Odd Visual P300 morphology
Posted: Fri Jun 09, 2006 5:03 pm
We recorded a couple people with our new 168 channel ActiveTwo, Mark II system. We are executing data pre-processing in BESA 5.1.6. Our P300 paradigms are very simple and have elicited strong and reliable visual and auditory oddball responses in the past.
However, with this system, when the ERPs are averaged in BESA, we end up with what appears to be an extension of the baseline for about 100ms past the trigger event around which we are epoching, in all visual conditions only, across all channels.
This effect is persistent across other visual stimulus paradigms we have piloted with the system, including a Posner-style cueing task, a scene analysis task, and an IOR task. Data files opened in BESA, either collected from different systems or manually generated, do not demonstrate this phenomenon.
We have extensively tested trigger:stimulus variability comparative analysis of our Biosemi data against an oscilloscope and have found there to be a variation of no more than +/-1ms at our 2048Hz sampling rate. We collect data in a new Lindgren EM shielded enclosure, which has demonstrated strong attenuation of noise. We have also verified all of our electrode locations between our cap and the BESA montage.
We are at a loss for why our Biosemi data shows the extended baseline effect across visual paradigms, but not auditory.
Do you have any suggestions as to why the data would be treated differently, as to why the effect is occurring, and as to how we can continue troubleshooting it?
We're going to also begin coordinating with Cortech Solutions and BESA Support for assitance.
Thanks,
Jake
However, with this system, when the ERPs are averaged in BESA, we end up with what appears to be an extension of the baseline for about 100ms past the trigger event around which we are epoching, in all visual conditions only, across all channels.
This effect is persistent across other visual stimulus paradigms we have piloted with the system, including a Posner-style cueing task, a scene analysis task, and an IOR task. Data files opened in BESA, either collected from different systems or manually generated, do not demonstrate this phenomenon.
We have extensively tested trigger:stimulus variability comparative analysis of our Biosemi data against an oscilloscope and have found there to be a variation of no more than +/-1ms at our 2048Hz sampling rate. We collect data in a new Lindgren EM shielded enclosure, which has demonstrated strong attenuation of noise. We have also verified all of our electrode locations between our cap and the BESA montage.
We are at a loss for why our Biosemi data shows the extended baseline effect across visual paradigms, but not auditory.
Do you have any suggestions as to why the data would be treated differently, as to why the effect is occurring, and as to how we can continue troubleshooting it?
We're going to also begin coordinating with Cortech Solutions and BESA Support for assitance.
Thanks,
Jake