Positive Effect of Slight Delay for Operational
Performance
1st Ryota Akimoto
2 Masatoshi MiyajindNagoya Inst. of Tech., Japan

3rd Kenji Funahashi

4th Koji Tanida

5th Shinji Mizuno

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

Kindai Univ., Japan
tanida@mech.kindai.ac.jp

Aichi Inst. of Tech., Japans mizuno@aitech.ac.jp

Abstract—Experienced tool manipulators often describe thatthey can move a tool in the way they intend like a part ofthe body. Based on the ﬁndings from experiments about delay,
we hypothesized that appropriate delay in a control system
would help us to understand the characteristics of tools andwould improve operational performance. It was suggested thatappropriate delay improved operational performance for a little
difﬁcult operation.
Index Terms—sense of self ownership, slight delay, operational
performance

I. I NTRODUCTION
In the ﬁeld of cognitive science, research on self awareness has been performed, and Gallagher has proposed thepsychological concepts of the sense of self agency and self
ownership [1]. The sense of self agency is the sense that they
are the cause or author of the movement, and the sense of self
ownership is the sense that they are the subject of the movement. The research [2] has shown that the sense of self agency
is stronger when the delay and noise between the operationand the object motion is smaller. Waltemate et al. showed thatmotor performance, the sense of self agency and the sense of
self ownership decline with a certain amount of latency for a
subject’s body action in VR environment [3]. Tochioka et al.
showed that the sense of self ownership was just decreased
monotonically in the situation where the latency of a subject’s
hand motion was long, that was realized and experimented in
AR environment [4]. We had expected that same results wereobtained for tool operation, and experimented them in VR
environment. Although the sense of self agency and the senseof self ownership had a similar tendency for the researches
described above, it was suggested that slight delay improved
tool operation performance unexpectedly. 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 (end of section 2.2 in [5]).
Farrer also had an experiment about the change of the senseof self agency when adding delay for displaying the response
on a screen after pressing a button [6]. In this experiment,
it was found that increasing the delay resulted in subjects
responses varying from full control, to partial control and tono-control. A person who is skilled in the manipulation of atool may feel the tool as if it were their own hand or foot. The
phrase “I can move a tool like a part of the body in the way
I intend” is sometimes used not only for i.e. a tennis racket
that appearance and how to use are similar to a part of a bodyand its action (compare the following car example), but also
for i.e. a car that is not similar [7], [8].
In this study, we focus on this sense that a person feels atool as an integral part of themselves, and they feel it as
if it were a part of the body. In order for a person who is
not skilled in tool manipulation to feel this sense and to use
tools better, it is necessary to recognize tools appropriately
and not to be pushed around. Based on the ﬁndings of Farrer’s
experiment, it can be expected that a small delay is effective
for proper recognition for the other stuff. In the experiment,
we examined the effect of the delay between input operationand output response for the tool manipulation. The operation
was a moving object task as continuous movement by reachextender, it meant grabber, which was more difﬁcult thansimple button pressing task. Kasahara i.e. showed that spatialtemporal deformation of a virtual body actually changed thesense of body as well as physical movement [9]. We also
examined the effect of the difﬁculty to operate for the sense.
The difﬁculty was expressed as a length of a reach extender.
It was suggested that appropriate delay improved operational
performance for a little difﬁcult operation. However, in thecase of very easy and difﬁcult tasks, the positive effect ofthe delay was not noticeable. This was expected to provide
insights for development of interface also for VR systemthat enables even person who is not skilled in manipulation
to effectively acquire the sense of self ownership for tool
operation.
II. E XPERIMENTAL SYSTEM
We consider an experiment that a subject moves an object
by a tool in a VR environment. A reach extender is used
as a tool, and a subject moves a ball as an object from one
table to another (Fig. 1 (a)). Two tables are also prepared in
a VR space. The movement of the reach extender is linked
to the stylus of force feed back and 6DOF pointing device
PHANTOM Omni (Fig. 1 (b)). The virtual reach extendermovement is delayed for PHANTOM to delay it for the motionof the subject’s hand. A cardboard is placed to prevent the
subject from seeing at PHANTOM.

