EagleEyes
EagleEyes:

An Eye Control System for Persons with Disabilities

by


James Gips and Peter Olivieri

Computer Science Department
Boston College
Chestnut Hill, Mass. 02167

Presented at

The Eleventh International Conference on

Technology and Persons with Disabilities

Los Angeles
March 1996



Introduction

EagleEyes [1] is a new technology that allows a person to control the computer simply by moving his or her eyes or head. The technology is based on the measurement of the EOG, or electro-oculographic potential, through electrodes placed on the head. For the past year we have been working with people with severe disabilities to try out the system and to teach them how to use the system to control the computer. The current system runs on a Macintosh and allows us to run both custom-developed software and most commercial software. Through EagleEyes, people can run educational and entertainment software, spell out messages, and navigate through the internet just by moving their eyes.


Table of Contents


Sensing Eye Movements

There are several approaches to sensing eye movements. [2]

Most approaches involve the use of a camera or imaging system to visually track some feature of the eye and then a computer or some electronics to do the reverse geometry to determine where the user is looking. Several systems use of infrared illumination and an infrared-sensitive video camera. The ISCAN system [3] uses a lightweight head-mounted infrared-sensitive camera to track eye movements. The Erica system [4, 5] uses an infrared-sensitive camera mounted below the computer monitor. Canon has developed a miniaturized system that allows some of its cameras (for example, the EOS A2E and the newer EOS ELAN IIE) to sense where the user is looking so the camera can autofocus along that sight line [6]. There also is work on systems that use visual light, rather than infrared. Pomerleau and Baluja [7] reported using a neural network to process ambient light video camera images of the eye to determine where the user is looking.

The approach we are taking is to attach electrodes next to the eyes and use them to sense the EOG or electro-oculographic potential. The EOG is also known as the ENG or electronystagmographic potential. The EOG / ENG has been investigated for over 70 years [8,9]. Currently the major use of the EOG / ENG is in diagnosing vestibular and balance problems [10]. A similar approach to ours is taken in the EyeCon / Biomuse system [11].

The EagleEyes System

With the EagleEyes system, five electrodes are placed on the head of the user. An electrode is placed 1 cm. above the right eyebrow and another 2 cm. below the right eye. Electrodes are placed 2 cm. to the right and left of the outer canthi. A fifth electrode is placed on the user's forehead or ear to serve as a ground. (See Figure 1) The leads from these electrodes are connected to two Grass Instruments 7P122 differential amplifiers, which amplify the signals by a factor of 5,000. The amplifier outputs are connected to an analog-to-digital converter on a National Instruments signal acquisition board in a Macintosh computer. A system diagram is given in Figure 2.

Figure 1. Alexa with electrodes, ready to use EagleEyes.


Figure 2. EagleEyes system diagram
Custom software interprets the two signals and translates them into cursor coordinates on the computer screen. The electrodes placed around the eyes measure the electro-oculographic potential, the variation in the standing potential between the retina and the cornea. The EOG is a function of the position of the eye relative to the head. Basically, the difference between the voltages of the electrodes above and below the eye indicates the vertical position of the eye relative to the head. The difference between the voltages of the electrodes to the left and right of the eyes indicates the horizontal position of the eye relative to the head. Move your eyes up and the vertical signal increases. Move your eyes to the left and the horizontal signal increases. The EOG signal changes approximately 20 microvolts for each degree of eye movement. In our system the signals are sampled 60 times per second.

The EagleEyes system software allows us to run EagleEyes with most existing commercial software. Our system software runs in the background. Every 1/60th of a second it springs to life, senses the two values on the A/D converter, translates the values into screen coordinates, and saves them as the official mouse coordinates in the system. An option in the software allows a mouse click to be generated whenever the cursor remains within a settable small radius on the screen for a certain period of time. That is, the user can generate a click by staring at a spot on the screen for a certain fraction of a second. The software can run in the background with any well-behaved application. Thus, Macintosh software, whether commercial or custom-developed, can be run by eye control instead of mouse control.

We currently have three EagleEyes systems, two in our laboratories and one in the Campus School. The Campus School is a day-time educational facility for students, aged three to twenty-two, who have multiple impairments. It is part of the School of Education at Boston College and is located on the main campus. The EagleEyes facility at the Campus School is reserved for the Campus School students in the morning and for visitors and mainstreamed students from the greater Boston area in the afternoon.

Using EagleEyes

The EagleEyes system tracks the EOG, which is proportional to the angle of the eye in the head. Learning to use the EagleEyes system is an acquired skill.

A person without disabilities usually requires about 15 minutes to learn to use the system and to become proficient enough to spell out her name using a board like the one in Figure 3.

Figure 3. Spelling out a message.

For a new user we usually explain that the system is measuring the angle of the eye in the head and that the cursor can be moved either by holding the head constant and moving her eyes or by fixing her eyes on a spot in the screen and by moving her head or by some combination of the two. New users practice moving a cursor on a blank screen and then play a simple video game we have developed for training. When a user is proficient enough to shoot down 9 out of 10 aliens in the video game, then the user is proficient enough to be able to spell and use the other software.

Dozens of people with disabilities, mostly quite severe, have tried the system. They can require anywhere from 15 minutes to months to gain proficiency with the system. We currently have about a dozen profoundly disabled youngsters using the EagleEyes system on a regular basis. [12, 13].

The Human Computer Interface

A major challenge has been the design of the human-computer interface. That is, given the capabilities of people to control their eyes and head and given the physical characteristics of the EagleEyes system, the amplifiers and so forth, how should the software be designed so that it is easy for people to use ? Jacob [14, 15] points out important potential benefits and problems of using eye movements to control computers. For example, he discusses the "Midas Touch problem":

"At first, it is empowering to be able simply to look at what you want and have it happen, rather than having to look at it (as you would anyway) and then point and click it with the mouse or otherwise issue a command. Before long, though, it becomes like the Midas Touch. Everywhere you look, another command is activated; you cannot look anywhere without issuing a command. The challenge in building a useful eye tracker interface is to avoid the Midas Touch problem. [14, p. 156]

Starker and Bolt [16] describe an information display system that makes real-time inferences, using an eye-tracking system, about a user's interests and modifies the display, for example by zooming in on an item inferred to be of interest. Nielsen [17] discusses the trend towards "noncommand user interfaces" and the place of eye-tracking in these systems.

Generally the software used with EagleEyes must be controllable by large buttons or clickable areas. The basic issue is accuracy and control. With EagleEyes, the user can move the cursor with fair accuracy and can issue a single mouse click. We have not devised an effective way for the user to simulate holding down the mouse button or issuing a double click. So, for example, the EagleEyes user cannot yet control pull-down menus.

We have developed and used several types of software with the system.

Future Developments

We are in the process of developing a miniaturized version of EagleEyes. We expect this version will work with notebook computers and be a totally portable system. We hope to be able to provide our students with their own EagleEyes system to use at home, in school and wherever else they travel.

[References]


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