Positive Effect of Slight Delay and Task Conditions
for Operational Performance
Yakumo Miwa

Kenji Funahashi

Nagoya Inst. of Tech., JAPANy.miwa.915@stn.nitech.ac.jp

Nagoya Inst. of Tech., JAPANkenji@nitech.ac.jp

Abstract—We have hypothesized that providing the control
system with an appropriate delay would improve its operational
performance. Previous experiments in our laboratory have suggested that slight delay in the operation of a tool improves
operational performance. However, another experiment withslight changes in appearance and task details did not show
positive effects. In this study, we investigated the requirements forslight delay to improve performance. By adjusting the task while
keeping the appearance unchanged, we again obtained results
suggesting an improvement in tool operational performance. The
effect of the difficulty of the operation task was also inferred.
Index Terms—User Interface, Tool Operation, Positive Effectof Delay

Koji Tanida

Shinji Mizuno

Kinki University, JAPAN Aichi Inst. of Tech., JAPAN
tanida@mech.kindai.ac.jp
s mizuno@aitech.ac.jp

Fig. 1. Screen of experiment 1

I. I NTRODUCTION
We have investigated the effects of latency to tool operation [1]. It is generally believed that latency only negatively
affects the feeling of operation [2] [3]. By the way, Mazda
which is Japanese automobile manufacturer has reported thatslight delay is important element apparently—When you start
to move the accelerator pedal, the time until the tension of
the neck muscle starts is constant at 0.2 to 0.3 seconds. It
is the first necessary condition that acceleration is generated
in accordance with the “timing of the stance” to realize areasonable and natural reaction (last part of section 2.2 inreference [4]). Based on the findings from experiments ondelay [5], we have hypothesized that providing the control
system with appropriate delay would improve its operational
performance. We conducted an experiment on relatively simple
tool operation to investigate the effect of delay. The experiment was conducted in a VR environment in order to easily
implement delay in tasks that were somewhat more complex
than simple button pressing operations [5]. A reach extender
was displayed on the screen. The subjects operated the reachextender with a 3D position input device. The reach extender
moved a ball from one table to the other in the screen (Figure 1
and 2). Delay was intentionally added between the operationof the input device and the reaction of the reach extender on
the screen. As a result, the performance was improved (i.e. thetime to move the ball decreased) at small delay of about 50
to 100 ms, and degraded at larger delay [6] (Figure 3, called
experiment 1 in this paper, described again in English [7]). We
performed a same experiment again to reconfirm this result [7](called experiment 2 in this paper). In addition, the subjects
were informed in advance that it might assist or disturb themwith a force display device even though any force was not

Fig. 2. Screen of experiment 2

provided actually. Sensory evaluation was conducted after theexperiment. The result showed that although the subjects feltthat they were assisted at delays of 50 to 150 ms (Figure 4,
positive value means assistance), no clear improvement in
performance was observed (Figure 3). At larger delay, theperformance clearly decreased, and the subjects felt that they
were disturbed. The experimental system for experiment 2 wasa same as that for experiment 1, but was revised to use 3DCG
in the hope that a more pronounced trend would emerge.
Initially, it was assumed that the slight differences would haveno essential effect on the results and that similar trends would
be obtained. However, the results were as described above. In
this study, we first sort out the differences between the two
experiments. And then, additional experiments are conducted
to evaluate what factors lead to a positive effect of delay.
It is expected that delay in tool operation would alter thesense of agency and the sense of self-ownership [8], and slightdelay may be useful for interface design. However, the main
objective of this study is not to focus on the mechanism bywhich delay improves tool operation performance, but rather to
identify the conditions under which performance improvement
occurs.

