Synchronisation Issues in Wireless EEG Systems for P300 Amplitude Measurement: Ab Medica Helmate Case Study.

New wireless devices allow EEG acquisition during walking and support the investigation on the relationship between cognition and movement. In particular, P300 is a positive deflection in the EEG signal occurring approximately 300 ms after a stimulus recognition. P300 is demonstrated to be useful in the detection of cognitive state and in the diagnosis of several neurodegenerative disorders. P300 is a very low amplitude signal and it is detectable by averaging over several EEG trials (assuming zero mean noise). Wireless data transmission may suffer latencies due to the wireless protocol, introducing synchronisation uncertainty between stimulus occurrence and marker apposition on EEG signal. This uncertainty propagates through the averaging operation in P300 computation. Consequently, the amplitude measurement of the P300 is affected. The aim of this study is to implement an uncertainty propagation analysis by means of Monte Carlo simulation in order to test wireless EEG metrological performances in P300 measurement. 56 ms of uncertainly synchronization (98 % confidence interval) resulted in negligible uncertainly on P300 amplitude measurement for clinical applications.