![Prototype of assisive device offering to the blind people the opportunity to develop in its surroundings through the recreation of the spaceby means of sound 3D [8].](https://www.researchgate.net/profile/Stanislav-Vitek/publication/252053649/figure/fig1/AS:450497661411329@1484418420351/Prototype-of-assisive-device-offering-to-the-blind-people-the-opportunity-to-develop-in_Q320.jpg)
Content uploaded by Stanislav Vitek
Author content
All content in this area was uploaded by Stanislav Vitek on Jan 14, 2017
Content may be subject to copyright.
New Possibilities for Blind People Navigation
Stanislav Vítek1, Miloš Klíma2, Libor Husník3, Daniel Špirk
1Czech Technical University in Prague, Technická 2, Prague
viteks@fel.cvut.cz
2Czech Technical University in Prague, Technická 2, Prague
klima@fel.cvut.cz
3Czech Technical University in Prague, Technická 2, Prague
husnik@fel.cvut.cz
Abstract – This paper deals with the design and
implementation of the device aimed to navigation
of visually impaired people. First part of the article
presents a review of existing assistance devices for
visually impaired, in the second part follows
description of the system using low-cost input and
output personal computer interfaces (joystick,
video grabbers, NVIDIA 3D Vision) and
description of design of novel acoustic transducers,
focused for use in aids for the blind.
I. INTRODUCTION
According to the World Health Organization [1],
there are about 314 million visually impaired people
in the world, 45 million of them are blind. About 87%
of visually impaired live in developing countries.
These people are faced with huge difficulties while
moving in cities on their own. Typically 75% of blind
people are declaring that they need assistance for their
daily life.
Blind people can generally remember their way to
limited number of know places, but the fear of
unknown often lead to reducing of their mobility.
Mobility can be improved using leader dogs, which
can help blind people avoid obstacles and find their
way in unknown environment. The bottleneck of this
solution is price of leader dog, for example in Czech
Republic it is around 7500 EUR. Although several
organizations are financially supporting blind people,
only few of them can actually have leader dog.
With the white cane, the most used aid instrument,
impaired can feel silent obstacles at the cane’s length
distance, so their anticipation capability is very poor.
It is important to notice that white cane is not only
useful obstacle detector, but also a means by which
blind people are recognized by sighted people.
From this reason a lot of assistive devices and
system aim to help blind people achieve mobility
(Electronic Travel Aids – ETA and Electronic
Orientation Aids – EOA) have been developed.
Different technologies including Location Based
Services (and similar technologies like GSM
localization, GPS or RFID), artificial vision and
obstacles detection sensors (laser, sonar). The state of
art shows that assistive devices do exist. However
none of them can solve problem of loosing orientation
in known environment, which is temporarily changed
(borrow pit, temporarily closed exit from public
building, palisade etc.). Last but not least psychical
support is necessary – blind user should have feel of
assistance.
II. STATE OF ART
Assistance devices designed to aid visually
impaired people need to deal with two different
issues: at first they need to capture contextual
information (distance of obstacle, position of user,
environment around user), at second they need to
present user with this information. Presentation
method must be adopted to blind users and must be
suitable for continuous use. It generally means that
system should be fast in order to cut user from
obstructions, information have not to be too much
detailed in order to keep user’s perception channels
free and finally passing of the information must be
well pronounced.
From the point of view of the contextual
information capturing, assistive system can be divided
into two main groups: independent autonomous
devices and devices with navigation centre, i.e. with
human interaction.
Into the first group belongs white cane with
several improvements like infrared or ultrasonic
sensors and newly canes with camera. Very
interesting is utilization of RFID tags: however RFID
is technology originally designed to tagging to
commodity stuff, can be usefully utilized to help
visually impaired people. As an example can be
mentioned Czech project RF guide [2] allows blind
users to have orientation in buildings (RFID tags are
glued on the floor and user equipped with special
electronic cane following them) of project
NAVIBELT [3] using PDA mapping GIS
(Geographic Information System) information into the
RFID information grid.
Unfortunately RFID chips still have extremely
poor radius – passive RFID have radius around 10cm,
active RFID with batteries have larger radius but
bigger price indeed. Interesting are projects working
on similar principle as RFID but with different
resources. French system RAMPE, intended to equip
bus and tramway stop with base stations, providing
information about transport trough local Wi-Fi
network into the user’s PDA device with Text To
Speech software [4].
Into the second group belongs for example GPS
based navigation in combination with GSM or GPRS
modem for transmission of telemetry data and voice
contact with blind user. The system allows estimate
position of the user with accuracy of tens of
centimeters. Operator in navigation centre can use this
information during voice contact after user’s
emergency call. The route scheduler is interesting
supplement of service (thanks to Text To Speech
technology device verbally navigate blind user).
There is Navigation centre SONS CR [5] in Czech
Republic, operated in cooperation with Research and
Development Center of CTU in Prague a and
Vodafone.