Fig. 5. Appearance of experiment 2

Fig. 3. Result of operating time of experiment 1 & 2

Fig. 6. Actual operation by (Left) a hand, (Right) a reach extender

the following standard actions 1 to 4 in order to understandthe positioning of the task.
Fig. 4. Sense of the other presence in experiment 2

II. E XPERIMENT 1 & 2
A. Experiment System and Procedure
In the experiment, a PHANTOM (Geomagic PhantomOmni) was used as an input device (successor product [9]),and a 22-inch LCD display was used as the output device (Figure 5). The reach extender displayed on the screen was linked
to the PHANTOM stylus. The subject operated the reachextender on the screen and moved the ball object on the screen
from a table to another table through the PHANTOM. Delayis added between the PHANTOM and the reach extender toimplement the delay from the subject’s hand to the extenderand the movement of the object. It was necessary to measure
the movement time of the object to obtain the operation scores.
It was also needed to clearly distinguish between steady state
and transient state. A “lid” was drawn on the object to visuallyindicate that it was fixed. The reach extender on the screen
was also restricted to move, and the PHANTOM was fixed. A
3-second countdown was displayed in numerals to announce
the start of the movement operation. After the countdown, thesubject could move the reach extender. If the positional relationship between the tables was always the same, the subject
might become accustomed to the operation, so the position of
the tables could be changed. However, these distances should
not differ significantly, because changing the distance between
each other would not maintain fairness among tasks and wouldinterfere with the evaluation of movement time.
Prior to the experiment, subjects were asked to experience

Action 1: Operate an actual object (sponge ball) directly bya hand.
Action 2: Operate an actual object (sponge) directly by anactual reach extender.
Action 3: Operate a virtual object with no delay by avirtual reach extender.
Action 4: Operate a virtual object with the maximum delayin this experiment.
This action 1 meant direct operation by their own hand without
any tool (Figure 6 (Left)). Action 2 was the operation with areach extender as a tool in real world (Figure 6 (Right)). It
assumed that the action 3 was equivalent to action 2. And
the subjects had an experience about delay with action 4. The
delay in the experiment was 0 ms (although about 5 ms inexperiment 1 and 16 ms in experiment 2 were included as a
PHANTOM communication and drawing time, each delay wastreated as no delay) to 450 ms, with 10 steps of 50 ms. The
past positions of the PHANTOM stylus were stored, and thescene was drawn with the position according to the delay. The
refresh rate was not affected by the delay. Subjects performed
10 movement tasks (5 round trips) in a trial as follows.
Step 1: The delay and the table positions were set initially.
Step 2: Operated the PHANTOM to grab an object on thetable by the virtual reach extender.
Step 3: Performed the task 10 times (5 round trips).
Step 3-1 : Waited for 3 seconds in the countdown.
Step 3-2 : Moved the object to another table quickly andsmoothly as possible.
Step 4: For each trial, answered the following questionnaireabout their sensations during operation only in experiment 2. (Note that the subjects were informed inadvance that it might assist or disturb them with aforce display device even though any force was notprovided actually.)
Question: Were you able to move the reach extender withyour own intentions (the sense of self agency)?
In experiment 1, 20 subjects were assigned 5 trials and 5
delays per subject in random order. In experiment 2, 30
subjects were assigned 8 trials and 8 delays per subject inrandom order.
B. Differences of Experiment 1 & 2In this section, we discuss the differences between theexperimental systems. First, the differences are listed.
(1) Operating movement(1)-1 With/without depth movement restrictions(1)-2 Movement ratio of reach extender on screen to
input device(2) Table(2)-1 Size of table(2)-2 Positioning of table(3) Visual size(3)-1 Size of monitor(3)-2 Size of window(4) Depth perception(4)-1 Angle of depression(4)-2 Projected shape of floor(5) Appearance(5)-1 Color tone(5)-2 Shading
Each item is described in detail as follows.
(1)-1: In experimental system 1, depth movement wascompletely restricted to simplify the task (Figure 7, 8 (Top)).
In experimental system 2, depth movement was allowed withina certain range in the hope three-dimensional movement
would increase the sense of realism and make the delay effectmore positive (Figure 7, 8 (Bottom)). It was expected thatthe difficulty of the operation would not change because thedepth movement direction was limited to the diameter of thetable. However, the range of the left and right coordinates of
the target table differed according to the depth coordinates.
(1)-2: The relationship between the actual hand movement
and the movement of the reach extender is consideredhere. It means the ratio of the hand coordinates to thescreen coordinates. The experiment system 1 was projected
orthographically, and the system 2 was projected perspectively,
but they were not displayed stereoscopically. Because it isunknown how subjects perceive depth, the actual distancefrom the monitor surface was used as the distance inscreen coordinates. The table is drawn smaller at theedge of the monitor than at the center in the perspective
projection. Therefore, they are measured around the tables
in experiment 2. Table 1 shows the relationship between

