famılıar / unfamılıar eeg data

The commercial Emotiv EPOC wireless EEG headset with 14 channels was utilized to capture the associated brain activity during the period of the experiments. The device headset contains AF3, AF4, F3, F4, F7, F8, FC5, FC6, P7, P8, T7, T8, O1, and O2 electrodes of standard and extended 10/20 electrode placement system. It should be noted that central electrodes are missing in the headset. EEG was acquired from these electrode locations and electrode type was Ag/AgCl. The P3 and P4 channels were employed as CMS (Common Mode Sense) and DRL (Driven Right Leg) references, respectively. EEG was recorded at a 128 Hz sampling frequency rate with the help of a 16-bit analog to digital converter. As a default, a 50 Hz notch filter was applied to the EEG recorded from device. After the EEG data was acquired for 14 subjects, all data were examined visually to identify any corrupted records.

Next, all data were primarily pre-processed. In this process, a first order 0.16 Hz digital high-pass Butterworth IIR filter was applied in a forward direction to eliminate the baseline of the data. And subsequently, to remove the background signal (noise) from the EEG, a linear phase low-pass digital FIR filter was used. The order of the filter was chosen as 10 and the bandwidth was determined to be 32 Hz, which is assumed to contain most of the energy of the EEG. The “butter” and “fir1” functions of MATLAB® software were implemented to design the high-pass and low-pass filters, respectively. Lastly each trial of the data was normalized by subtracting its mean and scaling with its standard deviation.

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