P300 and EMOTIV EPOC: Does EMOTIV EPOC capture real EEG?
P300 (or P3) is one of the components in an ERP waveform (Illustration 2). It is a positive deflection in voltage (2-5μV) with a latency of about 300-600 ms from the stimulus onset. It is typically measured by placing electrodes covering the regions Fz, Cz and Pz (Illustration 1). Since the strength of an ERP signal is a very low it is usually hidden within the noise and not visible in a typical EEG recording. Therefore, to see the actual ERP waveform one has to bandpass filter the EEG signals (typically 1-20 Hz) and averaged over multiple trials (calls epochs, usually segments of -1000 ms and 2000 ms relative to each stimulus). The most popular experiment for obtaining P300 is called P300-speller (Illustration 3), which is a 6×6 matrix of alphanumeric characters where one of its rows or columns flashes randomly at a time in a sequence (also calls the odd-ball paradigm) while the subject is focusing on one of the characters in the matrix. Whenever the subject sees that the cell containing the character he/she is focusing flashes, the subject has to count the number of times that cell has flashed. After the experiment, the averaged epochs containing targets (flashings of focused cells) is compared against averaged epochs containing non-targets (other background flashes). What one would see is that average signal for epochs of targets forms an ERP waveform while for non-target epochs forms some kind of a random signal. However, random artifacts, such as from eye movements, within EEG recordings significantly distort the resulting ERP waveform.