A definite selection of the electrode positions has been made. IMEC hardware now allows for transmission of up to 8 channels simultaneously. Electrodes for the following positions will be provided in the headset: FP1, FP2, F7, F8, C3, C4, O1 and O2. Almost all of these electrodes can be integrated into the headband section of the headset, only C3 and C4 will be mounted on top of an arm extending to the upper half of the head. Ground and reference electrodes are placed just behind the ears. It is not entirely clear if we are going to need all of the eight available channels. Work has centred upon finding electrode positions which deliver the most efficient data, e.g. in respect with the relationships between pairs, or because of the robustness of the signal. Lowpass filters remove the airborne and omnipresent 50 Hz hum from electrical mains and other background noise that interferes with the reading of microvoltages on the scalp. Signal processing algorithms are written to treat the raw data and return scaled events to the Max/MSP computer which controls the pins on the steel segments.
Soon we will start analysing the brainwave content of these areas in order to map significant data into a format that is meaningful for the distribution of sound.
The international 10-20 system is based upon a division of the head from nasion (the point between the eyes on top of the nose) over cranium (top of scalp) to inion (the bump on the lower rear part of the skull). The “10-20” refers to the percentages that delimit the electrode positions on this line that traverses the scalp.
Here is a more graphic representation: