Systems and Computers in Japan, Vol. 36, No. 9, 2005
Translated from Denshi Joho Tsushin Gakkai Ronbunshi, Vol. J86-D-II, No. 9, September 2003, pp. 1350–1357

Time Course of Localization for a Repeatedly Flashing Stimulus
Presented at Perisaccadic Timing
Junji Watanabe,1 Taro Maeda,2 and Susumu Tachi1
1Graduate School of Information Science and Technology, The University of Tokyo, Tokyo, 113-8656 Japan
2

NTT Communication Science Laboratories, NTT Corporation, Atsugi, 243-0198 JapanSUMMARY

1. Introduction
In visual information presentation methods with twodimensional spread, the scanning process, such as a CRT
display, in which the information is presented by moving alight spot at high speed has mostly been used. There is alsoa device, as shown in the left panel of Fig. 1, in which aphysical motion is performed and the two-dimensional
information is presented by using light spots in a row.
On the other hand, the following phenomenon exists.
Light spots are fixed in a row. When the flashing pattern ischanged at high speed while the observer is in saccade, theflashing pattern is expanded into a spatial pattern by the eye
movement, and a two-dimensional image is perceived. It isthus possible to present information efficiently with little

When a light spot is flashed repeatedly during saccade, a dotted line called a phantom array (PA) is perceived.
When light spots are placed on a vertical line and the
flashing pattern is changed quickly during saccade, theflashing pattern is expanded to a spatial pattern by the effectof eye movement, and a two-dimensional image is perceived. The authors have proposed a visual information
presentation method based on this phenomenon. A crucial
issue in information presentation by this method is the time
relation between the perceived PA and the eye movement.
Consequently, this study examines the time relation between the perception and the eye movement. The timecourse of perceived position for repeatedly flashing stimulus is investigated by presenting light spots in the vertical
position. It is found that the locus of the perceived light spot
starts to curve at the start of saccade in the direction opposite to the saccade, and returns to the vertical direction when
the saccade ends. It differs from the locus of the light spot
which is expected in accordance with cancellation theory.
© 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 36(9):77–86, 2005; Published online in Wiley InterScience(www.interscience.wiley.com). DOI 10.1002/scj.10690

Fig. 1. Information display device based on moving
light array and based on eye movement.

Key words: saccade; display; spatial localization
error; cancellation theory; phantom array.

© 2005 Wiley Periodicals, Inc.
77

space and energy without moving the light spot itself, but
by using eye movement, as in the right panel of Fig. 1. The
authors have been proposing a visual information presentation method (saccade-based display, SD) based on thisprinciple [1].
The perception characteristics differ between the saccade state and the gaze state. Consequently, the design
theory for SD must be composed on the basis of the perception characteristics during saccade. There has been a reportin which a light spot is repeatedly flashed during saccadeand the direction of motion of the light spot is reported, in
an attempt to analyze the time course relation between thelight spot perception position and the eye movement [2].
However, the subjective perception of the directionof motion of the light spot includes individual differences.
It will also be affected by uncontrollable factors such as theattention of the observer [3]. Consequently, in this study,
the light spot stimulus is flashed in the vertical direction sothat the time course of the light spot perception position isplaced by the vertical position, in an attempt to analyze thetime course relation between the perception of the repeatedly flashing light spot and the eye movement without
utilizing subjective report.

reported that information such as characters can be perceived during saccade [6].
2.2. Perception of light spot withinstantaneous presentation
In connection with light spot perception characteristics during saccade, Honda presented a study of theerror of spatial localization [7, 8]. Spatial localization error
refers to the phenomenon in which, when a flash light spot
is presented during saccade, its position is localized with anerror that has a certain tendency. Figure 2 shows the conceptof the phenomenon, in which the magnitude of the localization error is the vertical axis, and the time (ms) is thehorizontal axis. The solid line represents the eye position,and the dotted line is the time course of the localization error
magnitude.
Generally, when the light spot is presented before
saccade, the localization error is in the same direction as thesaccade. If it is presented during the saccade, the error
localization gradually changes. When it is presented after
the saccade, the localization error is in the opposite direction to the saccade. The absolute localization error is maximized if the presentation is near the start or end of thesaccade. This phenomenon can be accounted for by thecancellation theory between the internal information of eye
position and the retinal information [8].

2. Spatial Perception Characteristics
during Saccade
This section outlines the visual information presentation method utilizing saccade. The relation between thisstudy and past studies concerning the light spot perception
in saccade is discussed.

2.3. Perception of repeatedly flashing lightspot
Hershberger reported the following phenomenon.
When a light spot is repeatedly flashed during saccade at afrequency of 120 Hz, a dotted line is perceived, appearing
successively in the opposite direction to the saccade, as
shown in Fig. 3 [9]. This is called a phantom array (PA).

2.1. Visual information presentation method
based on saccade
In SD the information is presented as follows. The
eye movement of the observer is not measured. By flashing
the light spot as the target of saccade, the information
provider tries to induce saccade (with a maximum movement velocity of 300 to 500°/s [4]). Then, by flashing thelight spot according to the saccade, the information isdisplayed [1]. For reliable information presentation, thelight spot row is flashed at high speed from 100 ms before
to 100 ms after the saccade.
It is generally suggested that perception is suppressed
during saccade and that the resolution of perception isdegraded. There is also a report, however, that the suppression is smaller for stimuli with a high spatial frequency, as
presented in SD [5]. In fact, it has been verified that when
the background intensity is low and the contrast of thestimulus with the background is sufficient, there is little
degradation of visual resolution [1]. Fujita and Amami

Fig. 2. Time course of mislocalization before, during,
and after a saccade.

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reported that the perceived PA has approximately half thesize of the eye movement [10]. Essentially, it is interpreted
that the two-dimensional image perceived by SD is equivalent to the vertical arrangement of PA.

3. Time Relation between PA Perception
and Eye Movement
Fig. 3. Perception of phantom array.
In order to determine the flash timing of the light spot
array in the information presentation based on SD, it is
crucial to know the time relation between PA and eye
movement. In the experiment by Hershberger’s group, thelight spot is repeatedly flashed only during saccade. They
do not discuss the time relation between the perceived PA
and the eye movement. Consequently, the light spot is
flashed in perisaccadic period in this study, and the time
relation between the perception and the eye movement is
examined by a psychophysical experiment.

If the perceived locus for the repeatedly flashing lightspot is the curve that is obtained by connecting the perceived position for the flash light spots, as shown in Fig. 2,
the PA should be moved to the same direction as the saccade
immediately before and after the saccade. Such a subjective
perception, however, has not been reported in the experiments in this paper, or in the study by Hershberger andcolleagues [9, 10].

3.1. Procedure of experiment2.4. Features of image perceived by SD

The fixation point (FP), the target point (TP), and thelight spot (S) are placed as shown on the left side of Fig. 5.
Sixty-four LEDs are arranged vertically as S. S is placed at
the center between FP and TP. The distance between theright eye of the subject and S is set as 150 cm and the
distance between FP and TP is set as 8° or 12° in terms ofthe view angle. The height of FP, TP, and the center of S are
set at the same height as the eyes of the subject.
The right side of Fig. 5 shows the time chart of theexperiment. As the first step, FP is flashed at random for 1
to 2 s, and the subject looks toward FP. Then, FP is left off.
After 200 ms, TP is on for 10 ms. The subject performs ahorizontal saccade toward TP. In the process, after 62 ms
from TP being off, S is flashed successively from the top.
The flash is 2 ms per spot, or 128 ms in all (throughout this128-ms period, only one of LEDs is on). The gap of 200 ms
is set in order to induce the express saccade, in which the

The image perceived by SD differs from the image
on the retina generated by eye movement in terms of sizeand position. Specifically, the image perceived by a saccadeof 10° differs from the image of 10° projected on the retina
as in Fig. 4. Its size is approximately 5°, which is approximately half the retinal image as in the lower side of Fig. 4(it sometimes happens, as in the figure, that the perceived
image covers the light spot array). Hershberger’s group also

Fig. 4. Retinal image (top) and perceived image(bottom).

Fig. 5. Outline of the experiment and time chart.

79latency is especially stable in time [11], so that stable
experimental conditions are realized.
The locus of the light spot which is perceived by the
subject in saccade, always has the shape of the sigmoid
function, which is interpreted as a result of vertical expansion with the time axis of PA as on the left of Fig. 6. In theexperiment, the eye movement of the subject is measured.
The subject is also instructed to indicate with a laser pointerthe “start point,” where the perceived light spot locus starts
to curve in the horizontal direction, and the “end point,”
where the locus returns to the straight line (cross on the leftof Fig. 6). The indicated position is recorded on a section
plane containing the focus point, target, and light spot array.
The position is read on the basis of the light of the pointer.
The read value is not reported to the subject.
The start and the end of the flashing light spot array
were measured in parallel to the eye movement. Based onthese records, the time relation between the period forwhich the light spot was on at the position reported by the
subject and the onset/offset of the saccade can be determined. In the experiment, the magnitude of the saccade is
set in two ways, as 8° and 12°.

were four men in their twenties who had visual acuities ofat least 0.6 with correction.
3.3. Preliminary experiment
In this experiment, the light spot array was flashedsuccessively from the top to the bottom so that the timecourse of the PA spread in the horizontal direction in space
was expanded into a change in the vertical direction, andthe time relation to the eye movement was examined. Whatis important in this process is that the time relation in thehorizontal movement to repeatedly flashed spot lightshould be the same as the time relation to the case in which
the spots are flashed sequentially from the top. In order tocheck the agreement of the time course, the following
preliminary experiment was performed.
The same LED (S*) as was used in S was placed
immediately above the top LED of the light spot sequence
S, and was flashed for the same period as S was flashed. S
was flashed sequentially from the top, each LED for 2 ms,
and S* was repeatedly flashed on and off for 2 ms. If bothends of S and S* always coincided, it was judged that thetime courses of S and S* in the horizontal direction were
the same. While turning S and S* on in various timings inperisaccade for on-times of 32, 64, 96, and 128 ms, thesubject was instructed to observe the deviation at both ends.
The results show that all subjects perceived that bothends of S and S* agreed. Consequently, it is considered inthis experiment that the time course of PA in the horizontal
direction was expanded by S in the vertical direction.

3.2. Experimental device
A red LED (diameter 0.25° and 60 cd/m2) was used
for the fixation point (FP) and the target point (TP). A green
LED (diameter 0.2° and 20 cd/m2) was used for the repeatedly flashing light spot array (S). The vertical length of S
was 12.8°. A PIC16F877 single-chip microprocessor wasused for the flashing control of the LED. The subject
covered the left eye using the eye-band and indicated thestart and end points of the perceived light spot locus. The
head of the subject was fixed on the chin rest. The eye
movement was measured with 600-Hz sampling, using an
EMR-600 produced by NAC Co. The experiment was
conducted in a completely dark room (0.01 lx). The subjects

3.4. Data processing
For each of the subjects, data for the express saccadewith small latency variation, consisting of 20 trials in eachset, were obtained, except for the following cases. In trialsof 8°, the case in which the saccade amplitude was below
6° or above 10° was excluded. In trials of 12°, the case inwhich the saccade amplitude was below 9° or above 13°
was excluded (since the undershoot tendency was observedin all subjects in the 12° trials, the lower threshold was set
as 9°). In all trials, the case in which the saccade latency
was below 80 ms or above 130 ms was excluded.
All images perceived in the saccade with a latency
between 80 ms and 130 ms were continuations of a straight
line, slant line, and straight line as shown in Fig. 6 left. Table
1 shows the saccade parameters of the subjects in thisexperiment. The values in the table are averages of 20 trials,
and the standard deviation is shown in parentheses. An
undershoot tendency is observed for the 12° amplitude, but
the saccade is stable in terms of both duration and latency.
The onset and offset of the saccade are defined asfollows. The measured data were passed through a 100-Hz

Fig. 6. Perceived image (left) and eye position (right).

80

Table 1. Amplitude, duration, and latency of measured
saccadesTable 2. Time gap of perceived images and measured
saccades, eye movement velocity, position, width of theperceived light locus, and ratio to amplitude

low-pass filter. Then, the first time at which the eye movement velocity exceeded 40°/s was defined as the onset ofthe saccade, and the last time when the eye movement
velocity was above 40°/s was defined as the offset of thesaccade.
3.5. Experimental results
Table 2 shows the time relation between the start/end
positions indicated by the subject and the eye movement.
The top item is the time difference, obtained by subtracting
the onset/offset time of the saccade (circle at right of Fig.
6) from the time when LED at the indicated start/end pointis on (cross at left of Fig. 6). The positive value at the startpoint implies that the perceived light spot locus starts tocurve after the onset of eye movement. The positive value
at the end point implies that the locus returns to the straightline after the offset of the eye movement.
As regards the perception at the starting point, theperceived light spot locus starts to curve after approximately 10 ms, as the average of four subjects, from the onsetof saccade, in both the 8° and 12° trials. At the end point,
the locus returns to the straight line in approximately 0 ms
in the 8° trial, and approximately 1 ms in the 12° trial after
the offset of saccade.
Figure 7 is a conceptual diagram based on the experimental data, the time course of the eye movement, the flash
timing of the light spot array, and the timing of the start/end
point of the perceived light spot locus. The vertical axis is
the eye position (deg) and the horizontal axis is the time(ms). The dotted line arrow indicates the period in which
the slant line is perceived, and the thick line arrow indicates

