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P300 speller unusual behavior

Posted: 09 Dec 2014, 00:00
by sunny
Hi all,

i have started working on bci2000 recently, i have been trying to work with p300 speller module with emotiv headset. i am using p300 classifier provided with the bci2000 package. my query is regarding generating output letters from p300 speller.

why does it give wrong output alphabets that i have not concentrated, moreover when i am not concentrating on any alphabets it gives me output in that condition as well. i have set "EpochsToAverage" to 0 but then it does not gives any output.


Re: P300 speller unusual behavior

Posted: 09 Dec 2014, 09:33
by boulay
Hi Sunny,

The default P300 Speller paradigm will ALWAYS make a selection at the end of a trial. For this to work, the user must be attending a target, the EEG recording quality must be good, there must be a discernible difference between target and non-target responses in the averaged EEG signal. If any of these criteria are not true then the P300 speller will not make accurate selections.

There are different things you can do to the application and signal processing so that the system does not make a selection until it is confident that it is making the correct selection (mostly based on the quality of the data), but that is not the default mode of action. Also, when the system is designed to work like this, sometimes it will never be sufficiently confident, even when everything is setup correctly, maybe because there is some noise that doesn't affect the classification but does affect the confidence measure. In other words, it's not always a good idea to use this confidence criterion.

There is a whole literature devoted to P300 signal processing and optimizing P300 speller applications. There are plenty of 'pretty good' solutions, but no guaranteed 100% works for everybody solutions.