"©2008 IEEE. Personal use of this material is permitted. However, permission toreprint/republish this material for advertising or promotional purposes or for
creating new collective works for resale or redistribution to servers or lists, or toreuse any copyrighted component of this work in other works must be obtained
from the IEEE."

2008 IEEE International Conference on
Robotics and Automation
Pasadena, CA, USA, May 19-23, 2008

Identification of Cutaneous Detection Thresholds against
Time-delay Stimuli for Tactile Displays
Shogo OKAMOTO, Masashi KONYO, Satoshi SAGA and Satoshi TADOKORO
Abstract— Tactile display is a technology that gives an artificial sense of touch to operators of information terminals
or master-slave systems. The generation of tactile stimuli in
response to the hand movements of the operators is associated with active touch and is considered to be one of theeffective display methods, however which inevitably causes
delayed tactile feedbacks from tactile displays. The knowledgeof the detection threshold of system latency between the hand
movements and the stimuli is helpful in designing the tactile
displays. In this study, the identification of the thresholds
through psychophysical experiments of 13 participants revealed
two types of thresholds. One was the time-delay at which theparticipants observed the existence of latency. The other was theminimal time-delay that could affect the subjective feelings ofthe operators while they were not conscious of the latency. The
means of the thresholds were 41 ms and 59 ms, respectively.
The participants reported that the time-delay stimuli caused
various changes in their subjective feelings. The empiricalresults suggest that the two types of thresholds depend on
different sensory processes. This paper also proposes a design
policy for tactile display systems in terms of system latency.

I. INTRODUCTION
For tactile displays, a display method that produces appropriate tactile stimuli in response to the hand motionsof operators is effective to induce the natural sense of
touch. The method is compatible with active touch, because
the operators move their hands and experience cutaneous
sensations as well as when they touch real objects.
However, in this method, there is an inevitable timedelay between the hand movements and the stimuli presented
by the tactile displays. When the delay is significant, theoperators do not consider that the stimuli are causal effects of
their motions, or they feel that virtual objects move unnaturally by themselves. The identification of cutaneous detection
thresholds against the system latency is helpful in designing
the tactile display systems in which hand movements are
inputs and tactile stimuli are outputs.
The aim of this study is to investigate two types of detection thresholds. It is possible that the following two types of
the thresholds exist. One is a minimal time-delay at which theoperators can notice its presence. When the system latency
exceeds this threshold, the operators notice that the tactile
feedback is delayed. The other threshold is a minimal timedelay that affects the tactile feelings of the operators, while
they are not conscious of the existence of delay. In touchingprocesses, spatio-temporal information such as temporal variations in the firing rates of the tactile mechanoreceptors, handmotions, and physical characteristics of target objects aremutually interlinked. A temporal disparity in the information
possibly changes the tactile feelings of the operators. If thisdisparity changes the feelings, it prevents the operators fromexperiencing the sensations as the developer of the display
systems intended.
The following tactile display systems must consider thepermissible system latency. The authors have proposed amethod that synthesizes tactile stimuli from the hand position, velocity, acceleration of the operators and the physicalproperties of target objects [1]. Other tactile display systems
also present tactile stimuli based on the measured handmotions [2-4]. These systems must be designed such that
their response time does not exceed the thresholds. A tactile
telepresence system is another example. The authors havealso proposed a tactile telepresence system that enables theoperators to touch remote objects in master-slave systems[5]. In remote environments, the tactile feedback from thetactile sensor includes the communication time-delay. It isnecessary to design tactile telepresence systems by taking
the permissible time-delay into account.
To the best of our knowledge, no studies on cutaneous
detection thresholds against the time-delay between input
actions and tactile stimuli have been reported. As a related
study, for designing virtual reality systems, detection thresholds of time-delays in other sensory channels have been
identified; - as summarized in table I. For auditory displayswith head movement trackers, detection thresholds of thetime-delay between the head movements and the presented
virtual sound sources were reported (45–80 ms) [6][7]. The
following thresholds also have been reported; the threshold
between the play motions of the operator and sound generation for virtual musical instruments (70–80 ms, calculated
from their report) [8], the threshold between typing motions
or mouse actions and graphical responses for graphicaluser interfaces (100–200 ms) [9], the threshold between

S. Okamoto, M. Konyo and S. Tadokoro are with Graduate School ofInformation Sciences, Tohoku University, 6-6-01, Aramaki-aza Aoba, Aobaku, Sendai-city, Japan, okamoto@rm.is.tohoku.ac.jp
S. Saga is with School of Engineering, Tohoku University

978-1-4244-1647-9/08/$25.00 ©2008 IEEE.