the time difference between the saccade onset and theperception start point.
In order to assure that the above time difference is notdue to pointing error of the laser pointer, the error between
the perceived position and the position indicated by thelaser pointer was measured. LEDs with the same intensity
as the light spot array were placed in an arrangement withthe same shape (left side of Fig. 6) and the same size (totalheight 12.8°, horizontal distance 5° between start and end
points and vertical distance 4°) as those of the actuallyperceived light spot locus for 8° saccade, and were flashedsuccessively from the top, each for 2 ms. The subjects
indicated the start and the end points without moving theireyes.
Table 3 shows the average error between the actually
flashed start/end points and the indicated positions. The
standard deviation is shown in parentheses. The first item

81

locus, that is, the width of the perceived light spot locus, tothe saccade amplitude. Except for the 12° trial of Y.A., thewidth is approximately 60% of the saccade width. For thesaccade amplitude, the average value for the start and theend points in the experiment is used.
3.6. Dependence on position of light spot
sequence
As regards the localization error for a flashed lightspot, it is known that the time locus differs depending on
the position of the light spot when a background is present[12]. Observing the spatial perception characteristics forthe equiluminant stimulus during saccade, as examined by
Ross and colleagues, the localization error reverses its signon both sides of the target position of the saccade [13].
Thus, it can happen that the spatial perception characteristics during saccade change depending on the positionof the stimulus presentation.
Consequently, the time relation between the perceived PA and the eye movement is examined in this study
by varying the stimulus position of the presented light spot
sequence. The experimental procedure, the device, and the
flash timing of LED are the same as in the previous experiment. The difference is that the position of the light spot
sequence for 128-ms flashing is set at one of –8°, –4°, 4°,
and 8°, not 0°. The time relation between the start/end pointof the perceived light spot locus and the eye movement is
examined.
The subjects were two of the persons (i.e., Y.I. andY.A.) who participated in the experiment with the light spot
array set at 0°. At any position, a light spot locus with asigmoid function shape, as shown at the left at Fig. 6, isperceived, with the same direction of movement. In thisexperiment, there is an intensity difference between thelight spot array and the background, and no stimulus ispresented that can serve as a cue after the saccade. Consequently, the reversal of the perception direction, as reported
by Ross and colleagues, was not produced [14]. The number of trials was 20 for each of the start and end points.
Table 4 shows the experimental results for the two
subjects. The values in the table are the average for each
item. The first item is the time difference between theonset/offset of the measured saccade and the perceived
start/end point. The time difference for the start point is 7.7
to 16.8 ms for Y.I., and 5.5 to 13.8 ms for Y.A. For the end
point it is –6.0 to 4.1 ms for Y.I., and –6.5 to –0.5 ms for
Y.A. Thus, both exhibited the same tendency as when thelight spot array was placed at 0°, namely, that the start pointis slightly after the onset of saccade, and the end point isalmost the same as the offset of saccade. Thus, we see thatthe time relation between the perceived PA and the eye

Fig. 7. Time course of eye position and light stimulus.

is the deviation represented by the view angle. The upperside is defined as positive. The second item is the timedifference in the experiment, converted from the error interms of the view angle. Thus, the sum of the first item inTable 2 and the second item in Table 3 is the time difference
between the actually perceived start/end point and the eye
movement. When this correction is applied, the averagetime difference for four subjects for 8° is that the starting
point is 11.3 ms after the onset of saccade, and the end pointis 1.6 ms after the offset of saccade.
The second item in Table 2 is the eye movement
velocity at the time when the start/end point is indicated.
The start point is perceived approximately 10 ms after the
onset of saccade. Consequently, the eye movement has
already reached a velocity of 150 to 250°/s. The end point,on the other hand, is perceived almost at the same time as
the offset of the saccade, and there are no data exceeding
100°/s.
The third item shows the indicated position of thestart/end point. The position is defined as positive in the
direction of the saccade, and is represented in terms of theview angle. The fourth item is the distance between the startpoint and the end point in the horizontal direction. It is theratio of the horizontal width of the perceived light spot

