Text Box: Assistive Environment Control Device for Quadriplegics Text Box: VI. Tongue Drive Assistive Technology In the Tongue Drive system, the motion of the tongue is traced by an array of magnetic sensors, which measure the magnetic field generated by a small permanent magnet that is contained within a biocompatible fixture similar to a tongue stud and pierced on the tongue. The magnetic sensors can be mounted on a dental retainer and attached on the outside of the teeth to measure the magnetic field from different angles and provide continuous real-time analog outputs. Sensor outputs are multiplexed, digitized, and transmitted wirelessly to an external controller unit. The signals received by an external controller unit in the form of a portable computer or personal digital assistant (PDA) are processed to indicate the motion of the permanent magnet and consequently the tongue position within the oral cavity. We can assign certain control functions to each particular tongue movement in software and customized the system for each individual user. These customized control functions may then be used to operate a variety of devices and equipments including computers, phones, and powered wheelchairs. The signals from the magnetic sensors are linear functions the magnetic field, which is a continuous position-dependent property. Thus a few sensors are able to capture a wide variety of tongue movements. This would provide a tremendous advantage over switch based devices in that the user has the options of proportional, fuzzy, or adaptive control over the environment. These would offer smoother, faster, and more natural controls as the user is saved the trouble of multiple on/off switch operations.

© 2006 Maysam Ghovanloo

Tongue Drive Assistive Technology consists of a permanent magnet pierced on the tongue and an array of magnetic sensors. 

Text Box: Related Publications: X. Huo, J. Wang, and M. Ghovanloo, “Using magneto-inductive sensors to detect tongue position in a wireless assistive technology for people with severe disabilities,” Proc. IEEE Sensors Conference, pp. 732-735, Oct. 2007 (First Place Poster Award). M. Ghovanloo, “Tongue operated assistive technologies,” Proc. IEEE 29th Eng. in Med. and Biol. Conf., pp. 4376-4379, Aug. 2007. X. Huo, J. Wang, and M. Ghovanloo, “A wireless tongue-computer interface using stereo differential magnetic field measurement,” Proc. IEEE 29th Eng. in Med. and Biol. Conf., pp. 5723-5726, Aug. 2007. X. Huo, J. Wang, and M. Ghovanloo, “Using magneto-inductive sensors to detect tongue position in a wireless assistive technology for people with severe disabilities,” To be presented at the IEEE Sensors Conference, Atlanta, GA, Oct. 2007. X. Huo, J. Wang, and M. Ghovanloo, “Use of tongue movements as a substitute for arm and hand functions in people with severe disabilities,” Proc. RESNA Conference, Phoenix, AZ, June 2007. X. Huo, J. Wang, and M. Ghovanloo, “A magnetic wireless tongue-computer interface,” Proc. 3rd Intl. IEEE/EMBS Conf. on Neural Engineering, pp. 322-326, May 2007. G. Krishnamurthy and M. Ghovanloo, “Tongue Drive: A tongue operated magnetic sensor based wireless assistive technology for people with severe disabilities,” IEEE Intl. Symp. on Circuits and Systems, pp. 5551-5554, May 2006. Text Box: I. Introduction Assistive technologies are critical for people with severe disabilities to lead a self-supportive life. Persons severely disabled as a result of causes ranging from traumatic brain and spinal cord injuries to stroke generally find it extremely difficult to carry out everyday tasks without continuous help. Assistive technologies that would help them communicate their intentions and effectively control their environment, especially to operate a computer, would greatly improve the quality of life for this group of people and may even help them to be employed.

© 2007 Maysam Ghovanloo
Text Box: II. Other Assistive Technologies A large group of assistive devices are available that are controlled by switches. The switch integrated hand splint, blow-n-suck (sip-n-puff) device, chin control system, and electromyography (EMG) switch are all switch based systems and provide the user with limited degrees of freedom. A group of head-mounted assistive devices has been developed that emulate a computer mouse with head movements. Cursor movements in these devices are controlled by tracking an infrared beam emitted or reflected from a transmitter or reflector attached to the user’s glasses, cap, or headband. Tilt sensors and video-based computer interfaces that can track a facial feature have also been implemented. One limitation of these devices is that only those people whose head movement is not inhibited may avail of the technology. Another limitation is that the user’s head should always be in positions within the range of the device sensors. For example the controller may not be accessible when the user is lying in bed or not sitting in front of a computer. Another category of computer access systems operate by tracking eye movements from corneal reflections and pupil position. Electro-oculographic (EOG) potential measurements have also been used for detecting the eye movements. A major limitation of these devices is that they affect the users’ eyesight by requiring extra eye movements that can interfere with users’ normal visual activities such as reading, writing, and watching. The needs of persons with severe motor disabilities who cannot benefit from mechanical movements of any body organs are addressed by utilizing electric signals originated from brain waves or muscle twitches. Such brain computer interfaces (BCI), either invasive or noninvasive, have been the subject of major research activities. Most BCI technologies are highly invasive (require a brain surgery) or heavily rely on signal processing and complex computational algorithms, which can results in delays and bulky system. That may also cost tens of thousands of dollars. Text Box: III. Why Tongue? Since the tongue and the mouth occupy an amount of sensory and motor cortex that rivals that of the fingers and the hand, they are inherently capable of sophisticated motor control and manipulation tasks. This is evident in vocalization and ingestion. The tongue is connected to the brain by the hypoglossal nerve, which generally escapes severe damage in spinal cord injuries. It is also the last to be affected in most neuromuscular degenerative disorders. The tongue can move very fast and accurately within the mouth cavity. It is thus a suitable organ for manipulating assistive devices. The tongue muscle is similar to the heart muscle in that it does not fatigue easily. Therefore, a tongue operated device has a very low rate of perceived exertion. Text Box: V. Prototype Tongue Drive System We have developed a prototype Tongue Drive system using off-the-shelf commercially available components to evaluate the feasibility and performance of this approach in developing assistive devices. The main purpose of the prototype device was to move a cursor on computer screen based on the location of a permanent magnet relative to four magnetic sensors. Four ratiometric linear sensors with 5 mV/G sensitivity were installed in cavities created in a mouth guard. The sensors readily provide temperature compensated linear voltage output proportional to the vertical magnetic field. The front two sensor outputs were used to control the cursor movements along the X direction and the rear two, movement along the Y direction. Text Box: III. Graphical User Interface A LabVIEW GUI has been developed for the prototype Tongue Drive system. It displays a large rectangular pink marker as a target in a random position for tracking by a smaller circular yellow cursor. Proportional control is incorporated in the system by accelerating the cursor (moving by a larger step-size) the closer the magnet is held to a sensor. The marker disappears and reappears at a different location when the user reaches it with the cursor and executes a “tongue click”. Left and right mouse-clicks are available in this system using the tongue movement. If the user quickly flicks the magnet towards one of the front sensors starting from a deadzone, it is considered a tongue click. These special tongue movements allow the user to “select” and “drag” an icon on screen represented by a target marker.

Tongue Drive GUI