04-05-2011, 04:10 PM
Introduction and preliminary evaluation of the Tongue Drive System:
Wireless tongue-operated assistive technology for people with little or
no upper-limb function
Abstract—
We have developed a wireless, noncontact, unobtrusive,
tongue-operated assistive technology called the
Tongue Drive System (TDS). The TDS provides people with
minimal or no movement ability in their upper limbs with an
efficacious tool for computer access and environmental control.
A small permanent magnet secured on the tongue by implantation,
piercing, or tissue adhesives is used as a tracer, the movement
of which is detected by an array of magnetic field sensors
mounted on a headset outside the mouth or on an orthodontic
brace inside. The sensor output signals are wirelessly transmitted
to an ultraportable computer carried on the user’s clothing
or wheelchair and are processed to extract the user’s commands.
The user can then use these commands to access a
desktop computer, control a power wheelchair, or interact with
his or her environment. To conduct human experiments, we
developed on a face shield a prototype TDS with six direct
commands and tested it on six nondisabled male subjects. Laboratory-
based experimental results show that the TDS response
time for >90% correctly completed commands is about 1 s,
yielding an information transfer rate of ~120 bits/min.
Key words: assistive technologies, computer access, environment
control, information transfer rate, magnetic field sensors,
permanent magnets, rehabilitation, telemetry, tongue control,
wireless.
INTRODUCTION
Persons with disabilities as a result of various causes,
from traumatic brain injury and spinal cord injury (SCI)
to amyotrophic lateral sclerosis and stroke, generally find
performing everyday tasks extremely difficult without
continuous help [1–3]. In the United States alone, an estimated
11,000 new cases of SCI are added every year to a
population of a quarter of a million as a result of acts of
violence, falls, and accidents [2]. Fifty-five percent of
SCI patients are between 16 and 30 years old and will need
lifelong special care that currently costs about $4 billion
each year [3]. With the help of assistive technologies (ATs),
people with severe disabilities can lead self-supportive,
independent, and high-quality lives. ATs can not only ease
these individuals’ need to receive continuous help, thus releasing a family member or dedicated caregiver and
reducing their healthcare costs, but may also provide
them with opportunities to return to full, active, and productive
lives within society by helping them to be
employed.
Although many devices are available to assist people
with lower levels of disabilities, people who have minimal
or no movement ability (e.g., individuals with tetraplegia)
and who probably need assistance the most have
very limited options. Even the existing ATs for this group
of people have limitations such that only a small number
have become popular among their intended users. The
sip-n-puff switch, for example, is a simple, easy-to-learn,
and relatively low-cost AT. However, it is slow, cumbersome,
and inflexible, with only 2 to ~4 direct commands
[4].* It also requires its users to have airflow and diaphragm
control, which patients who use ventilators do
not have.
Another group of ATs tracks eye movements from
corneal reflection and pupil position [5–6]. Electrooculographic
potentials have also been used to detect eye
movements [7–8]. An inherent drawback of these methods
is that they interfere with the users’ vision by requiring
extra eye movements for eye control. In many cases,
whether the user is issuing a command or simply gazing
at an object is not clear; this is also known as the “Midas
touch” problem [9]. Head pointers, another group of ATs,
require a certain level of head movement ability that may
not exist in many patients with high-level SCI [10].
These devices also require the user to always be in a sitting
position while using them.
Some ATs, such as electroencephalogram (EEG) systems,
directly use brain waves [11]. These devices
require user concentration, a long procedure for electrode
attachment, and daily removal. EEG systems are also
prone to external interference and motion artifacts due to
the small magnitude of the EEG signals. More recently,
invasive brain-computer interfaces (BCIs) have emerged
based on subdural electrocorticograms or intracortical
neural recording [12–15]. These procedures are highly
invasive, costly, and involve risks associated with brain
surgeries. Finally, voice-activated ATs are quite popular
for computer access and operate well in quiet settings.
However, they are unreliable in noisy and outdoor environments.
They also require diaphragm control, similar
to the sip-n-puff, and functional vocal cords [10].
The tongue and mouth occupy an amount of sensory
and motor cortex in the human brain that rivals that of the
fingers and the hand. Hence, they are inherently capable
of sophisticated motor control and manipulation tasks
with many degrees of freedom [16]. The tongue is connected
to the brain by the hypoglossal nerve, which generally
escapes severe damage in SCI. The tongue muscle
is similar to the heart muscle in that it does not fatigue
easily [17]. Further, the tongue is noninvasively accessible
and not influenced by the position of the rest of the
body, which can be adjusted for maximum comfort.
The just-named reasons have resulted in the development
of a few tongue-operated ATs, such as the Tongue
Touch Keypad (TTK).† Despite being innovative for the
time in which it was introduced (early 1990s), the TTK
has not been widely adopted because it is bulky and
obtrusive [17]. TonguePoint is another AT, based on the
IBM TrackPoint device used in laptops, and takes the
form of a small pressure-sensitive joystick placed inside
the mouth [18]. Even though this device provides proportional
control, it is always restricted to a joystick operation
and any selection or clicking must be performed
through additional switches. The tip of the joystick also
protrudes about 1 cm into the mouth, which could interfere
with speech and ingestion. A few other tongue- or
mouth-operated joysticks have been developed, such as
Jouse2 and IntegraMouse.‡ These devices can only be
used when the user is sitting and require a certain level of
head movement to grab the mouth joystick if the stick is
not to be held inside the mouth at all times
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