I recently conducted an EEG experiment using a passive Oddball paradigm with two experimental conditions : standard stimuli (occurring with a 85% probability) and deviant stimuli (occurring with a 15% probability). This experiment was conducted on 10 participants.
ERP were recorded with 64 electrodes.
An ANOVA test on the prestimulus baseline period yielded a significant effect of the condition. I have observed a difference between standard stimuli's wave and deviant stimuli's wave. There shouldn't be such a difference between these two but I understood that this difference is caused by a smaller number of trials in the deviant condition than in the standard one.
However, I'm still wondering whether this significant difference can be caused by the small number of participants (n=10) or by too small inter-stimulus interval (ISI=1500ms) ? How do you suggest I should deal with this significant baseline regarding the understanding of MMN/P3 effects ?
I looked on cogsci.SE and I didn't find anything relevant to my question.