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Hi all,

I wonder if there is a way to sent the selected target to P3 speller directly instead of sending stimulusCodeRes and Classification score (signal processing module is fieldtrip buffer, matlab). We want to implement our own decision making part. Also, I need the P3 speller to stop and begin next trial immediately after received the selected target for realizing a dynamic stop strategy. Thank you very much.

Yichuan

Hi Yichuan,

this is not possible with an unmodified version of the P3Speller. Also, it does not make too much sense IMHO because signal processing code only sees StimulusCodes, which are associated with _groups_ of targets (rows and columns) rather than targets themselves. Only the P3Speller knows how targets relate to StimulusCodes, so your signal processing code cannot determine the selected target.

However, you can encode a selection by transmitting a pseudo classification score which is 1 for each row or column which contains the desired target, and which is 0 for each row or column that does not contain the desired target.

Also, I need the P3 speller to stop and begin next trial immediately after received the selected target for realizing a dynamic stop strategy.

For a dynamic stop strategy, you will need to modify the P3Speller source code. To end a sequence, it must return two 0s in sequence from its OnNextStimulusCode() function.

Regards,
Juergen

Dear Jeurgen,

Thanks for your response to the previous person. I am stuck in the same situation. I want to do the classification in my fieldtrip signal processing.
Can you indicate me how to "encode a selection by transmitting a pseudo classification score which is 1 for each row or column which contains the desired target, and which is 0 for each row or column that does not contain the desired target" ?

Thanks for your time,
Alireza

Hi Alireza,

there is a parallel thread which discusses how to send likelihood values to the P300 speller through the FieldTripBuffer:
http://www.bci2000.org/phpbb/viewtopic.php?f=4&t=1281

Let me know if you need additional information.

Regards,
Juergen