The motion of a tool and an object can be divided into two
types: one is steady state, such as constant speed linear motion,
constant acceleration rotational motion and stopped state, andanother is transient state. In this experiment, we focus on the
delay in the transient state, because the delay in the steadystate may not be easily recognized. Therefore, we choose thetask that is started clearly and proceeded in short period. Inorder to measure operation time, the object is ﬁxed before start.
We draw a “lid” on the object to represent visually that it is
ﬁxed (Fig. 1 (c)). The PHANTOM stylus is also prevented
to limit the reach extender. A three second countdown isdisplayed to announce the start of the move operation. Afterthe countdown, a subject can move the object. The delay canbe changed also to zero but it actually includes PHANTOM
communication and drawing time. It is supposed that shaft
length of the reach extender is 25mm, and the total length
between tip of jaws and trigger of handle is 60mm because of
movable range of PHANTOM, and the VR scene is displayedon a 22 in. screen at about 3.4 times the size (Fig. 2), itmeans the total length seems about 200mm. If the positionof the tables is always the same, the subject may become
accustomed to the operation. So the position of the tables
is changed in parallel and symmetrical randomly, but thisdistance is always constant, because the fairness of the task
cannot be maintained if the distance between them changes.
Horizontal distance between the center of tables is 110mm,
vertical distance between the top of tables is 50mm, andabsolute distance is 120mm, that seems about 400mm.
III. E XPERIMENT 1

Fig. 1. Appearance of experiment.

Fig. 2. Top view of positional relationship.

A. Exploratory experiment
We had expected that same results were obtained for tool
operation, and experimented them in VR environment ﬁrst.
The subjects were 20 undergraduate and graduate students
in their 20s. Consent to participate in the experiment was
obtained from all subjects. Before the experiment, we provided
the subjects with a few minutes of practice to familiarize
themselves with the experimental system and PHANTOM, andto experience the following standard actions 1 to 4 in orderfor them to understand the task to move an object by using
the reach extender.
Action 1: Manipulate an actual object (sponge ball)directly by hand (Fig. 3 (a)).
Action 2: Manipulate an actual object (sponge) directly
by an actual reach extender (Fig. 3 (b)).
Action 3: Manipulate a virtual object with no delay by avirtual reach extender.
Action 4: Manipulate a virtual object with the maximum
delay in this experiment.
This action 1 meant direct operation by their own hand without
any tool. Action 2 was the operation with a reach extender
as a tool in real world. It assumed that the action 3 wasequivalent to action 2. And the subjects had an experience
about delay with action 4. We also explained that thesebehaviors were used as a measure of the responses to theFig. 3. Appearance of standard action.

post experimental questionnaire. In our experiments, the delay
was 0[ms] (although about 5[ms] was included as PHANTOM
communication and drawing time, but we treated this as
no delay) to 450[ms], with 10 steps of 50[ms]. Subjects
performed 10 movement tasks (5 round trips) in a trial. In
experiment 1, we assigned ﬁve delay patterns for each subject
as ﬁve trials (50 tasks) in random order from 10 patterns. After
experiencing the standard actions, the experiment was carriedout as follows. The evaluation was based on the subject’s
responses to a questionnaire about the sense of operation andthe time spent to move from one table to another.
Step 1: The delay and the table positions were set initially.
Step 2: Operated the PHANTOM to grab an object on
the table by the virtual reach extender.
Step 3: Performed the task 10 times (5 round trips).

