Abstract
Blind people need to become as independent as
possible in their daily life in order to guarantee a fully social
inclusion. Mobility means the possibility of freely moving,
without support of any accompanying person, at home, in public
and private buildings, and in open spaces, as the streets of the
town. Mobile and wireless technologies, and in particular the
ones used to locate persons or objects, can be used to realize
navigation systems in an intelligent environment. Such systems
open new opportunities to improve the speed, easiness, and safety
of the visually impaired persons mobility. Using these
technologies together with Text To Speech systems and a mobilebased
database the authors developed a cost effective, easy-to-use
orientation and navigation system: RadioVirgilio/SesamoNet1.
The cost effectiveness is due to the recovery of RFID identity tags
from cattle slaughtering: these tags are then borrowed to create a
grid used for navigation. In this paper the results of an usability
analysis of this guide system are presented. A preliminary
experiment involving a small group of experts and a blind person
is described. In order to evaluate the usability, three cognitive
walkthrough sessions have been done to discuss the system’s
basic functionality and to highlight the most critical aspects to be
modified.
Keywords- Blind mobility; Mobile communication and devices;
RFID; Usability test;
I. INTRODUCTION
A. Perceiving spaces by blind people
Blind people compensate the lack of sight augmenting the
capabilities of the other senses. In this way they are able to
create mental maps from sensory images [5]. In fact all the
remaining senses, mainly tact and hearing, but also in some
cases the olfaction, are used to replace, even if an incomplete
way, the ability to perceive the spaces. In order to know an
environment a visually impaired tries to build mentally the
spaces by identifying obstacles around him and progressively
searching environmental information.
B. Mobility and orientation by blind people
Orientation is the subjective ability to know the own
positioning in a space both in absolute sense and respect to the
point of departure and the one of arrival; this is possible
through a complex cognitive and perceptive process and by the
acquisition of the sensory information coming from the
environment and the body. A blind person can orient himself
in already known places by recognising known features
(absolute orientation) or by perceiving unknown but regular
objects, like buildings’ walls in outdoor situations or the angles
of a room walls in indoor spaces (relative orientation). This
first kind of orientation is, for a blind person, the most difficult
one due to the complexity of collecting information from the
surrounding environment only through tact and hearing. In
order to explore unknown places a blind person usually needs
to be guided by another person or a dog.
In order to move without a guide in an unknown space a
blind needs to identify some points of reference that allow him
to guess the optimal movements and the distance to cover to
move from one place to an other one. A visually impaired
decide her orientation from two types of information: the points
of reference and the lines of reference [12]. Points of reference
are every kind of environment information (tactile, acoustic or
olfactory) a blind person easily perceive and/or remember in
her memory: a visually impaired, has to knows his relative
position with respects to these points and their meaning.
Reference lines are based on a continuous environmental
knowledge that allows a blind to orient himself and to maintain
the right direction without the need of additional points of
reference, example are the sidewalks, the walls, the changes of
ground surface. RadioVirgilio/SesamoNet, through the voice
synthesized instructions, supplies to the most important points
of reference when the user cannot easily perceive these natural
marks and generates sounds to identify additional and useful
reference lines.

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