220

TABLE ID ETECTION THRESHOLDS OF TIME - DELAY FOR VARIOUS SENSORYCHANNELS AND INPUT ACTIONS

Sensory Channel
Auditory
Auditory
VisualVisualVisual and haptic

Input action
Head movement
Hand movement
Key type, mouse
Eye movement
Hand movement

Threshold [ms]45–80 [6][7]70–80 [8]100–200 [9]100 [10]30–35 [11]eye movement and image presentation for eye-movementtracking-type image displays (100 ms) [10] and the threshold
between visual and force feedbacks in presenting soft sphere(30–35 ms) [11]. They cannot be compared directly becausesome of the related studies employ different definitions forthe detection thresholds.
For force displays that are thought to be similar to
cutaneous sense displays in terms of time-delay effects
on the sensations, several studies have reported that thedelay impairs the task performances of the operators. The
permissible time-delay that does not disturb tasks for remote training or teaching with haptic interfaces [12][13],and the time-delay that decreases the quality of service
in collaboratively grasping and lifting objects in remoteenvironments have been identified [14]. The system latencyof force display against a hand movement possibly affects thesoftness discrimination[15]. These studies have investigated
how the delay influences task performances and have notfocused on the just noticeable time-delay for the operators.
The thresholds depend on the sensory channels and tasks.
The cutaneous detection thresholds against the time-delay
with hand motions as inputs and tactile stimuli as outputs
need to be identified by a specific method.
The disposition of the paper is as follows. Experimental
equipment and methods for identifying the two types ofdetection thresholds are described in section II. The experimental results are summarized in section III, and discussions
are presented in section IV. The conclusions are given in theend of this paper.
II. E XPERIMENT FOR I DENTIFYING T HE D ETECTION
T HRESHOLDS OF T IME - DELAY
A. Tactile Stimuli
This study addresses the presentation of virtual textures
as a task. The texture presentation is one of the typicalapplications for the tactile displays. The users explore andrecognize the textures through tactile displays.
The tactile stimuli are vibrations, which are fundamental
frequencies of the vibrations that occur to finger skins intouching the roughness scales whose spatial wavelength is λat velocity v. The vibratory stimuli are produced according
to the hand velocity. The voltage y supplied to the vibrator
was defined asv(t − D))+A
(1)
λwhere A is the amplitude of the voltages and it was 75 V.
D is the time-delay. The stimuli were produced using thebuffered velocity to simulate the system latency. In this study,
λ was 1 mm.
y = A sin(2πtB. Experimental System
Figs. 1 and 2 show the experimental equipment. Fig. 3
shows the block diagram of the entire system. The vibrator
was installed on a linear slider. Its position on the slider
was measured by a linear encoder whose spatial resolution
was 1.6 µm. A control computer received the encoder

Fig. 1. Experimental apparatus andan elbow rest for participants

Fig. 3.

Fig. 2. Schematic representation of
the experimental apparatus

Block diagram of the entire systempulses and supplied voltages to the vibrator. The control
frequency of the computer was 5 kHz. As a tactile vibrator,a piezo-stack-type actuator (NEC/TOKIN ASB510C801P0)
was adopted. The maximum indentation of the vibrator wasapproximately 60 µm for 150 V, and it was confirmed thatthe vibrator produced sufficient vibrations up to 300 Hz forgood perception.
The inherent time-delay of the system was measured 10
times; the maximum and median were 160 µs and 140 µs,
respectively. The inherent time-delay was the minimum delayof the system. It was defined as the period from the onsetof the encoder pulses to the resulting voltage changes in thevibrator.
C. Experimental Methods and Procedures
The participants were 13 males in their 20–30s. Eachparticipant touched the vibrator with his right middle finger
as shown in fig. 4. The participants were instructed not totouch any parts of their hands except their middle finger
to the vibrator and slider. The participants were blindfoldedand heard pink noise through a headphone. All the cues
during the experiment were beep sounds. Each participant
scanned the virtual object for 5 s after the first beep until
the second beep. With an interval of 3 s, the participant
scanned it again for another 5 s after the third beep until
the fourth beep. During the first 5 s, a stimuli with notime-delay was displayed, as a reference stimulus. During
the next 5 s, a stimulus whose time-delay was controlled
was displayed, as a test stimulus. During the experiments,
no true-false feedback was given to the participants. Fig. 5
shows the reference and test stimuli and an example of thehand velocity of the participant during one trial. Prior to eachtrial, the participants removed their finger from the vibrator
once and then placed it on again in order to prevent it fromparalysis. Within each trial, they tried to maintain contact

