RELATIONSHIP BETWEEN THERMAL PERCEPTION AND

MECHANICAL CHARACTERISTICS ON A PALM

Aiming at Developing a Communication Support Device for the Deaf-Blind

Chikamune Wada, Kuranosuke Sako and Hiroshi Horio

Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Hibikino 2-4

Wakamatsu, Kitakyushu, Japan

Keywords: Deaf-blind, tactile display, mechanical characteristics, thermal perception.

Abstract: Our final goal is to develop a portable display which will enable the deaf-blind to character on the palm

through the use of tactile sensations. We propose the use of thermal stimulation as the tactile sensation,

because in this way small-sized and lightweight devices can be developed. However, it might still be

impossible to capture continuous movement, which is necessary to recreate characters on the palm. In past

research, we found that thermal perception is dependent on the palm position. Therefore, in this study, we

investigated the cause of this position dependence by comparing the skin’s thermal perception and its

mechanical characteristics.

1 INTRODUCTION

Since the deaf-blind suffer from both visual and

auditory impairment, it is easy to understand the

communication difficulties that arise due to this

affliction.

In this research, we tried to create a device that

can facilitate effective communication among the

deaf-blind and the non-disabled.

Since schools throughout Japan teach both the

deaf and the blind to write phonetic symbols known

as “kana,” most Japanese deaf-blind are familiar

with this standard Japanese writing system. Then,

some deaf-blind use a communication method which

is writing characters on the palm of their hand using

a finger. Therefore, we thought this could provide

the basis for a communication device that can be

used among deaf-blind.

Generally speaking, a person's finger moves

continuously when a kana is written on the palm.

Needless to say, it will be easy to transmit a shape of

kana by using a kind of pin tactile display for the

blind (Itoh, Sakai and Sakajiri, 2003). However, we

think the stroke order of writing kana is important to

let the deaf-blind know kana. Then, our goal is to

develop a portable display which enables a person to

write kana on the palm through the use of tactile

sensations (Wada and Wada, 2003.). Although this

finger movement can be reproduced by using a XY-

stage, it is not possible to carry such a stage because

of its size and weight. To resolve this drawback, we

surmised that a portable display can be realized by

making use of a Peltier element, which is both small

and light. However, even if the elements were

arranged, it might still be impossible to recreate

continuous movement of tactile stimulation on the

palm. Instead, we supposed that continuous

movement can be realized using the apparent motion

phenomenon.

In previous research (Horio and Wada, 2005), we

investigated the optimal condition under which

thermal stimulation of a Peltier element causes

apparent motion. However, some subjects could not

perceive the apparent motion. We hypothesized that

this was due to the individual differences in the

characteristics of thermal stimulation reception.

Incidentally, it was difficult to measure the thermal

stimulation reception while it was easy to measure

mechanical characteristics of skin. Therefore, we

would like to make a model by which thermal

stimulation perception will be able to be estimated

by mechanical characteristics.

In this study, we chose response time to cold

sensation and mechanical impedance as a parameter

of thermal stimulation perception and mechanical

characteristics, respectively. Then, we investigated a

relationship between the response time and

mechanical impedance.

307

Wada C., Sako K. and Horio H. (2008).

RELATIONSHIP BETWEEN THERMAL PERCEPTION AND MECHANICAL CHARACTERISTICS ON A PALM - Aiming at Developing a Communication

Support Device for the Deaf-Blind.

In Proceedings of the First International Conference on Bio-inspired Systems and Signal Processing, pages 307-310

DOI: 10.5220/0001070103070310

 SciTePress

2 MEASUREMENT OF

RESPONSE TIME

2.1 Experimental Setup

Figure 1 illustrates the outline of our experimental

setup. Peltier elements (8.3 mm*8.3 mm*2.4 mm)

were used to induce thermal stimulation. These

elements were connected to a computer through a

D/A converter and an amplifier. The thermal

stimulation was controlled by the computer. Two

thermocouples were used to measure the

temperature: one was attached to the Peltier element

to measure its temperature, while the other was

attached to the palm to measure the skin surface

temperature. The thermal data from the

thermocouples was directly inputted into the

computer through an A/D converter.

2.2 Experimental Procedure

The right palm was thermally stimulated. The palm

length and hand breadth were measured, and the

palm was divided into 16 parts (Fig. 2). The

assigned number and alphabet indicates the place

where thermal stimulation was induced. Figure 3

shows the thermal stimulation pattern. The vertical

axis indicates the temperature of the Peltier element,

while the horizontal axis indicates the elapsed time.

Before the start of the experiment, the temperature

of the Peltier element was adjusted to the same

temperature as the subject's skin surface. The

environment temperature was between 25 and 28

degrees Celsius. The subjects were six males, 22 to

25 years of age. The trial was repeated 10 times for

each subject. The subjects wore earplugs and

eyeshades in order not to hear environmental noise

and see.

When the Peltier element surface reached the same

temperature as the palmar skin surface, the element

was placed on the palm. After a while, the

temperature of the Peltier element decreased. The

ratio of temperature decrease of the Peltier element

was -5.5 degrees Celsius per second.

The subjects were asked to push a switch when

they felt that the Peltier element had become cold

(“Stop” in Fig. 3), after the temperature of the Peltier

element started to decrease (“Start” in Fig. 3). The

time interval between “Start” and “Stop” was

measured. This time interval was named the

“Response time.”

Figure 2: Stimulation points.

2.3 Results and Discussion

Figure 4 shows the average results for all subjects.

The vertical axis shows the response time in seconds

while the horizontal axis shows the stimulation

points.