For the information presentation existing devices
use ether audio or tactile interfaces. Devices in first
case typically utilize strike note signalization with one
small speaker: for example Teletact 1 [6] uses 28
different musical notes (flute sounds over four octaves
ranging from 131 Hz to 2.1 kHz) which correspond to
28 intervals of distance. Devices using stereo
earphones are also know – here is navigation done by
spatial sound synthesis using Head Related Transfer
Function [7].
Fig. 1. Prototype of assisive device offering to the blind people the
opportunity to develop in its surroundings through the recreation of
the spaceby means of sound 3D [8].
The audio interfaces has various defects: user can
recognize difference between musical sounds and
street sounds, but when the ambient noise level often
fluctuates, it is very difficult to adjust proper audio
level of navigation sounds. To avoid the difficulties
inherent to audio interfaces a lot of devices propose
tactile interfaces, generally in addition to an audio
interface.
III. PERSONAL HELP FOR BLIND USERS
The main goal of here presented project (in
following text we will use acronym PERSEUS) is to
help blind people in serious troubles [9]. Our
approach is combination of several previously
mentioned principles. The main part of the user’s
device are acrylate protective glasses, used as a holder
for two cameras (see Fig. 3).
In the case of emergency user send signal to the
navigation centre, where operator can watch
stereoscopic video simulating vision of sighted
people. Stereoscopic video stream is transmitted to
the operator with public WiFi network. Operator see
context of environment in 3D (using NVIDIA 3D
vision system) so can estimate distance of obstacles.
For navigation of user acoustic beacon is used.
Fig. 2. Arrangement of whole proposed system
Operator has the joystick and through the use of
the simple protocol is handling choice of audio
sample in the memory of user wearable PC.
Artificially generated audio samples simulate virtual
source of audio signal, which navigate direction of
user’s walk. Angular resolution is about 5 degrees in
azimuthal plane with real audio source and it is
generally possible reach that resolution with artificial
source [10]. For the listening of virtual audio source is
user using novel acoustic transducers (read part 4 of
the article and see Fig. 4).
In the very first prototype are used miniature
security cameras with analog video output (black and
white composite video) as an image sensors.
Although it is very cheap technical solution, it brings
couple of disadvantages: it is necessary to use video
grabber in the system and overall characteristics (i.e.
noise parameters, sensitivity and mechanic design) are
matching the price range indeed. Since it is real low-
cost and for example CMOS image sensors are
careless fixed inside case, applicability of this kind of
cameras is very poor especially in applications where
accuracy of imaging system is necessary.
Fig. 3. Arrangement of cameras.
For the transmission of the stereoscopic video
stream were developed custom DirectShow filter.
This filter is virtual capture source with double width
of captured image: left side of image corresponds to
image from the left camera and right side of image
corresponds to image from right camera (see Fig. 4).
It means that on one moment is known where is left
and where is right and no additional synchronization
is not needed. The frame rate of this solution is
limited by USB bandwidth – is between 12 and 15
frames per second while size of images is 640x480
pixels in true colors (it means 24 bits per pixel). JPEG
compression with high quality (low compression) is
used in the basic setup.
Fig. 4. Acoustic transducers on acrylate glasses.
IV. ACOUSTIC TRANSDUCER
In order to design of acoustic transducer suitable
for navigation purposes, device must meet the
following set of requirement, which allow use of the
whole unit in practice:
1) Appropriate scale
Converters are chosen with regard to their weight
and size. It may therefore be a miniature converters
whose frequency characteristic is not ideal due to the
size, but for our purposes will suffice.
2) Appropriate number of transducers
Number of converters is chosen with respect to
their appropriate distribution around the ear. A
suitable compromise appears to be three converters
for the each ear, whose location will be at the front,
back and up.
3) Flexibility of device
The device should be designed a constructed so as
to ensure applicability to more subject on which tests
will be carried out. Since each person has different
sizes and differently shifted ears, it is important that
holder of converters, whose place will be around ears,
made it possible to move in all directions.
4) Correct sound source localization
Correct localization of sound source is tested for
subjective tests using three different audio signals:
Thunder – A signal that begins with short
pulse followed by several smaller pulses.
Spectrum is relatively balanced.
String – A signal, which contains four
pulses slowly declining. Spectrum shows a
slight lift to 4000Hz.
White noise
5) Minimum blocking of ear canal
Blocking of the ear canal was examined as a
secondary product after subjective testing of the
spatial localization of sound source. Signals of
different time waveforms were used, so it was
possible to objectively determine the influence of the
type of audio signal on channel congestion.
V. SUBJECTIVE TESTING
For subjective testing were available three different
audio signals, which simulate the spatial cues. Test
subject (listeners) were placed in an isolated chamber
and had a blank chart, which filled a sense of where
they hear the sound.