221

TABLE IIO BJECTIVES AND QUESTIONS POSED TO THE PARTICIPANTS IN
EXPERIMENTS A AND B

Objectives
QuestionsFig. 4. Experiment: Participant touched the vibrator with their right middle
fingerFig. 5. Example of the hand motion and simulated latency of the stimuli
in the trial

between their finger and the vibrator. The pressing force on
the vibrator was measured, and if it exceeded 2 N in the trial,
the trial was regarded as invalid and it was tested at the endof the experiment again. The participants practiced touching
and moving the vibrator with a force smaller than 2 N for
minutes. The encoder counts were recorded.
Two types of experiments (experiment A and B) wereconducted.
Experiment A aimed to identify the threshold for delay
detection. In experiment A, an experimenter explained to theparticipants that delayed tactile stimuli would be presented,
and the aim of the experiment was to identify the detection threshold against the time-delay. The participants wererequired to judge whether the test stimuli were delayed ornot.
Experiment B aimed to identify the threshold for detecting
the subjective changes caused by the time-delay. In experiment B, the experimenter explained to the participants thatsome parameters in the test stimuli might be changed slightly,
and the aim of the experiment was to investigate whether
the participants notice the changes. The experimenter did notgive them information regarding the types of parameters thatwere changed. The participants were required to determine
whether the test stimuli were the same as the reference
stimuli or were different.
The objectives and the questions posed to the participantsin the two types of experiments are summarized in table II.
Except for the prior explanations and questions describedabove, all the procedures were the same in experiments A
and B. All 13 participants were subjected to both the typesof the experiments with an interval of at least one day. Seven
subjects conducted experiment A at first, then experiment B

Experiment A
Identifying thethresholds for delay
detection
Delayed or not

Experiment B
Identifying the thresholds
to notice the tactile changes
caused by time-delay stimuli
Same or different

on different days. The remaining 6 participants conducted
them in reverse order. In order to prevent the preceding
experiment from affecting the subsequent one, experiment A
and B were conducted on different days for every participant.
Before each main experiment, a preliminary experiment
was conducted in order to estimate the time-delay D max
which the individual participant could always notice, by alimitation method. D max was in the range of 70–110 ms, in
26 experiments.
The main experiments were performed by a constantmethod; the standard stimulus was D = 0. D max was
equally divided into 6 stimuli between 0 ms, and one of
the 6 stimuli was assigned to D as the test stimulus. Each D
value was tested 10 times; the display order was random. One
experiment comprised 60 trials and it took approximately
40 min including the instructions, practices and preliminary
experiments.
In this study, both the reference stimuli (stimuli with notime-delay) and the test ones (controlled time-delay) were
presented to the participants in each trial. When both thestimuli were coupled, the participants became more sensitive
toward the changes in the signals than when the test stimuli
were presented individually; Brungart et al. reported thisobservation in their auditory tests[7]. The experiments wereplanned so that the participants remained sensitive; thisis because the identification of the maximum permissible
system latency is necessary for designing tactile display
systems.
III. E XPERIMENTAL R ESULTS
A. Method for calculation of detection thresholds
Fig. 6 outlines a method for calculating the thresholds inthis study. The vertical axis in the figure shows the ratio of
the positive answers. The horizontal axis shows the timedelay of the test stimuli. Examples of the positive answer
rates of the participant and a fitted curve f (D) are shown in
the figure. The fitting function is a logistic function definedasf (D) =

1
1 + exp (−a − bD)(2)where a and b are characteristic parameters of the curve.
The detection threshold is defined as D at which f (D) =0.5. DTA and DTB denote the detection thresholds of theparticipant in experiment A and B, respectively.

222

TABLE III
T EST RESULTS , COMPARING MEAN DTA AND DTB : TEST STATISTICS
AND p VALUES

t0 (p)
Whole samples (n=13)
Exclude outliers (n=12)
3.494 (0.00222)∗∗4.013 (0.00102)∗∗** significant at level 0.01

Fig. 6. Calculation method and the definition of the detection threshold:an example of the positive answer rates of the participant as a function of
the time-delay of the test stimuli

Fig. 8.
Scatter plot of DTA s vs. DTB s: There was no significant
correlation between DTA s and DTB s.

