Contents
Thought Controlled Devices
What does the system do?
It is a system which acts as an interface between our brain and the task we want to accomplish. It reads our brain, tries to understand what it is thinking about and performs the task.Under this section we will sequentially look at
• input to the system
• processing of the input information
• output of the system
INPUT:
As discussed above, the input to the system are brain waves. Now the question is how we read brain waves. We use a device called EEG (electro encephalo graph) machine to record the activity of brain. This was brought into use about 60 years back and we have developed much advanced devices, but still EEG continues to be the most useful technique. Electrodes are placed in a conventional way on the head. Their number can be as high as hundred. These sensitive electrodes record the minute voltage developed across a neuron and plot the brain waves. But these waves are overlap of several waves with different frequencies and as discussed above, we need to analyze them under different categories to get some meaning out of them.
Fig: EEG pattern of a person under observation
In the next sub section we see how our system can get something meaningful out of this crude input given to it.
PROCESSING
1) Amplification –The signal obtained are very low in magnitude. Small disturbance can cause a large deviation, so the brain waves are amplified.2) Fourier transform –The signal obtained is transformed to frequency domain which helps in further filtering and analysis of the signal.
Fig: Fourier transform of a brain wave -frequencies between 8-13 hz can be seen to dominate, which correspond to alpha waves.
3)Filtering –We are interested only in waves of frequency less than 50 hz. So we filter the Fourier transform of the signal with 50 hz low pass filter.
4) Separation into different components – As seen before, brain waves comprise four categories of waves. We are basically interested only in alpha and beta waves. We now need to break the signal into its components which are waves with frequencies in a particular band. So we pass the signal through two band pass filters
• 8 to 13 hz band pass filter for alpha waves
• 15 to 25 hz band pass filter for beta waves
5) Further filtering –The beta wave Fourier transform is further filtered to get waves more specifically related to some stimuli. This is a difficult process, because it is difficult to identify the frequency related to the stimuli.
6) Inverse Fourier transform –The signals are brought back into time domain because two signals can be properly compared in time domain.
A data base of response of brain towards different stimuli is obtained. Special purpose computers are used to compare signals obtained after processing response towards an arbitrary stimulus with the signals in the data base.
OUTPUT
The system as an output executes the task according to the interpretation of brain waves.
