Download full issue (PDF 2.1MB) - Council of European ...

Information Technologies for Visually Impaired People
form users about how far away the obstacle is. One of the
difficulties preventing these devices from being more widely
adopted is the need for specialized training in their use.
The use of satellite positioning (GPS) and orientation
devices open up further perspectives, although there are still
some unresolved problems since in built-up areas the presence
of buildings can interfere with satellite signals, especially
on pavements. These devices can also be linked to
mobile telephones capable of transmitting images, which
enables users to summon remote human aid.
2 Information Access Systems
Direct Transduction
Direct transduction devices convert visual information
into information that is accessible to the blind. They do not
use intelligent processing systems, but depend simply on
energy transformation. This technology is often referred to
as sensory substitution.
Tactile Stimulation
The first intuitive was in this sense to convert visual
information directly into tactile stimulation, thereby respecting
the two dimensions of shapes. The sense of touch is
made up of nerve endings that can detect various sensations
(cold, heat, pressure, etc.). It is important to know the
exact nature of these nerve endings so as to be able to
optimize their stimulation. One important feature is their
spatial distribution frequency, especially of pressure sensitive
receptors. In 1 cm 2 the fingertip there may as many
pressure receptors as in 200 cm 2 of any other part of the
body. Another important feature is that tactile sensory cells
act on an On/Off basis, emitting an action potential when
they are stimulated and also when they cease to be stimulated
(for example, they "notice" when you put on a pair of
glasses or a hat, and when you take them off, but not while
Figure 2: Blind Man Led by two Hens.
Figure 3: Teletact.
you are wearing them). For this reason stimulation must be
effected by prompting an exploration with movements or
by making the stimulators vibrate.
Around 1880 Camile Grim presented his "Anoculoscope",
a prototype of 64 (8x8) light sensitive selenium cells which
used electromagnets to activate an identical number of stimulating
tactile pins according to the light that fell on matrix of
cells[3].
Later other experiments focused on stimulation of the
user’s back or tummy as can be seen in Figure 4 [4].
In the seventies another device appeared; the Optacon (see
Figure 5), developed by Telesensory Corp. This was a device
comprising a camera with 6x24 receptors connected to a screen
with an identical number of vibrating pins that allowed the
user to feel the shape by stimulating a finger. It was successfully
marketed until the turn of the century. It enabled users to
access documents, for example, after a basic training course,
although reading speed remained slow and the process was
tiring. A miniaturized camera was located on two rollers to
make it easy to move along the line and it was equipped with a
zoom and an adjustable tactile screen (frequency and intensity
of vibration, inverse stimulation, etc.).
Some research going on today in the field of visio-tactile
sensory substitution is focusing on stimulating the underside
of the tongue[5].
Acoustic Stimulation
Another possibility of stimulation, although of a more
abstract nature, is acoustic stimulation . In this case the idea
is to transmit bi-dimensional information via a one dimensional
channel such as hearing. However, by analyzing the
frequency of such signals we can achieve a pseudo two dimensional
encoding. The first research into this type of sensory
substitution is attributed to Fournier d’Albe [6], who
invented and perfected [7] the "Optophone" for which reading
speeds of up to 60 words a minute were claimed [8]
6 UPGRADE Vol. VIII, No. 2, April 2007 © Novática