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INVITED PAPER

Special Section on Electronic Displays

A Study on the Increase of Perceivable Information in the Saccadewith High Speed Line Display
Naoki KAWASAKI†a) , Member, Yuuki MACHIDA† , Takayuki MISU† , Nonmembers, Keiichi ABE† , Member,
Hiroshi SUGIMURA† , Nonmember, and Makiko OKUMURA† , Member

SUMMARY
A line display that utilizes saccade has been proposed.
When an observer moves his or her eyes on a one-dimensional fixed line
display, two-dimensional information is perceived on the retina. In this paper, a high speed flashing line display was developed using a CPLD and
PIC microcontroller. The flashing period was reduced to 20 μs, which wasless than half that of our previous system. The relationship between the
flashing frequency and the optimum distance that can be perceived with theleast distortion was clarified. The results show that the higher the flashingfrequency is, the more information can be perceived from a farther position. Calculated values, which were based on the relationship between the
flashing period and the width of the light source, were almost identical withmeasured values at the flashing frequencies from 3.3 kHz to 10 kHz. Due toshort flashing period, the developed line display not only was visible at distance of 15 m or more, which is suitable for outdoor use, but also realized
16 gray levels.
key words: saccade, line display, flashing frequency, perceivable pixels

1.

Introduction

We frequently move our eyes to the object of interest in ourlives. The fast eye movement occurring at this time is calleda saccade [1]. A line display using this saccade has been
proposed [2], [3]. When an observer moves his or her eyes
across a one fixed dimensional line display, a series of linear
images produced by vertically dividing an image to be displayed are sequentially flashed at high speed, whereby thetwo-dimensional information is perceived on the retina by
the eyeball movement and the flashing vertical pattern appears to be expanded horizontally. On the other hand, thetechnology called persistent of vision (POV) or versa-writer
has been used for a long time as a method of presenting
two-dimensional information by using the after-image fromthe fixed one-dimensional flashing point sequences. In thiscase, a large space and high power are required to move thedevice, but in the case of a line display, the human retina
perceives the after-image on a single line. Therefore, thissystem can display information without moving the device,
and is expected to be useful for nighttime advertisements
and lighting for entertainment, such as illumination.
An earlier study reported on the temporal relationshipbetween the size of the perceived image and eyeball movements in a similar device [4]. In Ref. [5], a method ofManuscript received February 26, 2021.
Manuscript revised June 2, 2021.
Manuscript publicized August 17, 2021.
†
The authors are with Kanagawa Institute of Technology,
Atsugi-shi, 243–0292 Japan.
a) E-mail: kawasaki20@ele.kanagawa-it.ac.jp
DOI: 10.1587/transele.2021DII0001

creating content images based on perceptual characteristics
by saccades was proposed, in which the flashing frequencyof the device was set to 2 kHz. We have been studying anddeveloping line displays, and our previous studies have clarified the relationship between the flashing period of one line
and the angle of eyeball movements [6]. We also developed
a line display driving 64 LEDs and conducted experiments
to evaluate the size of the image for the flashing period using
saccade [7]. With respect to grayscale of displayed images,
a 5 gradations image was displayed by the fastest flashing
period of 42 μs [8]. In the previous experiments, the distance between the device and the subject was fixed at 2 to
3 m for domestic use. However, it is required to be visible from a larger distance for outdoors use at night such as
advertising.
In this paper, we have developed a fast flashing line
display with 20 μs, and by varying the distance between
the subject and the display, we have clarified the relationship between the distance and the flashing frequency thatcan be perceived with no visible distortion. We have also
verified that the number of pixels and color gradation can beincreased with the high speed flashing [9].
2.

Principle of Line Display Using Saccades

The principle of the line display is shown in Fig. 1. Whena string of light dots is moved at faster than a certain speed,
the trajectory is perceived as a continuous line due to the afterimage. On the other hand, when the eye moves at fasterthan a certain speed, a similar phenomenon happens. A
line display is used to present information by changing theemission pattern of a fixed string of light dots, using themislocalization caused by the saccade of the eyeball that

Fig. 1

Perceptual of line display.

c 2022 The Institute of Electronics, Information and Communication Engineers
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catches it [5], [10]. In addition, the image is perceived as
the reversed of the pattern of the issuing optical point sequence [11]–[14]. Typically, the rotational speed of a saccade is 300-500 deg/s with a duration of 30 - 50 ms [15]. The
maximum speed of the saccade varies with amplitude, from
250 deg/s for 5 deg to 650 deg/s for 20 deg [16]. Similarly,
the saccade duration also increases with amplitude, and theduration T of the saccade increases with amplitude A. The
relationship is approximated by the following Eq. (1).
T = T0 + d · A(1)

