Has anyone tried this before? Normally facial EMG is done with bipolar electrodes. Will having 2 unipolar electrodes and then subtracting the difference be okay? I've read that the bipolar electrodes are positioned only a centimeter apart, but this seems hard with the bulkier EEG unipolar ones. Will 2 cms apart work as well? What to do with the remaining unused EEG electrodes? Do I switch them off or may they be simply ignored? Help much appreciated!
I think it would largely depend on what other equipment you are using, in particular the amplifier. A differential amplifier will remove signals common to both electrodes, and a unipolar amp will not. I don't have any experience in using the equipment you mentioned but I think you could use a unipolar configuration with electrodes 2cm apart, a reference electrode placed elsewhere and measure the difference between the 2. However you may find you have a lot of 50hz noise.
HI. Yes, it is possible. You can deactivate the electrodes that you don't need. There might just be an issue with the reference montage. Are you also using QuickAmp?
Further, bipolar electrodes are placed 2cm apart for signal detection reasons. They measure the difference between both poles (if i'm not mistaken) and voilá, that's your signal. Unipolar, uses as reference some other way, such a common average reference to which all electrodes signal is referenced to.
I'm not sure about subtraction the signal from 2 bipolar electrodes because they have already been referenced to something while recording. Please read this: http://www.bem.fi/book/13/13.htm
It is possible theoretically but you should be very careful with the amp you are using. (To be honest I discourage it, It has been already tried in my lab and it failed). You have to keep in mind that the signal picked up during facial muscles EMG recording is very small. Bipolar electrodes allows for using a differential amplifier and reduce noise. By using unipolar elecrodes you would probably have a terrible signal to noise ratio.
The main reason I believe for placing the electrode at a distance of 1cm is to reduce any cross-talk. i.e. since the muscle is very small (Unless your subjects have huge faces). you are gonna pick up the activity of other muscles unless you reduce the distance between the two electrodes. Otherwise, you would not really know what you are measuring.
This is very doable. Facial muscles provide a very strong signal. But the sensor design is complex. I and another engineer developed a differential sensor easily picks up the signal. Sensor design is obviously very important. Moreover, isolation from any 60 Hz frame ground is essential.
Dear Cari-Iene Mul, I'm sorry but I don't know the acticap EEG equipment (Brainproducts GmbH) and presumably you are trying to adapt an ASC (Analog Signal Conditioning) apparatus, normally used for EEG recordings, to your experimental purposes. Please, don't forget to take care to the fact that EEG and EMG have many different characteristics (e.g., dynamical range, frequency band range, frequency occupation, intensities, etc etc), Anyway, concerning the bipolar EMG positioning for facial recordings I think that 2 cm is a large distance and you risk, besides crosstalk problems, that you will differentiate two signals coming from two different muscles.
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