Not clear on what the autocorrelation function of raw EEG means physically
why can't you take the FT of a the EEG itself and get frequency data?
With BCI & basic electrode setups you can understand your brain activity: neuron-firing --> EEG voltage reading --> brainwave readings
How I understand that this is done:
Fourier Transform: Operation bringing you from TIME domain to FREQUENCY domain
- Time Domain: EEG raw ... x= time , y= volts
- Frequency Domain: brainwave data... x= frequency, y=intensity
Fourier Theorem ... basically that every line/wave can be broken down into pure components (single frequency sinusoids)
First you need the autocorrelation of the raw EEG
- Correlate EEG signal with itself - compare EEG signal at one time pt -- to another time pt... shifted tau
- Get the nature of the EEG signal through time ... how voltages are shifting
FT of Autocorrelation --> PSD We treat the signal as stationary, even though in reality it is moving in time and apply a windowing method like the Welch's Method .. and slide this window along the entire EEG signal.
Outcome is a PSD plot <-- which gives intensity of each frequency band