I have an Emotiv EPOC (EEG headset: 128 SPS, notch filter @60 Hz, felt saline contacts) I've been playing around with. Over the course of two or three hours using CCA to plot an SNR contour against frequency and time over O1, O2, P7, and P8, I noticed that a strong background signal in the alpha-wave range was existent at ~10 Hz, but then after a while of doing other things and coming back to it the strong background signal at 10 Hz disappeared but a strong background signal at a smidgen over 8 Hz was present instead.
Naturally, this leads me to ask the question: what the heck is going on? Unfortunately, that doesn't make for a good stackexchange question title, so the replacement question:
Can alpha wave frequencies vary within a single subject over the course of a single day? If they can, by how much, and under what conditions?
(if they can't, I have to start figuring out what the heck caused those artifacts...)