Artifacts detection is achieved by the Riemann Potato box. Signal is first epoched into 2 s epochs at an interval of 100ms. This epoched signal is then used by the potato box.
The Riemann potato box is adaptive, and start training when the stimulation OVTK_StimulationId_ExperimentStart is received. After 5 seconds, the potato start to be effective, and a stimulation OVTK_GDF_Incorrect is sent a the beginning of each artefact. A stimulation OVTK_GDF_Correct is sent when the artefact end. The potato box has 2 important parameters, Speed of adaptation (by default 100), by increasing this value, the adaptation will be slower, and Threshold (by default 2.5, corresponding to the number of standard deviation from the mean), by increasing this value, the potato will be less sensitive to small artifacts.
Communication with the P300 application is done through a VRPN button server. This server has 3 buttons :
- Button 1 : Start Stimulation. ON when openvibe start. this is usefull when the P300 application is configured to start openvibe.
- Button 2 : Artifacts stimulation. ON when an artefact begins, OFF when an artefact ends.
- Button 3 : Training Completed Stimulation. ON when training is completed. This is usefull when the P300 application is configured to stop openvibe.