3-1: Waited for 3 seconds in the countdown.
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.
Question 1: Were you able to move the reach extender with your own intentions (the sense of self
agency)?
Question 2: Did you feel the reach extender as if itwere your own hand (the sense of self ownership)?
Questions 1 and 2 were rated on a scale of 0 to 9. We asked
the subjects to evaluate each trial as follows: the action 1 bytheir own hands was 10 (greater than 9), the action 2 and 3 by
the real and virtual reach extenders were 5, and the action 4
with the maximum delay was 0.
B. Result of experiment 1
The results were broadly similar to those of previous
studies in terms of the sense of self agency and the senseof self ownership. The evaluation value about sensation during
operation became smaller as the delay decreased overall in theexperiment 1 (Fig. 4). Although the value of the sense of self
agency in the range of 0-150[ms] became smaller as the delay
increased, the value of the sense of self ownership was almost
constant in the same range. A Wilcoxon rank sum test was
conducted on the sensory evaluation at 0 and 150[ms]. There
was a signiﬁcant difference between 0 and 150[ms] at the 5%
level for the sensory evaluation of the sense of self agency,
whereas there was no signiﬁcant difference for the sensory
evaluation of the sense of self ownership. This suggested
the existence of the sense of self ownership between 0 and150[ms] delay. However, the transitions in sensory evaluationsof both were similar overall. A two way test of variance wasconducted between the both results and the amount of thedelay. There was no signiﬁcant difference between two sensory
evaluations, and no interaction. The value of the Fig. 4 (b) at
0[ms] was above 5, it meant that some subjects felt that thesensation was more similar to the sensation of manipulating
an object directly by hand than without the delay.
The average operation time increased as the delay increased
overall in the experiment 1 (Fig. 5). However, the average
operation time at 100[ms] was shorter than the time at 0[ms].
It was analyzed whether there was a signiﬁcant difference
between the average operation time with a delay of 0 and100[ms]. There was signiﬁcant difference at the 5% level.
This suggested that appropriate delay in the control system
improved the operational performance. Furthermore, there wasno signiﬁcant difference between 50 and 100[ms], and there
was signiﬁcant difference between 100 and 150[ms] at the
1% level. These suggested surprisingly that the appropriatedelay improved the operational performance was about 50 to
100[ms]. Now it was examined whether experience and fatigue
affect on the operation time. A two way test of variance wasconducted for the ﬁrst, sixth, and tenth total permutations of
the task and the amount of the delay. There were no signiﬁcantdifferences in operation time by task order in each trial, andthere was not interaction between the task order and delay.
This suggested that experience and fatigue did not affect on
the operation time.
IV. E XPERIMENT 2
A. Revalidation experiment
Appropriate delay in the control system might improve theoperational performance in experiment 1. We tried to examine
it again with other subjects, and the same experimental systemand the same procedure. The subjects were 30 undergraduate
and graduate students in their 20s. Consent to participate in theexperiment was obtained from all subjects. For each trial, theyanswered the following questionnaire about their sensations
during operation instead of the Step 4 in section III-A:
Step 4’: For each trial, answered the following questionnaire about their sensations during operation.
Question: Did you feel as if the other were intervening in the manipulation of the reach extender (thesense of the presence of the other)?
Question was rated as follows: cooperative interference waspositive point (maximum 5), obstructive interference wasnegative point (minimum -5), and no interference felt was zero
point. Note that we told them before this experiment that it
might work with not only obstructive delay but also cooperative support, even though cooperative operational support
was not provided actually. The minimum effective delay in theexperiment system was 16[ms] due to the modiﬁcation of thedrawing process, and 8 trials were allotted per a subject.
B. Result of experiment 2
Unfortunately, the average operation time in the experiment 2 (Fig. 6) was not improved as clearly as in experiment 1.
By the way, the subjects really felt the other as cooperator
between 0 and 200[ms] without any actual support, and felt
the other as obstacle for delay longer than 250[ms] (Fig. 7),
although there was no signiﬁcant difference unfortunately. It
maybe expected that people can easily feel the sensation thatthey can move a tool like a part of the body in the way they
intend by adding a slight delay.
V. E XPERIMENT 3
A. Difﬁculty experiment
Although appropriate delay might improve the operational
performance in experiment 1, favorable result was not obtainedin experiment 2 for performance. On the other hand many
subjects felt the other as cooperator without any actual supportin experiment 2. We examined them repeatedly with othersubjects. And also to examine the effect of the difﬁculty of atool, the system used in experiments 1 and 2 was modiﬁed forthis experiment. The shaft length of the virtual reach extendercan be changed to three different length: 0.5, 1.0 and 1.5
times (Fig. 8). The subjects were 9 undergraduate and graduate
students in their 20s. Consent to participate in the experimentFig. 8. Three lengths of reach extender.

Fig. 4. Transition and variability between amount of
delay and evaluation of (a) the sense of self agency,(b) the sense of self ownership (experiment 1).

Fig. 5. Transition between amount of delay andaverage operation time in the experiment 1.

Fig. 6. Transition between amount of delay andaverage operation time in the experiment 2.

Fig. 7. Transition and variability between amountof delay and evaluation of the sense of the otherpresence in the experiment 2.

Fig. 9. Transition between amount of delay
and average operation time for (a) 0.5 times
length, (b) 1.0 time length, (c) 1.5 times
length, (d) all pattern lengths (experiment 3).

was obtained from all subjects. It was focused on how positive
peak of the sense of the other presence as cooperator (Fig. 7)
was changed depending on the difﬁculty, so the delay was set
as 25 to 175[ms], with 7 steps of 25[ms]. We assigned just 14
patterns for each subject as 14 trials in random order from 3
lengths and 7 delay patterns. Note that no subject was assigned
the same combination of length and delay pattern again. This

Fig. 10. Transition and variability between
amount of delay and evaluation of the senseof the other presence for (a) 0.5 times length,(b) 1.0 time length, (c) 1.5 times length, (d)all pattern lengths (experiment 3).