Fig. 7. Histogram of DTA s (thresholds identified through experiment A)
and DTB s (thresholds identified through experiment B)

B. Detection Thresholds of Participants
The histograms of the calculated thresholds of 13 participants in experiment A and B are shown in fig. 7. The
normal distribution curves of the threshold populations arealso shown in the figure.
Among 13 participants, DT A of participant ts might bean outlier ( Grubb’s test, G = 2.393 > G(0.05, 13) =2.331 ). Moreover, the false alarm rates of ts in bothexperiment A and B were 0.3, higher than those of theother participants. The authors considered the results of ts asoutliers and excluded them from any statistics. The means
and the standard deviations of the thresholds excluding ts
were DTA = 59.2 ± 13.0 ms and DTB = 40.9 ± 14.4 ms.
When ts was included, they were DT A = 55.6 ± 17.8 ms
and DTB = 39.4 ± 14.9 ms.
In the case of 12 participants, DT A of each participant
was larger than his DT B . The mean DT A was larger than
mean DTB with significant levels of 0.01 with or without
the outliers. Table III shows the results of paired t-test.
Fig. 8 is a scatter plot of DT A s and DTB s. There wasno significant correlation between DT A s and DTB s. (r =0.342, t-test, n = 12, two-tailed, p > 0.05, p = 0.273).
Two-way ANOVA was applied to the results. The factors
were the types of the experiments and the experimental order.
Fig. 9 shows the mean values of DT A s and DTB s with
their standard deviations; they are grouped on the basis of
the experimental order. The circles in the figure indicate
mean DTA s and DTB s of 6 participants who conducted
experiment A first. The rhombuses indicate the means of theFig. 9.
Mean DTA s, DTB s and their standard deviations by theexperimental order

other 6 participants who conducted experiment B first. Table
IV summarizes the analysis results. The type of experimentis the only significant factor that affects the thresholds. The
experimental order did not affect the thresholds.
C. Correlation between Detection Thresholds and Touch
Motions
Pearson’s correlation coefficients between the thresholds
and the feature quantities of the touch motions of theparticipants were calculated. Three types of feature quantities were used. The first one was the frequency of thereciprocating hand velocity. The power spectrum density of
the hand velocity of each participant was computed and thefrequency at which the power spectrum was the maximum

223

TABLE IV
T WO - WAY ANOVA SUMMARY OF THE DETECTION THRESHOLDS
FactorType of experiments
Experimental orders
Type × Order
Error

df
1
1
1
20

Mean Square Sum
1998.4
442.0
15.0
183.9

F
10.87
2.404
0.082

p
0.0036∗∗0.14
0.78

was considered the representative frequency of the touch
motions of the participant. The second one was the average ofthe peak speed in each half cycle of motions. The maximum
speeds of every half cycle of the reciprocating motions werecollected and their average was considered as the feature
quantity of the hand speeds of each participant. The thirdfeature quantity was the average of the peak accelerationin each half cycle of the hand motions. From the resultsof the test, it was observed that the frequencies and theaverage peak speeds exhibited weak correlations between thedetection thresholds.
Fig. 10 shows a plot of the relationship between the frequencies and the thresholds. The thresholds are normalized
in the figure, by dividing them by the mean thresholds inexperiment A or B. There was a negative correlation between
the 24 pairs of the thresholds and the frequencies (r =−0.541, t-test, n = 24, one-tailed, p < 0.01, p = 0.0032).
DTB s correlated with the frequencies ( r = −0.661, t-test,n = 12, one-tailed, p < 0.01, p = 0.0096 ), while DT A s did
not.
Fig. 11 shows a plot of the relationship between the hand
speeds and the normalized thresholds. There was a positive
correlation between the 24 pairs of the thresholds and thecorresponding speeds (r = 0.509, t-test, n = 24, one-tailed,p < 0.01, p = 0.0056). DTB s correlated with the hand
speeds (r = 0.561, t-test, n = 12, p < 0.05, one-tailed, p =0.029), while DTA s did not as in the case of the relationshipbetween the frequencies and the thresholds.
DTB s showed a negative correlation between the hand frequencies and a positive correlation between the hand speeds.
From these correlations, DT B s tended to be lower when theparticipants moved their hands with higher frequencies andsmaller strokes.
D. Subjective Tactile Feelings during the Trials
After the experiments, the participants were asked about
the subjective feelings. This section summarizes their major
opinions.
After experiment A, the experimenter asked the participants about how they detected the time-delay in the stimuli.
Their major answers were as follows; they recognized theexistence of the delay when they found no tactile feedback
at the onset of their motions, when the stimuli were still evenafter they stopped the motions, or when they felt the virtual
object unnaturally moved. They also reported that they feltthat something was moving beneath their hands.
After experiment B, the participants were asked about thechanges in their tactile feelings caused by the time-delay
stimuli (actually they were not given information about thetypes of parameters that were changed). Their answers wereas follows; they felt that the strength of the stimuli increased(rougher) or decreased (smoother), the weight of the slider
increased or decreased, or they felt frictional and viscous
resistance in their moving directions. It was observed thata simple time-delay tactile stimuli caused various changes
in the subjective feelings under the experimental conditionsof this study. Interestingly, contradictory opinions such as