T 0 is 20 - 30 ms, and d is the amount of increase per deg of
amplitude, which is about 2-3 ms [17]. However, the maximum speed and duration of the saccades were slightly diﬀerent among research results [18]–[22], which may be causedby measurement methods and individual diﬀerences [15].
The saccades used here are high-speed eye movements thatcatch up with the object captured in the peripheral vision,and can move the gaze at extremely high speed, but during
the movement, saccade suppression occurs and the visibility
characteristics decrease [1]. In general, saccade suppression
begins several tens of milliseconds before the onset of thesaccade, reaches its maximum during the saccade, and continues after the saccade ends [23]–[25]. However, saccade
suppression is less likely to occur in the case of stimuli that
contain many high spatial frequency components [26]–[29].
In addition, the darker the background is the more suppression occurs [2], [30], [31]. Therefore, it is preferable to use
the system in dark environments such as dark rooms or outdoors at night.
3.

was designed to enable the connection of five or more subboards using a comparator. Figure 3 shows the sub-board
configuration and Fig. 4 shows the timing diagram. The datatransferred in 8 pixels divided into 24 times is held in thelatch circuit, and after all the data is completely transmitted, it is sent to the transistor arrays all at the same time.
The latch circuit that holds the data, the comparator for selecting the sub-board and the decoder were designed using
the CPLD. The PIC24EP512GP204 is used as the microcontroller. The pattern diagram of the sub board designed
by CDA software Eagle and the developed sub-board areshown in Fig. 5. The board was 122 mm long (16 LEDs)
and 100 mm wide. Connect the microcontroller board andthe sub board as shown in Fig. 6. A developed line display
with four sub-boards and a microcontroller board is shownin Fig. 7. Figure 8 shows the result of measuring the fastest
flashing period with an oscilloscope. The fastest flashing period is 20 μs, which is more than twice as fast as the device
developed in our previous work (42 μs) [8].
4.

Increase in the Number of Shades Due to High Speed

A PWM waveform is generated to create multiple gradations. Assuming a flashing period T and a data transfer timeof td , the gradation G = T/td + 1, therefore, if the data

Development of High Speed Flashing Line Display

In this paper, a line display is created using a complex programmable logic device (CPLD) and a PIC microcontroller
in order to shorten the data transfer time. It consists of a microcontroller board that transfers data and four sub-boards,
where each sub-board drives 16 LEDs, as shown in Fig. 2. It

Fig. 3Fig. 2

Configuration diagram of the sub board.

Configuration diagram of line display.

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Fig. 4

Timing diagram of data transfer for LEDs.

Fig. 5 Pattern diagram designed by CDA software Eagle and the developed sub-board.
Fig. 7

Fig. 6

Connected the microcontroller board to the sub board.

Fig. 8Developed high speed line display.

Observation results by the oscilloscope.

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Fig. 9Displayed gray scale images by our developed line display.

transfer time is 20 μs and the most visible flashing period
is 0.3 ms [8], the gradation can be increased to 16 levels.
The 16 levels pixel value was determined by Eq. (2), whichtransforms the usual linear 256 levels pixel value E into an
exponential 16 levels pixel value R, taking into account ofperceptual sensitivity based on the Weber-Fechner law.
 α
E
(2)
R = 255
15
In an experiment on image visibility considering perceptual
sensitivity using a line display, it was confirmed that visibility was improved by correcting the perceptual sensitivity [32]. α is the correction value, which was set to 1.7. Face
images with multi-leveled colors of 5 and 16 displayed bya flashing line display are shown in Fig. 9. This picture wastaken by moving a digital camera to simulate eyeball movements. By increasing the number of grayscales, the imageof the face is displayed more clearly.
5.

Experiment

The experiment was conducted to evaluate the flashing period and perceivable distance of images. The experimental
condition is shown in Fig. 10. The experimental environment was outdoor at night, the illumination was 0.9 lx, anda 64x64 pixels yellow star image. The evaluation criteria
for image perception are shown in Fig. 11. Four subjects(S0-S3) were tested to measure the distance L, which is the
optimum distance to perceive the displayed image with theleast distortion, at each flashing period. The experiments
were conducted with a flashing period ranging from 0.05 ms(20 kHz) to 0.3 ms (3.3 kHz). A photograph taken by moving a digital camera in the same way as the eye movement
when the line display was actually operated to output theimage used in the experiment is shown in Fig. 12.
6.

Fig. 10

Experimental condition for optimal distance.

Fig. 11

The evaluation criteria for image perception.

Fig. 12The images used in the experiment captured by a digital camera.

Fig. 13tance.

The relationship between flashing frequency and optimal dis-Results

The measurement results of the four subjects (S0-S3) andtheir average values are shown in Fig. 13 and Table 1. Agraph of the mean and standard deviation of the measurements from the results is shown in Fig. 14. The verticalaxis is the perceptible distance and the horizontal axis is the
flashing frequency. The results showed that the optimal distance for perception was longer as the flashing frequency
was higher, and shorter as the frequency was lower. Whenthe flashing frequency was 20 kHz, the maximum and minimum values were 19.1 m and 11.4 m, respectively, and theaverage value was 15 m. As the flashing period was decreased, the visible distances became shorter, with a maximum of 4.0 m, a minimum of 2.6 m, and an average of 3.3 m
at 3.3 kHz. Figure 14 shows that the standard deviation increases as the flashing frequency increases.

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Table 1 The measurement results of the four subjects (S0-S3) and theiraverage values.

Fig. 15

Optimal distance and measured values on flashing frequency.