the distances based on the hand coordinate distance. Whenthe hand moves a certain distance, the reach extender on
the screen moves about twice as far in experiment 2 as inexperiment 1.
(2): The position and the size of the table for each experimentwere set experimentally. There were three different layouts ofthe tables for each experiment. Each closest layout in eachexperiment was called as type 1, 2 and 3. Table 2 shows
the relationship of the size and position of each table. The
distance values are: the diameter of the table / the verticaldistance between the centers of the tables / the horizontal
distance between the centers of the tables / and the direct
distance between the centers of the tables. One layout wassymmetrical with another in both experiments, and one layout
was overall higher than another in the experiment 2. Notethat the starting table size was different in experiment 1:
43.1 mm in the hand coordinate system, and 34 mm in thescreen coordinate system. The averages of the horizontal
hand coordinate distance were approximately a same, butothers were different.
(3): Both monitors were the same: BenQ G2200W 22 incheswith 1680 × 1050 pixels. The window size was 800 × 800 for
experiment 1, as shown in Figure 1. Experiment 2 was 1680
× 1050 (full screen), expecting that a wider viewing angle
would have more positive effect by increasing the sense ofpresence.
(4), (5): The depression angle of the gaze is difficult
to indicate simply because the pseudo-three-dimensional
effect was expressed based on orthographic projection inexperiment 1. The angle was 15.8 degrees looking down inexperiment 2. Each floor is shown in Figure 1 and 2. The
color tone, shading, etc. are also as shown in Figure 1 and 2.
In the following sections, we first focus on (1)-1 mentioned
above and conduct experiment 3 based on experiment 2, i.e.
keeping (2)-(5) the same as in experiment 2 but completely
restricting movement in the depth direction as in experiment 1.
Next, focusing on (1)-2, we conduct experiment 4 basedon experiment 2, where only the ratio of the actual hand
movement to the reach extender movement in the screen is thesame as in experiment 1. Finally, experiment 5 is conductedbased on experiment 2, in which both the restriction of depth
movement and the ratio of the movements are adjusted tothose of experiment 1.
III. E XPERIMENT 3
Based on the experimental system 2, we conducted
experiment 3 in which the depth movement was restrictedin the same way as in experiment 1. The object could only
be moved in a vertical plane. Consent to participate in theexperiment was obtained from all participants. Each of the
24 subjects was assigned 10 trials with 10 delays in random
order. The preparation and procedure of the experiment were
the same as in experiment 1 and 2 described in Section II.A.
The average time of the task operation was longer for larger
delay (Figure 9). However, the operating time was shorter

TABLE I
R ELATIONSHIP OF HAND AND SCREEN COORDINATE DISTANCE
Expt.1, 4 & 5
Expt.2 & 3

Hand coord. dist. [mm]1
1

Screen coord. dist. [mm]
0.78
1.48

TABLE IIS IZE AND POSITION OF TABLE
Fig. 7. Side view of experimentFig. 8. Ground view of (Top) experiment 1, (Bottom) experiment 2

with 50 ms delay than with 0 ms delay. There was no
significant difference between the time with a delay of 0 ms
and that with the experiment 1, and it was expected that thedepth-movement restriction had effect on the improvement ofoperational performance due to the delay.