experiment procedure was almost same as experiment 2. Whensubjects experienced the standard actions, only original length
reach extender was used.
B. Result of experiment 3
The average operation time was constant overall when thelength was 0.5 or 1.5 times as the delay increased in theexperiment 3 (Fig. 9). However, the average operation timein the range of 50-75[ms] was shorter than the time at 25[ms]when the length was 1.0 time (Fig. 9 (b)). It was analyzed
whether there was a signiﬁcant difference between the average
operation time with a delay of 25 and 50[ms], 25 and 75[ms].
There was signiﬁcant difference at the 1% level. The average
operation time at 150[ms] was shorter than the time at 75[ms]of the 0.5 times length (Fig. 9 (a)), and the transition wasalmost constant of the 1.5 times length (Fig. 9 (c)). The appropriate delay really improved the operational performance forthe original size, however the appropriate delay for different
difﬁculty might change, and the delay did not work well for
more difﬁcult tool. By the way, the operation time of the 1.0
time length was longer than the time when the length was
0.5 or 1.5 times at 25[ms]. Although the task is more difﬁcult(longer length reach extender), the operation time is longer ingeneral, this result were not. It might suggest that the subjects
prepared for more difﬁcult task before starting if the reachextender was too long.
The subjects felt the other as cooperator between 50 and about
125[ms], and felt the other as obstacle for delay longer thanabout 175[ms] for all lengths (Fig. 10). This suggested that it
almost did not depend on the length whether they felt the otheras cooperator or obstacle. However, It depended on the length
whether they felt the other presence strongly. Comparing sumsof positive average values and negative ones, the value of the
1.0 time length was grater than the value of the 0.5 and 1.5
times length. This was thought that subjects felt the otherpresence weakly when the task was easy (shorter length reachextender), whereas the subjects were too concerned about task
operation to feel the other presence when the task was difﬁcult.
It is considered the relation between the operation time and theother presence here. (1) The values of the other presence forthe 1.0 time length were relatively grater than the values for
the 0.5 and 1.5 lengths in the range of 50-75[ms] (Fig. 10 (d)).
There was signiﬁcant difference between the average operation
times for the length of 1.0 time and both of 0.5 and 1.5
times in the same range of 50-75[ms] (Fig. 9 (d)). (2) The
subjects felt the other as cooperator when the length was
0.5 times, whereas they felt the other as obstacle when thelength was 1.0 and 1.5 times at 150[ms] (Fig. 10 (d)). It
meant that they felt the other more cooperative relatively
at the time. There was signiﬁcant difference between the
average operation times for the length of 0.5 times and bothof 1.0 and 1.5 times at 150[ms] (Fig. 9 (d)). (3) Although
this was a same result as experiment 1, when the subjects
felt the other as most cooperative in the range of 50-75[ms]for the 1.0 time length (Fig. 10 (b)), the operation times
decreased certainly for other delay trials (Fig. 9 (b)). These
considerations suggested that the operation time decreased
when they felt the other as cooperator, and the appropriatenessand effectiveness depended on the difﬁculty of manipulation.
VI. C ONCLUSION
We examined the effect of the delay between input operation and output response, and the effect of the difﬁculty tooperate. Experiments were conducted to test the hypothesisthat appropriate delay in the control system would help a user
to understand the characteristics of a tool (the other stuff),
and thus the delay might lead to the sense of self ownership. It
was suggested that appropriate delay gave subjects cooperative
sensation of the other, and this sensation might give subjects
the sense of self ownership, and improved operational performance for a little difﬁcult operation. However, the positiveeffect of the delay was not noticeable in the case of very easy
and difﬁcult tasks. It maybe expected that people can easily
feel the sensation that they can move a tool like a part of the
body in the way they intend by adding a slight delay.
This ﬁnding is expected to provide insights to develop interfaces also for VR system that enables even person who is
not skilled in manipulation to effectively acquire the sense of
self ownership. In the future, the number of subjects should be
increased to get more accurate data. Consideration of statistics,
such as p-value, degree of freedom, and testing methods,
should be deepened. In order to be conﬁrmed that subjects
perceived it as an obstacle for delay above 175[ms], it should
be analyzed 200[ms] and above. By the way, some subjects
felt pseudo support without any actual support, so we would
like to consider how the sense of the other presence changes
when actual support is also provided.
ACKNOWLEDGMENT
This work was supported in part by JSPS KAKENHI Grant
Number JP20K11918.
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