Assistive Navigation Device for Visually Impaired—A Study on Reaction Time to Tactile Modality Stimuli

doi:10.4236/eng.2013.510B041

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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

Email: [email protected]

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

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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