1. INTRODUCTION:

Man machine interface has been one of the growing fields of research and development in recent years. Most of the effort has been dedicated to the design of user-friendly or ergonomic systems by means of innovative interfaces such as voice recognition, virtual reality. A direct brain-computer interface would add a new dimension to man-machine interaction. A brain-computer interface, sometimes called a direct neural interface or a brain machine interface, is a direct communication pathway between a human or animal brain(or brain cell culture) and an external device. In one BCIs , computers either accept commands from the brain or send signals to it but not both. Two way BCIs will allow brains and external devices to exchange information in both directions but have yet to be successfully implanted in animals or humans. Brain-Computer interface is a staple of science fiction writing. In its earliest incarnations no mechanism was thought necessary, as the technology seemed so far fetched that no explanation was likely. As more became known about the brain however, the possibility has become more real and the science fiction more technically sophisticated. Recently, the cyberpunk movement has adopted the idea of 'jacking in', sliding 'biosoft' chips into slots implanted in the skull(Gibson,W.1984).Although such biosofts are still science fiction, there have been several recent steps toward interfacing the brain and computers. In this definition, the word brain means the brain or nervous system of an organic life form rather than the mind. Computer means any processing or computational device, from simple circuits to silicon chips (including hypothetical future technologies like quantum computing). Research on BCIs has been going on for more than 30 years but from the mid 1990s there has been dramatic increase working experimental implants. The common thread throughout the research is the remarkable cortical-plasticity of the brain, which often adapts to BCIs treating prostheses controlled by implants and natural limbs. With recent advances in technology and knowledge, pioneering researches could now conceivably attempt to produce BCIs that augment human functions rather than simply restoring them, previously only the realm of science fiction.

Fig. 1 Schematic diagram of a BCI system

Brain Computer interface (BCI) is a communication system that recognized users command only from his or her brainwaves and reacts according to them. For this purpose PC and subject is trained. Simple task can consist of desired motion of an arrow displayed on the screen only through subject's imaginary of something (e.g. motion of his or her left or right hand). As the consequence of imaging process, certain characteristics of the brainwaves are raised and can be used for user's command recognition, e.g. motor mu waves (brain waves of alpha range frequency associated with physical movements or intention to move).

An Electroencephalogram based Brain-Computer-Interface (BCI) provides a new communication channel between the human brain and a computer. Patients who suffer from severe motor impairments (late stage of Amyotrophic Lateral Sclerosis (ALS), severe cerebral palsy, head trauma and spinal injuries) may use such a BCI system as an alternative form of communication by mental activity.

The use of EEG signals as a vector of communication between men and machines represents one of the current challenges in signal theory research. The principal element of such a communication system, more known as Brain Computer Interface, is the interpretation of the EEG signals related to the characteristic parameters of brain electrical activity.

The role of signal processing is crucial in the development of a real-time Brain Computer Interface. Until recently, several improvements have been made in this area, but none of them have been successful enough to use them in a real system. The goal of creating more effective classification algorithms, have focused numerous investigations in the search of new techniques of feature extraction.

The main objective of this project is the establishment of a Time Frequency method, which allows EEG signal classification between two given tasks (geometric figure rotation and mental letter composing), as well as the familiarization with the state of the art in time-frequency and Brain Computer Interface. The extension of this method to a five-task classification problem will be also considered.

BRAIN COMPUTER INTERFACE:

2.1 What is Brain Computer Interface ?

A new brain-computer-interface technology could turn our brains into automatic image-identifying machines that operate faster than human consciousness. DARPA ( Defense Advanced Research Projects Agency) is funding research into the system with hopes of making federal agents' jobs easier. The technology would allow hours of footage to be very quickly processed, so security officers could identify terrorists or other criminals caught on surveillance video much more efficiently. The system harnesses the brain's well-known ability to recognize an image much faster than the person can identify it. Our human visual system is the ultimate visual processor coupling that with computer vision techniques to make searching through large volumes of imagery more efficient. The brain emits a signal as soon as it sees something interesting, and that "aha" signal can be detected by an electroencephalogram, or EEG cap. While users sift through streaming images or video footage, the technology tags the images that elicit a signal, and ranks them in order of the strength of the neural signatures. Afterwards, the user can examine only the information that their brains identified as important, instead of wading through thousands of images. The major weakness of computer vision systems today is their narrow range of purpose,a system that is intended to recognize faces and apply it to recognizing handwriting or identifying whether one object in a photo is behind another. Unlike a computer, which can perform a variety of tasks, a computer vision system is highly customized to the task it is intended to perform. They are limited in their ability to recognize suspicious activities or events. People, on the other hand, excel at spotting them. The new system's advantage lies in combining the strengths of traditional computer vision with human cortical vision. For example, when a computer searches for vehicles, it will identify and discard parts of the image that contain water. The human user, who is more likely to easily spot oddities, can then look only at the parts of the image that matter. This could allow time-sensitive searches to be performed in real time.

As mentioned in the preface a BCI represents a direct interface between the brain and a computer or any other system. BCI is a broad concept and comprehends any communication between the brain and a machine in both directions: effectively opening a completely new communication channel without the use of any peripheral nervous system or muscles.

In principle this communication is thought to be two way. But present day BCI is mainly focusing on communication from the brain to the computer. To communicate in the other direction, inputting information in to the brain, more thorough knowledge is required concerning the functioning of the brain. Certain systems like implantable hearing-devices that convert sound waves to electrical signal which in turn directly stimulate the hearing organ already exist today. These are the first steps. The brain on the other hand is on a whole other complexity level compared to the workings of the inner ear.

From here on the focus is on communication directly from the brain to the computer. Most commonly the electrical activity (fields) generated by the neurons is measured, this measuring technique is known as EEG (Electroencephalography). An EEG-based BCI system measures specific features of the EEG-activity and uses these as control signals.

Over the past 15 years the field of BCI has seen a rapidly increasing development rate and obtained the interest of many research groups all over the world. Currently in BCI-research the main focus is on people with severe motor disabilities. This target group has little (other) means of communication and would be greatly assisted by a system that would allow control by merely thinking.

Fig.2 BCI

2.2 Basic BCI layout:

The concept of thinking is perhaps too broad a concept and can actually better be replaced by generating brain patterns. The general picture of a BCI thus becomes that the subject is actively involved with a task which can be measured and recognized by the BCI. This task consists of the following: evoked attention, spontaneous mental performance or mental imagination. The BCI then converts the command into input control for a device.

This is the basic idea. With the continuously increasing knowledge of the brain and advances in BCI over time, perhaps BCI will be able to extract actual intentions and thoughts. This however does not appear to be on the cards for the very near future.

The Wonder Machine Human Brain:

The reason a BCI works at all is because of the way our brains function. Our brains are filled with neurons, individual nerve cells connected to one another by dendrites and axons. Every time we think, move, feel or remember something, our neurons are at work. That work is carried out by small electric signals that zip from neuron to neuron as fast as 250 mph. The signals are generated by differences in electric potential carried by ions on the membrane of each neuron. Although the paths the signals take are insulated by something called myelin, some of the electric signal escapes. Scientists