A CURRENT PROJECT BEING DONE UNDER
INDIAN INSTITUTE OF TECHNOLOGY, MADRAS
(IITM)
TITLE:
EYE INTERFACE TECHNOLOGY
ELECTRO OCULOGRAPHY
---------control of computer with eyes
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. In this paper I come before with a new
model of based on Electro-Oculography which uses Electro-oculogram Bio
potential amplified signal to control computer .I also discuss its
implementation details, including software and hardware design. As my
contribution to this paper I introduce a new keyboard design, some
modifications in design to overcome the drawbacks in existing model
In single statement our paper
deals with controlling, operating computer with the aid of eyes and this was
the project which was done under the precise guidance of Indian institute of
technology madras (IITM) in which a live working model costs around 10 lakhs is
being built. All the rights of this project strictly belong to IIT, Madras.
In this paper I provide the following
details:
1.
Introduction
2.
Electro Oculography: Principle
3.
Design concepts
4. Interaction of user with
system
5. Word
processor
6.
De-merits
7.
Possible near future improvement
8.
Performance issues
9.
Conclusion
10. Bibliography
Introduction
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. 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.
II. 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.
III. 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
figure : Block Diagram of the Design
considerations
The Erica workstation, or eye-gaze
response interface computer aid, is an example worthy of study. Erica is based
on a standard personal computer specially adapted with imaging hardware and
software through near-infrared reflectometry.
Monitor Geometry:
Take a 19 inch monochrome display with typical pixel configuration of
1024x768 at 72 dpi, for an active display area of 14.22x10.67 inches. When
centrally viewed from a distance of 2 feet, this region subtends an angle of 25
degrees vertically, and 33 degrees horizontally. Maximum EOG or reflect metric resolution is
about 1-2 degrees; with menu boxes generously separated by 3 degrees, the 19
inch display still has sufficient room for a 10x4 matrix of directly selectable
keys - leaving the entire bottom half of the screen available for a text
display area and other controls better. Keyboard implementations should
definitely be possible. Fukuda and Yamada is the other selection method.
Distinguish between routine eye function and an intentional selection action is
necessary. Perhaps the most significant item in this entire project,
inexplicably absent from any other eye-controlled system, is the proposed use
of a unilateral blink as that selection action. Blinking normally occurs every
few seconds, either consciously or unconsciously - but always bilaterally.
Blinks are easily detected by EOG as sharp, strong pulses in the vertical
channel; since vertical eye movement is always conjugate, a pulse in only one
vertical channel is unequivocally a unilateral wink Actual Method: With a 19
inch monitor as described above, a two level keyboard could be laid out in a
10x4 menu box matrix; the bottom half of the screen could display about 25
complete lines of text, and still have additional file, paging, or main menu
controls off to the side. The first level of the keyboard would contain all the
alphabetic characters, common punctuation, and cursor keys; selecting a special
"shift" key would display the second level of the keyboard, with the
numbers and less commonly used symbols or editing functions.
IV. 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.
Figure: Placement of Transducer Pickups to
Measure Eye Movements
Figure: 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 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.
V. System Design for Location
Specification using EOG
The work related to the proposed system
involves both hardware and software design and development.
The system
architecture is shown in Figure
.
The hardware part of the
system is fairly straightforward. We have completed the design of the amplifier
and filter sections and assembled a crude circuit for testing and data
collection. 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. Thus we have chosen to do most
of the filtering and noise removal in software. The actual hardware fabricated amplifies the
voltage picked up by the transducer, removes the electrical line frequency (60
Hz notch filter), 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
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.
The second interaction mode is the
command mode, where the cursor is moved by the system to track the user's gaze.
In our example interface, shown in Figure 3, we show four command "buttons."
The cursor is at the center of display (the cross). Imagine that this command
system controls a machine, whose speed can be changed. So 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. Another technique is for
transmitting commands. This too should be fairly easy to distinguish from
natural eye blinks. When the head is turned away from the screen, the system
will be able to detect this because the fixated distance changes from the
"norm" recorded during calibration. This will cause the system to
disengage and freeze the cursor on the screen. To re-engage the user should perform
a gesture such as fixating on the cursor and winking twice
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).
VI. 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. The system block diagram is
shown in Figure 2 and discussed in Section 5.
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 equipment setup so that real time
signal acquisition could take place. This involved assembling the electrodes,
constructing the analog and A/D circuits on a PC form factor board, and
interfacing and installing it on the PC bus. The PC was then linked to the SUN
via a serial (19.2 Kb) line. Routine software has been developed to enable a program
running on the SUN to access the eye movement data captured on the PC and
transmitted on the serial line.
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.
VII. Possible Near Future
Improvements
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). This
improved board will eventually drive to finer resolution on the screen. The
software is being revised to enable better results as well. This will take form
in the way of defining optimal parameter choices for the various thresholds and
sampling rates, as well as some other minor software improvements. 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.
VIII. 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.
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.
