artifacts that are unrelated to the artifact you're trying to clean up with ICA--for example, when I run ICA to clean up ocular artifacts, I first go through the data and reject epochs with a lot of muscle artifacts or electrode drifts (I guess a similar thing could be accomplished using high- and low-pass filters rather than manual artifact rejection). Then I run the ICA, hopefully get a slightly better decomposition, and proceed to remove the eye-related components and go back through the data to reject any epochs that might have eye movement artifacts remaining after the ICA. But I would also love to hear some more experienced users' take on this issue.

Best,
Steve Politzer-Ahles
Department of Linguistics
University of Kansas


On Thu, Mar 15, 2012 at 11:30 AM, Budd, Mary-Jane <mbudd at essex.ac.uk> wrote:
Dear All,
I know that this has been a much discussed topic but I am rather confused by
some of the responses. I am looking at children's datasets that include many
eye movements (both blinks and  horizontal movements). I have run ICA and
identified eye blinks and distinct muscle artifacts. If I remove these
components and then run an automatic rejection procedure (+-75microvolts on
all electrodes) over half the epochs are rejected due to there still being
eye movements on the eye and frontal electrode channels. I have read that I
should not remove the components but instead scan the components and remove
'noisy' epochs (I assume this means removing epochs where eye blinks are
present). RE-running the ICA will then result in 'cleaner' components which
hopefully will remove the eye movements from my data. I have a couple of
questions regarding this:
1. It would be good to avoid removing epochs as the children blink a  lot
and so I am likely to lose much data.
2. I thought this was the benefit of using ICA for artifact removal as the
components are removed form the data leaving you with all (or as many as
possible) epochs to analyse.
3. What if after the second ICA I am still left with eye movements i.e.
can't clearly identify which component is responsible for the eye movements?

Have I misunderstood something here? Please help,
Mary-Jane

Dr Mary-Jane Budd
Senior Research Officer
Department of Psychology
University of Essex
Wivenhoe Park
Colchester CO4 3SQ
UK

Room 4.726


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Dr Mary-Jane Budd
Senior Research Officer
Department of Psychology
University of Essex
Wivenhoe Park
Colchester CO4 3SQ
UK

Room 4.726