Preprocessing EEG & MEG final

Pre-processing

for EEG and MEG

Przemek Tomalski

&

Kathrin Cohen Kadosh

Recording EEG

QuickTime™ and a

TIFF (Uncompressed) decompressor

are needed to see this picture.

Two crucial steps

 Activity caused by your stimulus (ERP) is

‘hidden’ within continuous EEG stream

 ERP is your ‘signal’, all else in EEG is ‘noise’

 Event-related activity should not be random, we

assume all else is

 Epoching – cutting the data into chunks referenced

to stimulus presentation

 Averaging – calculating the mean value for each

time-point across all epochs

Extracting ERP from EEG

ERPs

emerge from

EEG as you

average

trials

together