Fig. 10. Frequency of the reciprocating touch motions vs. the detection
thresholds

Fig. 11. Average peak velocities of the reciprocating touch motions vs.
the detection thresholds

rougher and smoother were reported even from the same
participant.
IV. D ISCUSSION
A. Design Policy of System Latency according to the Objectives of Display Systems
The design policy of tactile display systems in termsof system latency is derived from the fact that there are
two types of cutaneous detection thresholds against timedelay. The permissible system latency varies according tothe objectives of the systems.
In the system that aims to present the textures of objects,
a threshold as small as 41 ms is a permissible delay. If thedelay is above this threshold, the perceived texture is most
likely altered. The users may not receive the tactile sensations
as the designer had intended to present.
In the system that aims to inform the users of the completion of their inputs to the system, a large threshold (59ms) is a permissible delay. For example, a display panelthat presents vibrotactile stimuli to show that a user presses
a virtual button on the panel, requires a time-delay thatis smaller than 60 ms. This is because the stimuli in thisapplication must be recognized as causal effects of the inputs
and the texture does not matter.
B. Difference between the Sensory Information Processes of
Two Types of Thresholds
There is a possibility that sensory information for latency
detection and the detection of tactile changes are processed224in different ways. The following two points suggest that thedifference of the sensory information processes in the two
experiments of this study.
First, from the observations of the participants in experiment A to detect the presence of latency, the authors findthat they took a longer time to answer the questions. On theother hand, in experiment B where the changes in their tactile
sensations are detected, they often answered immediately
even during the trial. From the differences between thenecessary times to answer the questions, in experiment A and
B the thresholds may be generated from different information
processes.
Second, as shown in section III-C, the thresholds for delay
detection were not correlated with the feature quantities of
the hand motions, whereas the thresholds for detecting thetactile changes correlated between the two feature quantitiesof the hand motions. This fact also suggests that the two
types of thresholds are influenced by different processes.
C. Relationships between Hand Motions and Thresholds for
Detecting the Tactile Changes Caused by Time-delay
As the hand speeds were small and the strokes were small,the participants were more sensitive to the changes in theirtactile feelings caused by the time-delay. These relationships
are interpreted as follows.
Because the tactile stimuli are produced based on (1),when the participant scans the object at a constant speed,
there is no change in the stimuli and the participant can
not notice the time-delay. As the participant’s hand speed isvaried, the time-delay produces the stimuli that are different
from the ones with no delay. With higher frequencies of thereciprocating hand motions, the stimuli are varied further andthe participants could more easily notice the tactile changes
caused by the time-delay.
Existing studies are consistent with the tendency that theparticipants were more sensible to the tactile changes when
the hand speeds were slow. Lederman has reported thatslower scanning slightly enhanced the perceived roughness[16]. Gamzu et al. have reported that the performances ofroughness discrimination tasks increased by training a certain
group of people to slowly scan roughness samples [17]. It is
possible that slower scanning improved the sensitivity of theparticipants toward the tactile changes caused by the timedelay.
V. C ONCLUSION
This study identified the two types of cutaneous detection
thresholds against the time-delay tactile stimuli through thepsychophysical experiments. In one threshold, the subjects
could notice the existence of system latency in the tactile
displays. This threshold was 41 ms. In the other threshold,the participants experienced changes in their tactile feelings while they were not conscious of the time-delay. This
threshold was 59 ms. It was observed that the simple timedelay stimuli caused various changes in their tactile feelings.
This study resulted in the development of a design policy
for the tactile display systems in terms of system latency.