As Figure 4 shows, the response time was different

for each stimulation point and about 1 second. Next,

we calculated the deviation value for all response

time in order to standardize the data. Table 1 shows

the results for the deviation value of response time.

When the response time was mean, the standardized

Figure 3: Stimulation pattern.

Temperature

Time

Sto

Star

Response time

DA AMP

Figure 1: Experimental setup.

Peltier element

Thermocouples

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value was 50. If the value was larger than 50, it

meant the response time was longer than the mean

and vice versa.

Figure 4: The response time.

Table 1: Standardized response time.

a 47.938.234.740.7

b 53.738.641.140.3

c 44.445.645.253.3

42.

36.5

38.6

40.5

41.1

43.6

45.2

46.8

53.3

53.6

Figure 5: The standardized response time in contour graph.

Figure 5 shows the contour graph of standardized

response time. From figure 5, it was found that the

response time was short on position “a” and central

area of palm. And it was also found that the response

time was long on peripheral area of palm.

3 MEASUREMENT OF

MECHANICAL IMPEDANCE

3.1 Experimental Procedure

The palmar mechanical impedance can be found

from the power and the acceleration caused when

the palm is vibrated at various frequencies.

Therefore, we devised an experimental setup capable

of inducing the vibration of the skin. We used a

small vibrator, and measured the power and

acceleration by means of an impedance head. The

mechanical impedance of the skin was measured

with the measurement setup shown in Figure 6. The

vibrator outputted a sine wave vibration, and the

vibration was relayed to the palm through the

impedance head and the contactor pin. We used 15

measurement frequencies: 80, 100, 150, 200, 250,

300, 350, 400, 450, 500, 600, 700, 800, 900 and

1000 Hz. A touch sensor was used to confirm that

the palm touched the contactor pin. The same

subjects in chapter 2 participated in this experiment.

The subjects touched the pin with the palm of the

right hand. When the pin touched the palm, the

vibrator made the skin vibrate. The subjects were

asked to control the pressure of their palm on the

contactor pin by watching the output of the load cell.

The power with which the skin pushed the pin was

set to 50 gf. During the experiment, the subjects

were asked to simply place their palm onto the

contactor pin. The impedance of the palm was

measured by the impedance head, and the data were

inputted into a computer. The measurement was

made as described in chapter 2 (Fig. 2).

Figure 6: Mechanical impedance measurement device.

3.2 Results and Discussion

From the analyses of mechanical impedance, we

divided them into two categories. The typical

patterns of each category were shown in Figures 7

and 8. Figures 7 and 8 show the average results for

all subjects at stimulation point a2 and d2,

respectively. The vertical axis shows the impedance.

The horizontal axis shows the frequency in Hz. The

lower part of those graphs shows the imaginary part

Impedance head

Contacto

Oscillato

Amp

Vibrato

Load cell

Oscilloscope

Static force

Touch senso

Force, Acceleration

RELATIONSHIP BETWEEN THERMAL PERCEPTION AND MECHANICAL CHARACTERISTICS ON A PALM -

Aiming at Developing a Communication Support Device for the Deaf-Blind

309

of the impedance. The upper part shows the real part

of the impedance.

Figure 7 shows that the value of imaginary part

increased as the frequency increased. We called this

pattern #1. On the other hand, the value of imaginary

part increased and decreased as the frequency

increased in figure 8. We called this pattern #2.

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Re A

Im A

Re B

Im B

Re C

Im C

Re D

Im D

Re E

Im E

Re F

Im F

Fr e

uenc

[

]

Figure 7: The impedance change (pattern #1).

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

Re A

Im A

Re B

Im B

Re C

Im C

Re D

Im D

Re E

Im E

Re F

Im F

Fr e

uenc

[

]

Figure 8: The impedance change (pattern #2).

Table 2 shows the categorized results for all

stimulation points. One-asterisk shows that pattern

#1 change was obtained in the stimulation point,

while two-asterisks shows pattern #2. From table 2,

it was found that the pattern #2 was obtained on

peripheral palm where the hand was relatively thick

and the pattern #1 was obtained on relatively thin

part.

Table 2: Position dependence of impedance change.

3.3 Comparison between Response

Time and Mechanical Impedance

Figure 9 shows the combination between figure 5

and table 2. From figure 9, it was found the response

time was relatively short at the area of pattern #1,

while the response time was relatively long at the

area of pattern #2. There seemed to be a relationship

between response time and mechanical impedance.

Therefore, we hypothesized that the response time

could be obtained by using mechanical impedance.

36.5

38.6

40.5

41.1

43.6

45.2

46.8

53.3

53.6

1234

Pattern #1

Pattern #

Figure 9: Comparison between response time and

mechanical impedance.

4 CONCLUSION

We investigated the relationship between response

time and mechanical impedance in this paper. In the

near future, we are planning to make an energy

conductive model by using mechanical

characteristics in order to estimate thermal

stimulation response.

REFERENCES

Horio, H., & Wada, C., 2005. Basic research into the

development a Deaf-Blind communication device

based on the use of thermal apparent motion, SICE

Annual conference 2005, 348-352.

Itoh, K., Sakai, T., & Sakajiri, M., 2003. Assistive

technology in the use of a PC for the deaf-blind(In

Japanese), WIT 2002 of the Institute of Electronics,

Information and Communication Engineers, 25-28.

Wada, C., & Wada, Y., 2003. A proposal for a

communication device with a finger and a palm for the

deaf-blind, 10th International Conference on Human -

Computer Interaction, 4, 281-285.

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