Before revision:  Electroencephalograms (EEGs)used in BCIs are weak, easily contaminated by interference and noise , non-stationary for the same subject, and varying across different subjects and sessions .
After revision:  Electroencephalograms (EEGs)used in BCIs are weak, easily contaminated by interference and noise , is sensitive to noise/artifact and suffers between-subject/within-subject non-stationarity .