Abstract — There are a number of people in the world who suffer from disabilities which prevent them from being able to use traditional means to control a computer. For these people, alternate forms of input are required. One potential input device is an Electroencephalography machine which can be used to detect patterns of brain activity and use these patterns to trigger events on a computer such as mouse clicks or keyboard presses. This allows those without the use of their hands to be able to control a computer without invasive surgery.
Electroencephalography or EEG is a technique which uses electrodes to detect and amplify the electrical potential which corresponds to the firing of neurons in the brain. Although each neuron produces its own signal when it fires, it is nearly impossible to detect the activity of a single neuron via EEG. Instead, the firing of thousands of neurons in a pattern produce a signal which is strong enough to be picked up via electrodes placed on the scalp. These patterns can be used to analyse and diagnose mental conditions such as epilepsy, to monitor and observe brain responses to external stimuli, or as a potential means of hands-free control over a system.
Fig. 1 One Second of EEG Signal 
Clinical Electroencephalograph devices use a particular electrode placement known as ‘The International 10-20 System for Placing Electrodes’, or simply the 10-20 system. This method was developed in order to standardize the placement of electrodes on the scalp so that studies could be reproduced easily. The name comes from the fact that the distance between electrodes is either 10% or 20% away from each other. The layout of the 10-20 system is shown in Figure 1.
Fig. 2 The 10-20 International System for placing electrodes 
EEG signals are typically described in terms of (1) rhythmic activity and (2) transients . The rhythmic activity consists of periodic waves of a particular frequency. Most EEG signals fall in between the ranges of 1Hz and 30Hz. These frequencies are broken down into specific bands, each of which pertains to a specific segment of mental activity.
Type Frequency Range (Hz) Normally
Delta 1Hz – 4Hz Slow wave sleep
Theta 4Hz – 7Hz Drowsiness
Alpha 8Hz – 12Hz Relaxation
Beta 12Hz – 30Hz Concentration
Fig. 3 Comparison of EEG Bands 
Rhythmic EEG activity consists of the standard electrical activity being generated by the brain. Peak activity generally falls into one of the four spectrum bands as listed above. For example, when the user is relaxed, there will be a peak of activity somewhere in between 8Hz and 12Hz. This makes it possible to determine when a person is relaxed or when they are concentrating based on the primary frequency in the signal.
Transient activity on an EEG is activity which is caused by temporary events such as seizures. Muscle movement such as the blinking of an eye, or the movement of facial muscles can also produce temporary...