Fig. 14 The average and standard deviation of the relationship between
flashing frequency and optimal distance.

7.

Discussion

According to Ref. [2], when the saccade amplitude is θ deg
and the width of the light source in the field of view is D deg(for example, D = 0.1 deg for an LED with a light sourceof 5 mm observed from 3 m away), the maximum numberof horizontal pixels X that can be displayed is given by thefollowing equation.
X = θ/D(3)

Let  be the distance the light source moves on the retina
during the flashing period tm , then = V × tm

(4)

Where V is the eye velocity in saccades. When the moving
distance on the retina  is larger than or equal to the widthof the light source D (D  ), the lights can be perceived
without overlapping, and particularly when the width is thesame as the light source (D = ), the information can beperceived without distortion. When θ is constant, the maximum number of pixels X depends on D. When V and tm areconstant, D is relevant for presenting information with lessdistortion. The width of the light source D is given by thefollowing equation.
D = tan−1 (h/L)(5)

where h is the LED size and L is the optimal distance between the device and the subject. From Eqs. (4) and (5), assuming a velocity V, we have calculated the optimal visual
distance L for each flashing period at D = , and compared
it with the average of the measured values. Optimal distance and measured values on flashing frequency are shown

Fig. 16

Perceivable pixels depending on flashing frequency.

in Fig. 15.
In daily life, saccades of around 10 deg are common [14]. The maximum speed of a saccade at an angleof 10 deg is 400 deg/s [16]. Assuming that the angle ofthe eye moved by the subject is 10 deg and the speed is
400 deg/s, we calculated the optimal distance at which theimage can be perceived. Comparing the measured values inFig. 15 with the calculations, the two are close at distances
shorter than 12 m, but the measured values are saturated at
distances longer than 12 m, and the diﬀerence from the calculated values increases. This is thought to be because thevisual acuity deteriorates as the distance between the subject
and the display increases, so that the optimum perceptual
distance is saturated due to the limitation of visual acuity.
Figure 16 shows the result of calculating the maximum number of pixels for each flashing frequency from Eq. (3) using
the optimum distance for each flashing frequency in the experimental results. It shows that the number of perceivable
pixels increased as the distance and the flashing frequency
increased.
8.

Conclusions

In this paper, a high speed flashing line display was developed using a CPLD and PIC microcontroller. The flashing
period was reduced to 20 μs, which was less than half that ofour previous system. The relationship between the flashingfrequency and the optimum distance that can be perceived

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with the least distortion was clarified. The results show thatthe higher the flashing frequency is, the more information
can be perceived from a farther position. Calculated values,
which were based on the relationship between the flashing
period and the width of the light source, were almost identical with measured values at the flashing frequencies from
3.3 kHz to 10 kHz. Due to short flashing period, the developed line display not only was visible at distance of 15 m or
more, which is suitable for outdoor use, but also realized 16
gray levels.
Acknowledgments
We would like to express our sincere gratitude to Mr.
Tetsuya Gokan, President of Microchip Design Lab, Inc.
for his useful advice. We would like to thank Dr. Yoichi
Yamazaki for his cooperation. In this paper was supported
by JSPS Research Grant JP18K04170.
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Naoki Kawasaki
received the B.E. and M.S.
degrees in Electrical and electronics Engineering from Kanagawa Institute of Technology in2020 and 2022, respectively. He has studied display technologies.

Yuuki Machidareceived the B.E. and M.S.
degrees in Electrical and electronics Engineering from Kanagawa Institute of Technology in2019 and 2021, respectively. He has studied display technologies.

Takayuki Misu
received the Ph.D. in Engineering from Kanagawa Institute of Technology
in 2008. He has been a professor of the Faculty of Creative Engineering, Kanagawa Institute of Technology since 2020. His research interests include the Application of LED. He is amember of the Illuminating Engineering Institute of Japan, and the Japan Society of Applied
Physics.

Keiichi Abe
received a Ph. D. in informatics from Shizuoka University in 2012. He
has been an professor of the Faculty of Creative
Engineering, Kanagawa Institute of Technology
since 2020. His research interests include smart
system using IOT technology, Interactive system using Robot and CG, and Victims Information Management System at Large Scale Disaster, HEMS. He is a member of Information Processing Society of Japan, the institute of Electronics, Information and Communication Engineers of Japan and a member of IEEE.

Hiroshi Sugimura
Doctor of Engineering. Associate Professor. Department of Home
Electronics, Faculty of Creative Engineering,
Kanagawa Institute of Technology since 2016.
And also he has been Department of Electricaland Electronic Engineering, Graduate School ofEngineering, Kanagawa Institute of Technology,
JAPAN.

Makiko Okumura
received her B.E. degreefrom Keio University in 1982, and Ph.D. degree
in electrical engineering from Tohoku University in 1994. She joined Toshiba R & D Center,
Kawasaki, Japan, and transferred to Kanagawa
Institute of Technology in 2000. She has beenworking on the development of analog circuit
simulators and now studying consumer electronics. She is a member of the institute of Electronics, Information and Communication Engineersof Japan and a member of IEEE.