Table 3. Error of pointing82

Table 4. Time gap of a perceived image and a measured
saccade, position and width of the perceived light trace,and ratio to amplitude: data of Y.I. (above), Y.A. (below)

ment, on the other hand, the light spot array flashes fromapproximately 40 ms before the saccade to approximately
40 ms after the saccade. It has a period of 128 ms, and theperiod of light spot flashing is shorter than the period inwhich the spatial localization error is produced. This makes
it difficult to discuss the perception characteristics of therepeated flashing point, including all periods in which thespatial localization error is produced.
Consequently, the light spot sequence S was flashedsuccessively after the saccade target is on, 4 ms for eachspot, from the top for 256 ms, and we investigated whatlight spot locus the subject perceived. We found that thelight spot locus of the sigmoid function shape as in Fig. 6
was perceived in the same way as in the case of 128-ms
flashing. Since the on-time of each spot was increased, theslope of the slant line was closer to the horizontal line.
3.8. Difference depending kind of saccade
In this experiment, the express saccade with latency
stable in time was induced in order to establish stable
experimental conditions. It is known, however, that the
dynamic characteristics of the saccade, such as the amplitude, maximum velocity, and duration, change with the on
timing of the saccade target [16]. Consequently, the lightspot array was observed by varying the on timing of thetarget as 0, 50, 100, and 150 ms after vanishing of the target.
However, there was no change in the shape of the perceived
light spot locus.

movement is not affected by the position of the light spot
array in the environment of this experiment.
The second item is the positions of the perceived
start/end points. The direction of the saccade with respect
to the position of the light spot array is defined as positive,
and the value is represented in terms of the view angle. The
third item is the perceived horizontal width and the ratio tothe amplitude. In the data for Y.I., the perceived position isslightly affected. The position of the end point shifts in thesaccade direction as the light spot array moves in thesaccade direction, with the total width being somewhat
decreased. In the data for Y.A., the position and size of theperceived light spot locus are not affected by the positionof the light spot sequence.
It is generally understood that there is a large individual difference in the perception of the PA [15]. In thisexperiment, the individual difference is observed in thehorizontal position when the position of the light spot arrayis modified, but there is no significant difference between
individuals along the time axis.

4. Discussion
In this experiment, the light spot stimulus is presented
in the vertical direction in perisaccadic period, and thesubject is instructed to state the start point and the end pointof the perceived light spot locus. The result was that theperceived light spot locus started to curve at the onset of thesaccade in the opposite direction to the saccade, and returned to the vertical direction at the offset of the saccade.
Combined with the result of the preliminary experiment reported in Section 3.3, we see that the time at which
the light spot stimulus flashing in the vertical direction
started to curve was the start when PA is produced, and thetime when it returned to the vertical direction was the endof the PA spread. Thus, in contrast to the time course
expected in accordance with the cancellation theory, the PA
is perceived only during the saccade (this result agrees withthe results of the experiment by Oishi and Ebisawa, inwhich a single point was repeatedly flashed, beginning at atime prior to the saccade [2]).
As regards the direction of motion of the PA, a lightspot locus curving in the opposite direction to the saccade
was perceived in this experiment. This agrees with

3.7. When the on-time of light spot array isincreased
According to the study by Honda, the localization
error starts approximately 100 ms before the saccade andcontinues even approximately 100 ms after the saccade [7].
The localization error for flash stimulus occurs for a perisaccadic interval of approximately 250 ms. In this experi-

