P300 speller flashing

[faisal-awan]

Hi

I want to know that how the P300 speller (BCI2000)flashing was setup ? mean as i know it should be in the blocked randomized form i,e ; one complete cycle of 12 flashes , with every time one row or column flashes. am i right? if not please correct me here.

If for example we dont make the speller in the above mentioned fashion , what will be the effect or drawback ? . mean if i have block of 12 flashes with maybe any row get 3 time flashes or 2 time flahes at a time or may be in different times within 12 that 12 flashes .

hope u understand the Question.

[mellinger]

I want to know that how the P300 speller (BCI2000)flashing was setup ? mean as i know it should be in the blocked randomized form i,e ; one complete cycle of 12 flashes , with every time one row or column flashes. am i right? if not please correct me here.

You are right, flashing is block randomized.

If for example we dont make the speller in the above mentioned fashion , what will be the effect or drawback ? . mean if i have block of 12 flashes with maybe any row get 3 time flashes or 2 time flahes at a time or may be in different times within 12 that 12 flashes .

As far as I know, no one tried removing block randomization from the P3 speller. You might try and check out whether classification gets worse if you don't use block randomization.

You can do this in BCI2000 by modifying src/core/Application/P3Speller/P3SpellerTask.cpp, function P3SpellerTask::OnNextStimulusCode(). Rather than re-using the same sequence over and over, use a single sequence that is longer and contains all repetitions in a shuffled fashion.

Juergen