My experiment is regarding showing some visual stimulus to people while recording the EEG. The stimulus is of 3 types. One is facial recognition and other two is a simple one: Showing an object moving around. I want to extract the different ERP components from this experiment. I have BioRadio EEG device. It can record the voltages value.
I understand that ERP data requires performing an experiment by averaging it 30-50 times. How is this averaging done ? How do I extract the ERP components from the averaged value ? Please any help would be very helpful.
Useful in clinical applications are indeed the average Evoked Reponses (EPs). Averaging is necessary because individual EPs vary significantly. Unfortunately, even the average EPs vary in amplitude and latency between subjects and of course in function of the visual stimulus tested . My opinion is that they must be always treated statistically.
You may find the following introductory texts instructive:
Luck, S. J. (2014). An introduction to the event-related potential technique. MIT press.
Handy, T. C. (Ed.). (2005). Event-related potentials: A methods handbook. MIT press.
Definitely read up on how it's done and what it even means to find a certain ERP. It's not so straight-forward and no software would show you a P3, or any other component, as such. Each component is identified based on its polarity (positive, negative), topography (where on the skull is the activation (of a certain polarity) detected), and latency (when (after the stimulus onset) is the activation visible). Identifying a component requires some experience in the first place. It also requires the researcher to be very much informed on what kind of ERPs they can expect in a certain experiment. P3, for example, can be confused with LPP. N200 may become N170 when presenting faces.
Make sure you inform yourself in the literature before you claim a certain wave is an ERP. Luck is definitely a brilliant source for getting well-informed.
Good luck! :)
Hello,
How is this averaging done?
You need to tag the EEG with the exact onset of the stimuli on screen.
This may be achieved using the trigger channel of your amplifier.
Then, you extract an epoch of signal after each tag. The duration of this epoch may vary according to the ERP you are looking for. One second should be enough to record visual ERPs. Finally, arithmetically average together the epochs with the same type. Softwares as OpenVibe may help you with this process.
[1] A. Andreev, A. Barachant, F. Lotte, and M. Congedo, Recreational Applications of OpenViBE: Brain Invaders and Use-the-Force, vol. chap. 14. John Wiley ; Sons, 2016.
You may want also use some millisecond accurate triggering ...https://www.braintrends.it/devices.html
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