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EYE INTERFACE TECHNOLOGY ELECTRO OCULOGRAPHY

By:Praveen kumar

cutouteye

Abstract:

               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.  I come before with a new model of based on Electro-Oculography which uses Electro-oculogram Bio potential amplified signal to control  computer .  I introduce a new keyboard design, some modifications in design to overcome the drawbacks in existing model

INTRODUCTION: Computer is used in every field now.  Mice and touch screens are a nice improvement several hardware and software interfaces have over keyboard for some tasks but it can’t be useful for quadriplegics. Although been devised for the handicapped computer user, there are no inexpensive systems that deliver the true power and ease of today's computers. It is estimated 150, 00 severely disabled persons able to control only the muscles of their eyes without any problem. This encompasses the construction of the eye-tracking hardware and its fine-tuning in software. 

 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.  Most eye-tracking systems have chiefly addressed the need to measure eye position and/or movement, treating blinks merely as artifact to be discarded. This would be a serious mistake in a practical interface, as will be discussed later. But fortunately, almost all systems can easily be extended to process blink data.

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. 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. On the positive side, the equipment is cheap, readily available, and can be used with glasses or contact lenses, unlike some reflection methods.

 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: Principles and Practice:     

          EOG is based on electrical measurement of the potential difference between the cornea and the retina. This is about 1 mv under normal circumstances.


    Child with the EOG Electrodes

 

                              

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.

 

 

                                                         

Figure: The child drawn a image using

EOG

It is possible to obtain independent measurements from the two eyes. However, 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 system shown in Figure 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. Thus there are four types of eye movements, called vestibular, opto-kinetic, saccadic, and pursuit. The first two have to do with the largely involuntary head motion.  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.  Some of the noise patterns such


as the 60 Hz line frequency can be easily removed, using a notch filter. Other noise artifacts are by the turning of an electrical switch on/off in the vicinity of the electrodes contraction of the facial or neck muscles   slippage of the electrode due to sweat and eye blinking. Eye blinking is considered noise in ENG. However, the signals produced by eye blinks are, in fact, quite regular. This makes it easy to recognize and eliminate them

Current Eye Track System   :    Our objective in this project was to build a 2D point-of-regard controlled spatial locator system and demonstrate its feasibility in a computer graphics environment.  We acquire data using an IBM compatible PC and perform software development on a SUN workstation. This decision was based on convenience. Hardware prototyping is inexpensive and quick on the PC bus because of the wide availability of components and printed circuit boards available in the market specifically for this purpose.

On the other hand, the window based user interface software (based on Xp windows) is at present better supported on the SUN and other UNIX based workstations. We chose X as our window environment because it is rapidly evolving into an industry standard. In the future, production systems based on our research can easily be wholly resident in the PC, since X products for the PC have already appeared in the market, and we expect such products to dominate window system development within the next few years. The initial work involved hardware directions of the movement of the gaze (e.g.: North, south).


Software Discussion:                                  

          The above discussed software is a 3 x 2 boxed menu driven eye selected interface. This menu has two levels, thus enabling a choice of any letter in the alphabet, as well as some additional punctuation characters. When the program is run, there are several parameters which need to be defined to give the software the ability to make a correct choice (number of calibration repetitions, number of data samples necessary for absolute choice determination, different thresholds, etc.). The above parameters can be set manually, or "automatically", by an auto-calibration mode.

Once the parameters are set, a second calibration mechanism is invoked. The user follows a box which horizontally moves back and forth on the screen, until calibrated. This mechanism is invoked at this experimental stage every time before the software is ready to attempt a menu Selection.. determination

                                 

Thus the finally designed wheel chair for the users is projected behind which helps the handicap persons and quadriplegics.

 

 

 

 

 

 

 

              

 

 

Wheel chair can be controlled using EOG by various guidance strategies:

         1. Direct Access Guidance,

         2. Guidance by automatic or semiautomatic and   Scanning techniques and

         3. Guidance by Eye commands           

                              

Direct access interface.                                                    State machine using speed fixed per event        

The set of possible commands are:

FORWARD: The robot’s linear speed increases (the wheelchair moves forward).

BACKWARD: The robot’s linear speed decreases (the wheelchair moves backward).

RIGHT: The angular speed increases (the wheelchair moves to the right):

LEFT: The angular speed decreases (the wheelchair moves to the left).

DRAWBACK :  The drawback of this interface is the Midas Touch problem: the human eye is always ON and therefore, it is  always looking somewhere. Everywhere the user looks, another command is activated

 

Scanning Guidance :

this system the user accesses the desired command by scanning all the established guidance commands

 

                     

 

 

STOP: The robot stays stopped.

 

Guidance by Eye commands :

                       

 

UP: The wheelchair moves forward.  & Increase in linear speed (V++).

DOWN: The wheelchair moves backward.  & Decrease in linear speed (V−).

RIGHT: The wheelchair moves to the right. & Increase in angular speed (W++).

LEFT: The wheelchair moves to the left. & Decrease in angular speed (W−).

                         

 

 

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.We aim to improve the existing eye-tracking system and will attempt to resolve the current faults and weaknesses, and implement the eye-  tracking device in the most user friendly and efficient interface we can devise. We can also design many user friendly devices such as wheelchair  

Bibliography:

              Young and Sheena, "Survey of eye movements  recording methods"

              Behavior Research Methods and Instrumentation, Vol. 7 (5), 1975   Hutchinson

             "Human-Computer Interaction Using Eye-Gaze Input", IEEE

             Transactions on Systems, Man, and Cybernetics, Vol. 19, No. 6, 1989

             Bahill, A. T., Bioengineering: Biomedical, Medical and Clinical Engineering, Prentice-

            Hall, Inc., Englewood Cliffs, NJ, 1981.


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