Blocking of the ear canal was measured with one
sentence (loudness of 100%, 60% and 20%) and
reference signal. Altogether 10 people attended the
subjective tests. For the evaluation of the success of
localization of surround sound was used localization
coefficient, defined as
It is essentially the average deviation of the estimated
sound direction from the actual sound source. If the
difference is greater than 180°, is necessary to
subtract 360° for maintaining the formula. If the value
of coefficient equal to 1, it is 100% successful
localization. Opposite as long as the value of the
localization coefficient equals to 0, it is largely
unsuccessful localization (the direction of the sound
source is estimated in the opposite direction).
Tab 1: localization coefficient of different sounds
angle
Kthunder
Kstring
Knoise
0°
0.548
0.397
0.409
30°
0.527
0.494
0.600
60°
0.793
0.646
0.683
90°
0.551
0.797
0.613
120°
0.672
0.808
0.625
150°
0.656
0.638
0.683
180°
0.561
0.670
0.689
210°
0.583
0.823
0.550
240°
0.713
0.782
0.822
270°
0.762
0.860
0.767
300°
0.809
0.792
0.759
330°
0.533
0.711
0.569
Values in table are arithmetic mean of estimates of
individual listeners. Apparently the best audio signal
for navigation purposes is sound of string, containing
lot of harmonics. At the same time was measured
blocking of ear canal at different level of loudness.
Measured values (again mean of all listeners) are
stated in Tab. 2.
Tab. 2. Congestion of audio channel
signal
Intelligibility at sound level
100%
60%
20%
thunder
0.725
0.475
0.2
string
0.825
0.625
0.3
noise
0.7
0.45
0.2
Fig. 5. Detail of acoustic transducer
VI. CONCLUSIONS
In this article we presented novel assistive device
for the blind people. Basically system has benefits
from advantages of stereoscopic video (operator in
call centre, who can see environment around blind in
emergency and can perceive depth of space, navigate
user through virtual acoustic beacon) and newly
designed acoustic transducer, which is a crucial part
of our approach: our goal is to minimize load of audio
channel of blind user. Therefore, the sound for
navigation is created outside of ear and blind can hear
ambient noises.
From the subjective tests follows that the most
suitable audio signal for navigation purposes is the
record of string. Also intelligibility of this kind of
signal is favorable. But the problem is right
adjustment of transducer to different shapes of heads
and ears of listeners. Results may be distorted by this
fact.
Further research will be dedicated to optimization
of the transmission of stereoscopic video stream with
very low bandwidth. We would like also test different
configuration of transducers and try to find optimal
solution for right adjustment of transducers.
ACKNOWLEDGMENT
This work has been supported by the research project
MSM 6840770014 “Research of perspective
information and communication technologies” of
MSMT of the Czech Republic. We would like also
acknowledge research project SGS
10/265/OHK3/3T/13 “Modern methods of monitoring
and modelling in acoustic” of Czech Technical
University in Prague.
REFERENCES
[1] World Health Organization, Visual impairment
and blindness (2011-04-12),
http://www.who.int/mediacentre/factsheets/fs282/e
n/
[2] RF guide, Brno, WebProgress, (2011-04-12),
http://www.navigacepronevidome.cz/
[3] Willis S., Helal S., RFID Information Grid for
Blind Navigation and Wayfinding, 9th IEEE
International Symposium on Wearable Computers,
2005.
[4] Baudoin G., Venard O., Uzan G., Rousseau A.,
Benabou A., Paumier A., Cesbron J., The RAMPE
Project: Interactive, Auditive Information System
for the Mobility of Blind People in Public
Transports, Proc. Of the 5th international
conference on ITS Telecommunications ITST
2005, Brest France, June 2005
[5] Navigační centrum SONS ČR, (2011-04-12),
http://www.sons.cz/navigace.php
[6] Farcy, R., Leroux, R., Jucha, A., Damaschini, R,
Grégoire, C., Zogaghi, A., Electronic travel aids
and electronic orientation aids for blind people:
technical, rehabilitation and everyday life points
of view, Conference & Workshop on Assistive
Technologies for People with Vision & Hearing
Impairments Technology for Inclusion CVHI
2006, M.A. Hersh (ed.), 2006.
[7] Sodnik J., Susnik R., Tomazic S., Acoustic signal
localization through the use of Head Related
Transfer Function, Proceeding of international
conference on computer, communication and
control technologies, Florida, July 2003
[8] Virtual acoustic space. (2011-04-12)
http://www.iac.es/proyecto/eavi/english
[9] Klíma M., Systém osobního asistenta pro
nevidomé, PUV 2010-22369, 2010
[10] Wersenyi G., Localization in a HRTF-based
Minimum-Audible-Angle Listening test for GUIB
applications, Electronic Journal Technical
Acoustic, January 2007
[11] Špirk D., Spatial orientation by acoustic
localization, Diploma thesis, Czech Technical
University in Prague, 2011
