I’ve noted from your EEG examples on ICA that blinks show up always as positive deflections, while in some data I’m testing blinks are showing as negative deflections (as in the screenshot below).
QUESTIONS
Would you suggest me to invert the polarity (e.g. multiplying each sample by -1) to display the signal as you do, or does not matter at all ?
In general, looking at the filtered raw signal in the screenshot (4 seconds rec), at first glance does it look a nice or bad EEG recording? Just curious about your expert opinion on this,
polarity of blink deflections does not matter, no need to invert.
At a glance it looks like a normal EEG recording, not bad (though I’m guessing a bit because there is no time scale; I’m inferring the time scale based on the length of the blinks).
To explain a bit more, it depends on the hardware used to record the EEG. Each channel on an EEG measures the difference in potential between 2 points, the electrode and the reference. Some amplifiers return electrode - reference, while others return reference - electrode. As you can see, the polarity does not matter since it is the same for all channels of a given amplifier.
However, when working on ERP studies, some people like to have the known responses always in the same polarity. For instance, in auditory oddball, the convention is to have the N1 positive and the P3 negative (IIRC, which I am now doubting since N=Negative and P=Positive?).
