Hi, I have been recording EEG data for my research for 1 months now, but I`m comfortable about the EMG artifacts in my EEG data.There are both continues and burst of EMG activity in many subjects` data even after we have shown them how muscle activity will contaminate EEG data and informed them to stay relaxed and try not to move their heads during recording.
I wish to know what are some of the tricks to set up the recording environment (like what kind of chairs should we choose, or is it good to immobilize subjects' heads) to let subjects to stay as relaxed as possible and reduce EMG contamination.
Besides, what are some good ways to remove EMG artifacts from EEG data? I don't really want to simply remove the periods of data with EMG. I have tried ICA but the effect is not satisfactory. I am currently learning CCA (canonical correlation analysis) but have not tried it yet.
By the way, we use 64-channel active electrodes from Brain Product, and we don`t have any EMG/EOG electrodes yet (but we can buy them if necessary).
Thanks in advance.
Hi, difficult to give a general answer without knowing your setup and the appearance and spatial distribution of your artifacts. Anyhow, the first step is always to identify where the artifacts are coming from. In your case, are they from neck or shoulder muscles or perhaps from facial muscles? The spatial distribution is informative and you can also ask the subject to contract certain muscles at time.
We have a brand-new MEG–EEG Primer (by Hari & Puce; Oxford University Press 2017) that has quite an extensive chapter on various kinds of artifacts, in case that you would be interested.
Good luck!
-riitta
Depends on what you need in the processed EEG. You could filter out everything from 22 Hz and up- might do the trick.
The environment and the way you instructed the subjects are possibly producing the contrary effect. The subject must be comfortable and preferably know all the time that he/she is doing a great job. The utilization of EOG/EMG electrodes could be useful to improve ICA by adding extra channels.
Anyway, to obtain a 100% free artifacts recording is not possible. Use short activity periods with resting phases for subjects relaxation allowing him/her to move.
A setup, that we commonly use to reduce artifacts is the utilization of linked ears as reference and linked mastoids as ground, and for conditioning the signals the reference to CAR, after that utilization of any artifact remove technique will achieve better results.
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