## A question about the “Epoch averaging” in BCI P300

About Brain Computer Interfaces, EEG, neurofeedback, related event announcements, jobs, etc.
etc
Posts: 23
Joined: Sat Mar 07, 2020 4:33 pm

### A question about the “Epoch averaging” in BCI P300

A question about the “Epoch averaging” in BCI P300. Sorry for my bad English!
I suppose:
1) 250 hz, then I have a sample every 4 ms.;
2) 4 channels;
3) in “Stimulation based epoching” I set 0-0,4;
4) then, I have this matrix output from “Stimulation based epoching”:
time0 ch1, time0 ch2, time0 ch3, time0 ch4
time0.004 ch1, time0.004 ch2, time 0.004 ch3, time 0.004 ch4
……….

……….
time0.40 ch1, time0.40 ch2, time0.40 ch3, time0.40 ch4

The question is:
if I put the box “epoch average” after the box “Stimulation based epoching”, the averages on what elements are computed?
1) The average is only for column (i.e. for channel), only for row (i.e.for the time) or other?
2) The average is only inside one epoch (what I produced with Stimultaion based epoching, alias the signals from 0 to 0,4 after the stimulation) or also between more epochs?
Thank you very much.
Etc

Thibaut
Posts: 230
Joined: Wed Oct 31, 2018 9:14 am

### Re: A question about the “Epoch averaging” in BCI P300

Hi,
1) 250Hz is 250 per seconds so 4ms is right.
3) I don't understand your parameter... Epoch average is here to set an epoch and an epoch with a time of 0 is not an epoch it's a classical sample, so you take only the sample by channel after 0.4s of your stimulation.
If you wan't to take all the 0.4s after stimulation your parameter need be to invert.
The epoch average make the average of samples in the epochs so if you have 4 channels and your epoch here contain only one sample so the average epoch make nothing.

Thibaut

PS : 4ms is 0.004s not 0.4s

etc
Posts: 23
Joined: Sat Mar 07, 2020 4:33 pm

Dear Thibaut,