Engineering, 2013, 5, 195-198
http://dx.doi.org/10.4236/eng.2013.510B041 Published Online October 2013 (http://www.scirp.org/journal/eng)
Assistive Navigation Device for Visually Impaired —A
Study on Reaction Time to Tactile Modality Stimuli
Jing Yu, Knut Moeller
Institute of Technical Medicine, Furtwangen University, Furtwangen im Schwarzwald, Germany
Received May 2013
ABSTRACT
A tactile system to support severe visually-impaired or blind people in the world for their orientation and navigation had
been developed. To optimize the design, some parameters of tactile display device were evaluated. In the present paper,
we focused on the reaction time to tactile stimuli. In the test, the stimuli were produced through a vibration belt that was
worn around the participants’ waist. In the choice reaction time task, the participants had to click corresponding arrow
keys according to the location of a tactile signal. The findings of this study provided a reference of the reaction time
range, so as to design a more effective and safe tactile navigation system.
Keywords: Tactile Display; Reaction Time; Skin Receptor; Assistiv e Technology; Vibration Belt
1. Introduction
Globally, an estimated 285 million people are visually
impaired, of whom 39 million are blind and 246 million
have low vision [1]. Over the last decades, all kinds of
electronic assistive devices have been proposed for safe
and independent mobility of the visually impaired. The
assistive systems scan the environment (using different
technologies, such as sonar, 3D camera [2]) and display
the information to other senses. The human-machine-
interfaces nowadays not only routinely utilize the audi-
tory stimuli modality, but also increase the use of tactile
modality.
Auditory display is not widely accepted among blind
people, since the sound from voice synthesizers would
conflict with other sounds in the surrounding environ-
ment [3]. The tactile display is more desirable to transmit
the visual information for several reasons. The surface
area of the skin is very large. In addition, tactile displays
provide information in an unobtrusive way [4], and so
this kind of system is suited for users working with other
tasks. Therefore, in our system we chose the sense of
touch to reduce visual information deficiencies for blind
people.
Various forms of assistive devices that can be worn on
different parts of the torso have been developed, such as
finger [5], wrist, forearm [6], tongue [7], feet [8], chest,
belly [9-11] and head [3]. Considering the sensitivity and
adaptability, we developed a belt-type device.
For safety in the navigation task, it is important to
know how far ahead of time a tactile signal should be
sent to the visually impaired people at least. That time
depends on reaction time. Reaction time refers to the
interval of time between the application of a stimulus an d
detection of a response.
Reaction time tasks can be classified according to the
number of diverse stimuli in a task that need to be re-
sponded. When the number of stimuli is equal to one,
this kind of reaction time task is called the simple reac-
tion time task. Simple reaction time task is an issue when
only one particular stimulus can occur or the same re-
sponse is always required. If the number of stimuli is
higher than one, it is defined as choice reaction time task.
This kind of task requires a particular response for each
stimulus [12].
A number of studies have been conducted to analyze
the influence of different factors on human response time
such as stimulus modality, stimulus intensity, gender,
stimulus-response alternatives, and stimulus location [13,
14].
In this paper, a choice reaction test was designed to
investigate reaction time to the tactile stimuli from the
vibration belt.
2. Methods
2.1. Participants
A total of 21 participants aged between 19 and 35 years,
voluntarily took part in this study. All of them were in
good visual, auditory, and physical condition at the time
of the study.

J. YU, K. MOELLER
196
2.2. Hardware
The tactile signals were issued from vibration motors
which were integrated into a simple belt (Figure 1) worn
around the waist. The number and position of the motors
could be adjusted as required.
These vibration motors (model number LA4-432A)
(Figure 2 Left) for the stimulation of the skin receptors
are commercially available by the Nidec Copal Company
(USA) and are mainly used in mobile phones. The size is
16 × 5 × 6 mm. The rated voltage of them is 3 V, the
rated speed 9500 rpm and the rated current 66 A. To as-
sure smooth revolutions, each vibration was packed in a
small plastic tube.
