18-03-2011, 10:59 AM
Presented by:
K.L.V. Mahesh Babu
[attachment=10466]
INTRODUCTION:
Today the use of computers is extended to every field.
Many sophisticated devices like touch screen, track ball, digitizers etc made interaction with computer ease from novice to professional.
But physically disabled individuals are deterred from using computers due to their inability to control mouse. However, if directional discrimination of an icon can be achieved, quadriplegics can take the function of a mouse without the use of hand.
→ Computer is used in every field now. Mice and touch screens are a nice improvement over keyboard for some tasks but it can’t be useful for quadriplegics.
→ Although several hardware and software interfaces have been devised for the handicapped computer user, there are no inexpensive systems that deliver the true power and ease of today's computers.
→ This encompasses the construction of the eye-tracking hardware and its fine-tuning in software.
ELECTRO-OCULOGRAPHY:
→ One eye-tracking method in which blink (and in fact all eye movement) data is particularly simple to collect and analyze, even with very modest equipment, is electro-Oculography.
→ Through the six extra-ocular muscles by, Absolute eye position Speed Direction of movement, or through the levanter palpebrae (eyelid) and other peri orbital muscles as unilateral or bilateral blinking and blink duration.
→ Higher metabolic rate at retina maintains a voltage of +0.40 to +1.0. This cornea-retinal potential is measured by surface electrodes placed on the skin around the eyes. The actual recorded potentials are smaller, in the range of 15 to 200 micro volts, and are usually amplified before processing event.
→ The potential across two electrodes placed posterior laterally to the outer acanthi is measured relative to a ground lead strapped around the wrist or clipped to the auricle, and the resulting voltage amplified and sent though a custom-built, 8-bit analog to digital converter filtered to remove high-frequency electrical noise.
→ The converter fits into an IBM PC expansion slot, and transmits the digitized data through the PC serial port to a SUN workstation for display.
DESIGN CONSIDERATIONS:
Eye muscles cannot be operated directly as that of muscles present in the foot and hand. Hands are only the extension of the eye i.e., they select the computer screen as selected by the look. So if we delete the intermediate steps & if we directly control by look it is helpful for both handicapped & non handicapped
ELECTRO-OCULOGRAPHY:
→ EOG is based on electrical measurement of the potential difference between the cornea and the retina. This is about 1 mv under normal circumstances.
→ The Cornea-retinal potential creates an electrical field in the front of the head. This field changes in orientation as the eyeballs rotate. The electrical changes can be detected by electrodes placed near the eyes.
→ The two eyes move in conjunction in the vertical direction. Hence it is sufficient to measure the vertical motion of only one eye together with the horizontal motion of both eyes. This gives rise to the three channel recording .
→ Our eyes need to move in order to keep the image of whatever we are interested in at the central part (called the fovea) of the retina. The saccadic movement is used to "jump" from one object of interest to another.
→ The orientation of the eyes is measured by triangulation.
→ The accuracy of the location determination depends on the accuracy with which the eye orientation is determined.
SYSTEM DESIGN:
→ The hardware part of the system is fairly straightforward.
Our overall design philosophy has been to keep the actual add-on hardware (i.e., in addition to the computing hardware) as simple as possible.
→ The actual hardware fabricated amplifies the voltage picked up by the transducer, removes the electrical line frequency and removes high frequency noise (120 Hz low pass stage).
→ Subsequently, the analog signal is converted to digital form and the data samples are sorted in an IBM PC and finally transferred to a UNIX based workstation, where all the software processing will take place.
Interaction of the System with User:
The graphics displays in these two modes are
1. In the synchronizing mode, the system displays a moving cursor and the user is asked to follow the cursor. The cursor follows a fixed path and the user's eye movements are analyzed to verify that the pattern of movement and the cursor motion is the same
2. The second interaction mode is the command mode, where the cursor is moved by the system to track the user's gaze. The cursor is at the center of display .
→ When the user looks at the start button the cursor follows his or her gaze. Then the command is activated by the user winking twice - i.e., the machine is started. The natural blink & valid blink must be distinguished.
Removal of Noise:
1. Signal smoothing and filtering to eliminate noise. Calculation of quantitative parameters from the signal channels (two for horizontal movements, one for each eye, and one for vertical movement of the eyes). These parameters are angular positions, angular velocities, and angular accelerations of the eyes.
2. Extraction of symbolic tokens from the signal. These tokens indicate the directions of the movement of the gaze (e.g.: North, south).
Possible near future improvement:
→ The first and most important change needed by the above described system is a new board. The experimental board contributes to wrong box selection due to erroneous signals resulting from wire wrapping.
→ A new board which is being designed now will have better isolation and more importantly four channels (two per eye) instead of two. This will enable the software performance improvement, as well as some additional features which will be added (e.g. processing of a one eyed wink).
→ Also needed is a better input device. Attaching electrodes to the skin one by one is cumbersome and annoying for the user. What we need is some device which can be put on by the user himself with ease.
CONCLUSION:
→ There are many ways to measure eye movement, some far more accurate than EOG, but these are expensive.
→ Furthermore, the eye tracking method is just a means, one in which pinpoint accuracy is not really necessary; the provided service and ease of use of the eye-controlled interface is the true goal.
→ This is further under work to resolve the current faults and weaknesses, and implement the eye-tracking device in the most user friendly and efficient interface we can devise.
???
