bci2000.org BBS

In Stimulus Presentation If I have a stimulus that occurs two times in the same sequence do those two stimuli get averaged by the P3TemporalFilter together or not?

An example is:
Application Parameters:
SequenceType: deterministic
Sequence: 1 1 2
No of Sequences: 1

Does the P3Temporal Filter average the 2 occurances of Stimulus 1 together? or not?

In its current form, the P3TemporalFilter will accumulate data until NumberOfEpochs presentations have occurred for a stimulus, and will then output the average waveform, such that StimulusPresentation can pick up the classification value for that stimulus. Then, P3TemporalFilter will ignore data for that stimulus, until it has occurred NumberOfEpochs times in total.

Thus, when you present a stimulus multiple times during a sequence, P3TemporalFilter will go out of sync with stimulus presentation. In the Sequence parameter, specify each stimulus once, or not at all.

To allow for classification of stimuli with a variable number of presentations, averaging over stimuli would need to occur in application modules rather than the signal processing module, as is currently the case in BCI2000. It might be possible in future versions of BCI2000, though.

Regards,
Juergen