A year ago we wrote about a new tongue controller designed to give quadriplegics the ability to operate external devices like wheelchairs and computers. Now results from a clinical trial testing the capabilities of the interface for the severely handicapped have been presented at the annual meeting of the Rehabilitation Engineering and Assistive Technology Society of North America (RESNA), and they show that the technology is intuitive and precise enough for patients to quickly become acquainted with it in a short period of time.
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 subject. 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.
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 personal 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 the subject 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 subject completed 40 trials for each time period.
After the computer sessions, the subjects were ready for the wheelchair driving exercise. Using forward, backward, right, left and stop/neutral tongue commands, the subjects maneuvered a powered wheelchair through an obstacle course.
The obstacle course contained 10 turns and was longer than a professional basketball court. Throughout the course, 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.
Each subject operated the powered wheelchair using two different control strategies: discrete mode, which was designed for novice users, and continuous mode for more experienced users. 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.
“Discrete mode is a safety feature particularly for novice users, but it reduces the agility of the wheelchair movement,” explained Ghovanloo. “In continuous mode, however, the user is allowed to steer the powered wheelchair to the left or right as it is moving forward and backward, thus making it possible to follow a curve.”
Each subject completed the course at least twice using each strategy while the researchers recorded the navigation time and number of collisions. 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.
Press release: Tongue Power: Clinical Trial Shows Quadriplegic Individuals Can Operate Powered Wheelchairs and Computers with Tongue Drive System…
Flashback: Tongue Controller Promises Better Device Interaction for Severely Disabled…