83Hershberger’s report [10]. But in the experiment on subjective observation by Oishi and Ebisawa, the PA moved in thesame direction as the saccade [2]. In fact, in Hershberger’s
experiment too, approximately 10% of the subjects perceived that the light spot moved in the same direction as thesaccade [10].
Assuming that the PA moves in the same direction as
the saccade when the light spot is moved in the verticaldirection as in this experiment, a light spot locus curving inthe same direction as the saccade should be perceived.
However, no such result was obtained in this experiment. It
is conceivable that the subjectively perceived direction of
motion and the actual eye movement do not necessarily
agree with the time relation.
If it is assumed that the right end of the PA in Oishi
and Ebisawa’s experiment is not the light spot which waspresented last, but the first light spot that started to spread,their results agree with the results of this experiment. The
following factors might produce the different views concerning the difference in the perceived direction of motion.
In Oishi and Ebisawa’s experiment, the focus point and thetarget point were always on. Repeated flashing of the lightspot was continued from 2 s prior to the saccade. There isalso an effect of the effort to control the attention [3].
The light spot locus perceived in this experiment had
the shape of the sigmoid function. The vertical straight line
was perceived before and after the saccade. The reason
seems to be as follows. In the perception of the repeatedly
flashing light spot, the image of the light spot which wason immediately before exists on the retina as a cue for
localization. Consequently, localization is performed on thebasis of the relative position information on the retina
before and after the saccade, where the eye is still [17].
Furthermore, the start of the observed light spot locus
was perceived as being displaced in the same direction as
the saccade, and the end was perceived as being displacedin the opposite direction to the saccade. The reason for themechanism that produces such a perception may be as
follows. During the saccade, in which the retinal information changes rapidly, the absolute spatial localization is
performed in accordance with the cancellation theory,
while referring to the eye position information. Then, theposition of the light spot before and after the saccade isreconstructed on the basis of the relative position relation,with the above cue as the reference. However, anothermechanism may be considered in which the velocity perception in the horizontal direction is reduced during saccade, and an image smaller than the horizontal movementon the retina is perceived [18], and the localization is
performed with those as a set of images [19].
In this experiment, the start of the perceived light spot
locus is approximately 10 ms later than the onset of thesaccade. The reason seems to be as follows. The spatial
localization mechanism cannot be switched quickly. Thus,

the information on the retina is located with an error in the
opposite direction to the saccade. But when the localization
is based on the cancellation theory, the error is in the same
direction as the saccade. These are canceled at the time ofswitching. In addition to such a factor related to the mechanism, the perception of the velocity in the vertical direction
may be affected in the saccade, as indicated in the reportthat the velocity perception after the saccade is enhanced in
the direction opposite to the saccade [20].

5. Conclusions
This paper has analyzed the time relation of theperceived locus for the repeatedly flashed light spot in theperisaccadic period to the eye movement, by successively
turning on the light spot array in the vertical direction. Thisis a point that has not been analyzed in the experiment of
Hershberger and colleagues.
This experiment showed that the time for which theinformation can be presented in SD is slightly shorter thanthe duration of the saccade. The direction in which thetwo-dimensional image spreads is opposite to the saccade,and the horizontal length for which the information can bepresented is approximately 60% of the saccade amplitude.

Acknowledgments. The authors are grateful for
useful advice given in this study by Mr. M. Imai, The
University of Tokyo, and Mr. A. Noritake, Kwansei Gakuin
University.

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AUTHORS (from left to right)

Junji Watanabe received his B.S. degree from the Department of Mathematical Engineering and Information Physics,
The University of Tokyo, in 2000, completed the M.E. program in 2002, and is now a doctoral candidate. His research concerns
displays based on eye movement and visual characteristics during eye movement. He is a member of the VR Society of Japan,
The Vision Society of Japan, The Institute of Image Information and Television Engineering, and Human Interface Society. He
has received a VR Society of Japan Paper Award (2001) and Encouragement Award (2002).
Taro Maeda (member) received his B.S. degree from the Department of Mathematical Engineering and Information
Physics, The University of Tokyo, in 1987 and joined the Mechanical Engineering Laboratory, MITI. He moved to The
University of Tokyo in 1992, and has been a lecturer in the Graduate School of Interdisciplinary Information Studies since 2000.
His research interests are modeling of human perception characteristics and neural network, as well as tele-existence. He hasreceived a Society of Instrument and Control Engineers Paper Award and Encouragement Award, and Technology Award fromthe Robotics Society of Japan.

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AUTHORS (continued)

Susumu Tachi (member) received his B.S. degree from the Department of Mathematical Engineering and Information
Physics, The University of Tokyo, in 1968 and completed the doctoral program in 1973, receiving a D.Eng. degree. Afterbecoming a professor at the Research Center for Advanced Science and Technology (1992) and the Department of MathematicalEngineering and Information Physics (1994), he has been a professor of information physics and computing in the Graduate
School of Information Science and Technology since 2001. His research interests are tele-existence and virtual reality. He hasreceived an IEEE/EMBS Award, MITI Minister’s Award, and Special Achievement Award from the International Measurement
Confederation. He served as Chairman of the IMEKO Robotics Conference and is a past president of the VR Society of Japan.
He is an SICE fellow.

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