Georgia Tech assistant professor
Maysam Ghovanloo points to a
magnet on graduate student
Xueliang Huo's tongue
that helps direct the chair
(GA Tech Photo: Gary Meek)
Tongue Drive System: New Mobility for People With Spinal Cord Injuries
July 08, 2009
People with spinal cord injuries can successfully drive a powered wheelchair and even maneuver curves, using tongue movements, according to the results of a recently completed clinical trial.
"This clinical trial has validated that the Tongue Drive system is intuitive and quite simple for individuals with high-level spinal cord injuries to use," said Maysam Ghovanloo, lead author of the study and assistant professor in the School of Electrical and Computer Engineering at the Georgia Institute of Technology.
He says that participants in his study were able to easily remember and correctly issue tongue commands to play computer games and drive a powered wheelchair around an obstacle course with very little prior training.
At the annual conference of the Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) on June 26, the researchers reported the results of the first five clinical trial participants to use the Tongue Drive system.
The trial was conducted at the Shepherd Center, an Atlanta-based catastrophic care hospital, and funded by the National Science Foundation and the Christopher and Dana Reeve Foundation.
The study tested the ability of these individuals with tetraplegia, as a result of high-level spinal cord injuries (cervical vertebrae C3-C5), to perform tasks related to computer access and wheelchair navigation using only their tongue movements.
At the beginning of each trial, Ghovanloo and graduate students Xueliang Huo and Chih-wen Cheng attached a small magnet the size of a grain of rice to the participant's tongue with tissue adhesive. Movement of this magnetic tracer was detected by an array of magnetic field sensors mounted on wireless headphones worn by the study participants. The sensor output signals were wirelessly transmitted to a portable computer, which was carried on the wheelchair.
The signals were processed to determine the relative motion of the magnet with respect to the array of sensors in real-time. This information was then used to control the movements of the cursor on a computer screen or to substitute for the joystick function in a powered wheelchair.
Details on use of the Tongue Drive for wheeled mobility were published in the June 2009 issue of the journal IEEE Transactions on Biomedical Engineering.
Why Choose the Tongue?
Ghovanloo chose the tongue to operate the system because unlike hands and feet, which are controlled by the brain through the spinal cord, the tongue is directly connected to the brain by a cranial nerve that generally escapes damage in severe spinal cord injuries or neuromuscular diseases.
Before using the Tongue Drive system, the subjects trained the computer to understand how they would like to move their tongues to indicate different commands. A unique set of specific tongue movements was tailored for each individual based on the user's abilities, oral anatomy and preferences.
For the first computer test, the user issued commands to move the computer mouse left and right. Using these commands, each subject played a computer game that required moving a paddle horizontally to prevent a ball from hitting the bottom of the screen.
After adding two more commands to their repertoire--up and down--the subjects were asked to move the mouse cursor through an on-screen maze as quickly and accurately as possible.
Then the researchers added two more commands--single and double mouse clicks--to provide study participants with complete mouse functionality. When a randomly selected symbol representing one of the six commands appeared on the computer screen, the subject was instructed to issue that command within a specified time period. Each participant completed 40 trials for each time period.
An Obstacle Course
After the computer sessions, patients were ready for the wheelchair driving exercise. Using forward, backward, right, left and stop/neutral tongue commands, they maneuvered a powered wheelchair through an obstacle course.
The collision course contained 10 turns and was longer than a professional basketball court. Throughout the exercise, the users had to perform navigation tasks such as making a U-turn, backing up and fine-tuning the direction of the wheelchair in a limited space. Subjects were asked to navigate through the course as fast as they could, while avoiding collisions.
Continuous Mode for Curves
Each patient operated the powered wheelchair using two different control strategies: discrete mode, which was designed for novice users, and continuous mode for the more agile crowd.
In discrete mode, if the user issued the command to move forward and then wanted to turn right, the user would have to stop the wheelchair before issuing the command to turn right. The stop command was selected automatically when the tongue returned to its resting position, bringing the wheelchair to a standstill.
In continuous mode, the user is allowed to steer the powered wheelchair to the left or right as it is moving forward and backward, making it possible to navigate a curve.
Each patient completed the course at least twice using each strategy while the researchers recorded the navigation time and number of collisions incurred. Using discrete control, the average speed for the five subjects was 5.2 meters per minute and the average number of collisions was 1.8. Using continuous control, the average speed was 7.7 meters per minute and the average number of collisions was 2.5.
While this initial performance trial only required six tongue commands, the Tongue Drive system can potentially capture a large number of tongue movements, each of which can represent a different user command.
Better Than a Straw
The ability to train the system with as many commands as an individual can comfortably remember and having all of the commands available to the user at the same time are significant advantages over the common sip-n-puff device that acts as a simple switch controlled by sucking or blowing through a straw, Ghovanloo says.
Some sip-n-puff users also consider the straw to be a symbol of their disability. Since Tongue Drive users wear headphones, commonly worn by music listeners, or mobile phone users, this system makes patients feel more like everyone else, researchers say.
A future system upgrade will be to move the sensors inside the user's mouth, according to Ghovanloo. This will be an important step for users who are very impaired and cannot reposition the system for best results.
Source: Georgia Institute of Technology.