(diameter/vertical distance/horizontal distance/linear distance)
Expt. - Type
Hand coord. dist. [mm] Screen coord. dist. [mm]1-171.8/144/144/203
56/113/113/160
1-2
71.8/162/162/229
56/127/127/179
1-3
71.8/162/162/229
56/127/127/179
Avg. of expt.1
71.8/156/156/220
56/122/122/173
2-1
46/67/147/161
72/88/221/238
2-2
46/67/147/161
72/91/225/242
2-3
46/67/147/161
72/88/221/238
Avg. of expt.2 & 3
46/67/147/161
72/89/222/239
Avg. of expt.4 & 5
46/67/147/161
36/46/114/124

perceived as easier in terms of impression. The subjects were
10 students. All participants consented to participate in theexperiment. Each subject was assigned 10 trials with 10 delays
in random order. Preparation and procedure for the experimentwere the same as in experiments 1, 2 and 3. The average timeof the task operation was longer for larger delay (Figure 10).
The average operating time was slightly shorter with 50 ms
than with 0 ms delay like the result of experiment 3. There
was no significant difference between the time with a delayof 0 ms and that with a delay of 50 ms as a result of MannWhitney U test. The trend of the operating time was slightly
similar to that of experiment 1, and it was expected that the
movement ratio of reach extender on screen to input device
had effect on the improvement of operational performance dueto the delay.
V. E XPERIMENT 5

IV. E XPERIMENT 4
Based on the experimental system 2, experiment 4 was
conducted in which the ratio of the movement of the reachextender on the screen to the movement of the input device
was the same as the experiment 1 (Table 1). The size andposition of the table were the same as in experiment 2 and 3,
and the hand movement during task operation was also thesame. The movement of the reach extender and the ball object
in the screen was about a half. In experiment 4, the size andposition of the table (Table 2, experiment 2) did not change
in the hand and table coordinates. The average distances inthe screen coordinates were 36/46/114/124mm (Table 2). The
actual hand movements were smaller in experiments 2 and 3
than in experiment 1, but they were larger on the screen. The
hand movement remained small, and the movement on thescreen was also small in experiment 4. In experiment 4, theactual movement and the size of the table were not changed,
but only the appearance on the screen was changed. So theease of the task should not have changed, but it might beExperiment 5 was also based on the experimental system 2,
its depth movement was restricted as in experiment 1 and 3,
and its ratio of the reach extender to the input device was
the same as the experiment 1 and 4. The subjects were
10 students. All participants consented to participate in theexperiment. Each subject was assigned 10 trials and 10
delays in random order. Preparation and procedure were thesame. The average time of the task operation was longer forlarger delay (Figure 11), but the operation time was shorter
with 50 ms delay than with 0 ms delay. And there was 5%
significant difference between the time with delay of 0 ms
and that with delay of 50 ms as a result of Mann-Whitney
U test, the same as the improvement in experiment 1. The
result clearly suggested a positive effect of slight delay as
in experiment 1. Both the limitation of movement and theratio of movement might be necessary to indicate the positiveeffect of the delay. However, it is not clear whether further
decreasing the movement ratio would lead to better results.

the size or decrease the distance in the hand coordinate
with/without changing it in the screen coordinate.
ACKNOWLEDGMENT
This work was supported in part by JSPS KAKENHI Grant
Number JP20K11918 and JP23K11182.
R EFERENCES

Fig. 9. Result of operating time of experiment 3

Fig. 10. Result of operating time of experiment 4

Fig. 11. Result of operating time of experiment 5

VI. C ONCLUSION
We sorted out the differences between two experimentsthat gave different results in confirming the positive effect ofslight delay, and investigated which differences lead to positiveeffect on delay. The experiments focused on the restrictionof depth movement, and the ratio of the reach extendermovement on the screen to the actual hand movement. The
experiments only with restricted depth movement and onlywith readjusted ratio of the extender to hand showed trend
toward improved performance, but there were no significant
differences. The experiment with the depth restriction andthe readjusted ratio showed improvement in performance with
5% significant difference. These may be simplifications of
the task itself, and simplifications in mental images. In otherwords, the task difficulty may have strong influence on theperformance improvement due to slight delay. These findings
will contribute to user interface design. In the future, we would
like to investigate the simplified task about the tables; increase[1] T. Kataoka, K. Funahashi, K. Tanida and K. Yashiro. A Study of Sense of
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