In the test, the vibration motors are controlled with a
NI-USB card (Figure 2 Right) from the National Instru-
ments Corporation (USA). The NI-USB card is con-
nected to the PC with a USB cable. The powe r su pply fo r
the motors was carried out via the voltage output pins of
the NI-USB card. An application program prepared with
C# was used to gener ate tactile stimuli and to ca pture the
participants’ responses. A key board was placed at a
convenient location at the front of the participants and
was used to click the corresponding arrow key.
2.3. Procedure
First, the participants were briefed with the objectives
Figure 1. Prototype of the vibration belt, number and posi-
tion of the motors are adjustable.
Figure 2. Left vibration motor and right NI-USB card.
and procedure of the study. Then they had to wear the
vibration belt with four motors which represented four
directions by their locations. The one near the navel
represented front, the one near the spine represented back,
the one on the left side represented left and the one on
the right side right. Before the tes t, the motors were con-
trolled to vibrate one by one to make sure the participants
could fee l t he vi bration .
The test was a choice reaction time task. The motors
would vibrate 30 times randomly in all different direc-
tions. Each vibration pulse lasted 200 ms. Once the par-
ticipants detected a vibration, they pressed the corres-
ponding arrow key as quickly as possible. After the com-
puter detected the click, another vibration signal would
be generated.
3. Results
A total of 630 responses (21 participants × 30 pulses)
were recorded in the tactile stimuli test. Descriptive sta-
tistics of reaction time were assessed.
3.1. Average Reaction Time and Standard
Deviation
The average reaction time for tactile stimuli was 489 ms
with standard deviation of 142 ms. The average reaction
time and standard deviation for each participant were
plotted in Figure 3 which was sorted by increasing av-
erage reaction time of each participant.
3.2. Position of Vibrators
To evaluate the influence of vibration location, the aver-
Figure 3. The average reaction time and standard deviation
for each participant.
200 400 600 8001000
1
3
5
7
9
11
13
15
17
19
21
Reaction Time (ms)

J. YU, K. MOELLER
197
age reaction time and deviation were plotted in Figure 4.
3.3. Correct and Wrong Response
21 individuals participated in the study; 14 of them made
wrong responses. 630 responses were obtained, out of
which 38 were false reactions. The average reaction time
of correct responses was 490 ms, and the average of
wrong responses was 465ms.
4. Discussion
This study was about reaction time in response to the
tactile stimuli from a vibration belt. Even for the young
age group, the range of reaction time is very wide (Fig-
ure 3). Our design of assistive navigation device aimed
to make the life of visually impaired people more conve-
nient and independent. Since security is a major factor of
such a device, it is important to know how far ahead of
time a tactile signal should be sent at least to allow ap-
propriate actions to be taken by the visually impaired.
According to the results, the tactile sign al should be indi-
vidually adapted and sent between 600 and 900 ms
ahead.
According to the data from different location (Figure
4), the reaction time of left and right is shorter than the
front and back and it might be hypothesized that reaction
time is location specific. Because of the design of key
board, people would like to use index finger to press left
arrow, fourth finger to press right and middle finger to
press up and down. So reaction time might involve long-
er decision time to select and press the appropriate up or
down arrow keys. Further experiments need to be per-
formed to come to a conclusion if left and right sides are
more sensitive than the front and back.
On the average, the reaction time of false responses is
shorter than the correct ones. Since the data of wrong
responses are not enough for a statistical analysis and to
prove significance of differences, further evaluation s will
be performed in the next experimental steps.
For further work, some other factors should be taken
into account too. First, age: the finding that the reaction
time increases with the increase of age has been reported
by Ashoke et al. [15]. With a group of subjects of 5 to 70
Figure 4. The average reaction time and deviation of dif-
ferent locations.
years of age, they found that the response was faster with
an increase of age up to 21 - 25 years and then r esponse-
times gradually increased with age. Second, the com-
plexity of response: Kamitani et al. [16] found that the
response on choice reaction time task was significantly
longer than simple reaction time task. According to this
study, the possible explanation of such finding was that
choice reaction task required not only stimulus percep-
tion and execution of the response but also decision-
making processes.
Overall, even the combination of the effects of differ-
ent factors should be considered in future study. The
present finding is still a useful reference to design a safe
tactile navigation system for visua lly impaired.
5. Acknowledgements
This work was supported by the Bundesministerium für
Bildung und Forschung (BMBF), IH-2 iVIEW, FKZ
13EZ1129A.
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