The permissible system latency should vary according to theobjectives of the systems.
ACKNOWLEDGMENTS
The authors thank NEC/TOKIN for providing the vibrator
used as the tactile display in this study.
R EFERENCES[1] M. Konyo, A. Yoshida, S. Tadokoro and N. Saiwaki, A tactile synthesis
method using multiple frequency vibration for representing virtual
touch, Proc. 2005 IEEE/RSJ International Conference on Intelligent
Robots and Systems, pp. 1121-1127, 2005
[2] T. Nara, M. Takasaki, T. Maeda, T. Higuchi, S. Ando nad S. Tachi,
Surface Acoustic Wave Tactile Display, IEEE Computer Graphics andApplications, Vol. 21, No. 6, pp. 56–63, 2001
[3] V. Levesque, J. Pasquero, V. Hayward and M. Legault, Display ofVirtual Braille Dots by Lateral Skin Deformation: Feasibility Study,
ACM Transactions on Applied Perception, Vol. 2, No. 2, pp. 132–149,
2005[4] L. Winfield, J. Glassmire, J. E. Colgate and M. Peshkin, T-PaD: Tactile
Pattern Display through Variable Friction Reduction, Proc. The Second
Joint EuroHaptics Conference and Symposium on Haptic Interfaces for
Virtual Environment and Teleoperator Systems, pp. 421–426, 2007
[5] S. Okamoto, M. Konyo, T. Maeno and S. Tadokoro, Roughness
Feeling Telepresence System with Communication Time-delay, Proc.
The Second Joint EuroHaptics Conference and Symposium on Haptic
Interfaces for Virtual Environment and Teleoperator Systems, pp. 595596, 2007
[6] S. Yairi, Y. Iwaya and Y. Suzuki, Estimation of detection threshold ofsystem latency of virtual auditory display, Applied Acoustics, Vol. 68,
pp. 851–863, 2007
[7] D. S. Brungart, B. D. Simpson and A. J. Kordik, The Detectability of
Headtracker Latency in Virtual Audio Displays, Proc. The Eleventh
Meeting of the International Conference on Auditory Display, pp. 37–
42, 2005[8] T. Maki-Patola and P. Hamalainen, Latency Tolerance for GestureControlled Continuous Sound Instrument without Tactile Feedback,Proc. International Computer Music Conference, 2004[9] J. R. Dabrowski and E. V. Munson, Is 100 milliseconds Too Fast?,
Proc. Conference on Human Factors in Computing Systems, pp. 317–
318, 2001[10] K. Iwamoto and K. Komoriya, Permissible Time Delay for Image
Following in an Eye Movement Tracking Type Image Display System,
Proc. The 8th Conference on Intelligent Autonomous Systems ,pp.
889–906, 2004[11] M. Komori, R. Yoshida, T. Matsuda and T. Takahashi, User haptic
Characteristics Measurement for Design of Medical VR Applications,
CARS - Computer Assisted Radiology and Surgery, pp. 17-22, New
York, USA: Elsevier, 2000
[12] P. Dev, D. Harris, D. Gutierrez, A. Shah and S. Senger, End-to-End
Performance Measurement of Internet Based Medical Applications,
Proc. the 2002 American Medical Informatics Association Annual
Symposium, pp. 205–209, 2002
[13] K. Hikichi, Y. Yasuda, A. Fukuda and K. Sezaki, The Effect of Network Delay on Remote Calligraphic Teaching with Haptic Interfaces,
proc. 5th ACM SIGCOMM workshop on Network and system support
for games, Article no. 12, 2006[14] H. Nishino, S. Yamabiraki, Y. Kwon, Y. Okada and K. Utsumiya,
A Distributed Virtual Reality Framework for Korea-Japan HighSpeed Network Testbed, Proc. the 20th International Conference on
Advanced Information Networking and Applications, Vol. 1, pp. 433–
438, 2006[15] H. Ohnishi and K. Mochizuki, Effect of Delay of Feedback Forceon Perception of Elastic Force: A Psychophysical Approach, IEICE
Trans. Commun., Vol. E90-B, No. 1, 2007[16] S. J. Lederman, Tactile roughness of grooved surfaces: The touchingprocess and effects of macro- and microsurface structure, Perception& Psychophysics, Vol. 16, No. 2, pp. 385–395, 1974
[17] E. Gamzu and E. Ahissa, Importance of Temporal Cues for Tactile
Spatial-Frequency Discrimination, The Journal of Neuroscience, Vol.
21, pp. 7416–7427, 2001

225