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Definitions
and Distinctions
 One source
of never-ending confusion and unnecessary complexity in the world
of AT interfaces is the absence or misuse
of standard terminology.
Clear nomenclature, used consistently, could simplify the task
of the service provider engaged in AT selection, modification
and delivery.
Not only does it make communication with other professionals,
sales people, rehab engineers and manufacturers less ambiguous,
it also
makes it clearer that despite the numerous differences of detail
that are readily apparent among user interfaces, there are relatively
few generalizable categories under which all products can be
grouped. Some of the most important of these definitions and
distinctions
are listed and explained below.
This terminology
is not the invention of this writer. The reader may find, however,
that not all of
this conceptual language is
used consistently in the world of AT. It is used by rehab engineers,
interface
designers, many Occupational Therapists, some vendors and others.
Our purpose here is to provide the reader with an exact and
internally consistent nomenclature that will serve well in her/his
analysis
and categorizing of AT interfaces.
Sensor: Sensors
are the actual bits of technology that are designed and placed
to be sensitive
to user actions and convert
those
actions to electrical signals as input to the AT. So, for
example, in a
puff-sip control interface for a power wheelchair, the component
at the end
of the tube that reacts to changes in pressure is the “pressure
sensor”. The lapel microphone in a voice-activated
system is the sensor. So is the little finger-tip joystick
that senses
cursor-control
forces on a laptop computer keyboard, and the image detector
that senses that the user’s gaze has shifted in an
eye-movement-based AAC system. “Transducer” is
another word for sensor.
Control
Site and Sensed Variable: This is definitely not standard terminology;
but we need
some wording to use consistently
below.
By “control site”, we will mean a part of the
AT user’s
body or measurable motor function used to operate an input
interface. So, for example: thumb and forefinger for a small
joystick; jaws
and head for a mouth stick; vocal apparatus for a voice-input
system; lips for a puff-sip interface; etc. Often it will
be relevant to
discuss the actual quantity that is measured or detected
by the sensor. This “sensed variable” might be
grip force for a squeeze bulb placed in the palm of the hand
(the control site); myoelectric
activity (actually the voltage thereof) in the biceps for
a powered elbow prosthesis; or the angle of gaze relative
to the head for
an eye-movement based system in which the sensor is mounted
on an eyeglass
frame.
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