I would like to introduce you a brain signal that I think is very special, called P300.
First of all, let’s talk about what the P of P300 means. P in P300 means positive, simple, so we can expect that the P300 will have a large positive signal.
Conversely, if one starts with N, N stands for negative, and we would expect to see a negative signal.
What is 300, then? It means 300 microseconds
So P300 simply means a positive signal detected in the brain 300 microseconds after the stimulation
If it is N400, then it is a negative signal that will be detected 400 microseconds after the stimulation
Sometimes it will be simplified to a P3 signal. It is the same, people are just lazy because most signals will be rounded to hundreds of integers. I rarely see N170 or something like that, but there seem to be some special cases that have it.
Mechanism of P300
In terms of mechanism, let’s talk about the stimulation for P300. The previous SSVEP uses visual stimulation, and the P300 can receive many types of stimulation. It can be visual or auditory, but there must be a feature that it has to be an UNEXPECTED signal.
It sounds sketchy, but let me give you an example.
Let’s keep playing Do Re Mi Fa Sol’s Do sound. Keep playing it, and then suddenly we switch to Mi, such a sudden change will generate a signal in the brain after 300 microseconds.
The pattern has to be random, for example, Do Do Do Mi Do Do Mi Do Do Do Do Mi. As you can see Mi appears randomly in the sequence.
Visual stimulations can also be used. For example, we keep putting the same picture, suddenly change to another person, and then change back, The change will create a positive signal 300 microseconds later in the prefrontal and parietal lobes.
By Gray, vectorized by Mysid, colourd by was_a_bee. - File:Gray726.svg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=8880888
Or we can show a board to the subject where the board is pre-designed. The subject stares at one of the characters on the board, and the character will light up in random order, and when the one subject is staring at suddenly lights up. There will also be a signal in their brain, and we can go back 300 microseconds to see which character the subject was watching.
Advantage of P300
Multiple types of stimuli can be used
Even if people are watching something else, auditory stimulation can be used.
Disadvantage of P300
Low autonomy
Because the signal has to be predesigned, nothing can be manipulated if it is not written in the software.
Not Real-Time
Because it has to be unexpected, we have to make people get used to some patterns first. Although it may not take long for people to get used to something, it still takes a couple of seconds to do it. After that, 300 microseconds are needed for the signal to be detected. It’s basically impossible to be a real-time technology.
My Point of View
P300 is a very interesting signal, especially the way it is created, which is unexpected events, However, I personally think that this signal is difficult to use as a BCI application, although it is very similar to SSVEP, which can be used with visual stimulations, its delay makes its application be limited. But it’s hard to say, maybe while reading this article, you may be able to come up with some interesting applications to commercialize it. Don’t forget to tell me about it!
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