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Finding the Minimum Perceivable Size of a Tactile
Element on an Ultrasonic Based Haptic Tablet
Farzan Kalantari, Laurent Grisoni, Frédéric Giraud, Yosra Rekik
To cite this version:
Farzan Kalantari, Laurent Grisoni, Frédéric Giraud, Yosra Rekik. Finding the Minimum Perceiv-
able Size of a Tactile Element on an Ultrasonic Based Haptic Tablet. ISS ’16, 11th ACM Interna-
tional Conference on Interactive Surfaces and Spaces, Nov 2016, Niagara Falls, ON, Canada. pp.6,
�10.1145/2992154.2996785�. �hal-01381314�
Finding the Minimum Perceivable
Size of a Tactile Element on an
Ultrasonic Based Haptic Tablet
Farzan Kalantari
University of Lille 1 - Science
and Technology
CRIStAL, INRIA Lille
Villeneuve d’Ascq, France
farzan.kalantari@inria.fr
Yosra Rekik
University of Lille 1 - Science
and Technology
INRIA Lille
Villeneuve d’Ascq, France
yosra.rekik@inria.fr
Laurent Grisoni
University of Lille 1 - Science
and Technology
CRIStAL, CNRS, INRIA Lille
Villeneuve d’Ascq, France
laurent.grisoni@univ-lille1.fr
Fr´ed´eric Giraud
University of Lille 1 - Science
and Technology
L2EP, CNRS
Villeneuve d’Ascq, France
frederic.giraud@univ-lille1.fr
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ISS '16, November 06-09, 2016, Niagara Falls, ON, Canada
ACM 978-1-4503-4248-3/16/11.
http://dx.doi.org/10.1145/2992154.2996785
Abstract
Tactile devices with ultrasonic vibrations (based on
squeeze film effect) using piezoelectric actuators are one
of the existing haptic feedback technologies. In this study
we have performed two psychophysical experiments on an
ultrasonic haptic tablet, in order to find the minimum size
of a tactile element on which all the users are able to
perfectly identify different types of textures. Our results
show that the spatial resolution of the tactile element on
haptic touchscreen actually varies, depending on the
number and types of tactile feedback information. A first
experiment exhibits three different tactile textures, chosen
as being easily recognized by users. We use these textures
in a second experiment, and evaluate minimal spatial area
on which the chosen set of textures can be recognized.
Among other, we find the minimal size depends on the
texture nature.
Author Keywords
Haptic; Tactile device; Friction modulation; Ultrasonic
vibrations; Minimum size; Texture rendering.
ACM Classification Keywords
H.5.2 [User Interfaces]: Input devices and strategies.
Introduction
Eye and ear are used by humans for retrieving most of
information in the real, physical, world; both sense
channels are quite well handled by technology. But the
sense of touch in human is still complex and varies on
different people and is not an absolute phenomenon. The
tactile information perception might be influenced by
environmental conditions such as temperature and
strongly based on the skin mechanoreceptors of the
human finger. Therefore the existing interactive
technologies allowing to provide user to retrieve
information through tactile sense are still emerging and
many parameters appear to make it difficult for
applications to handle tactile feedback in a shared, generic
way. In particular, each tactile technology still demands a
specific development and adaptation [13].
In the field of technologies for visual feedback, the concept
of pixel had a huge consequence on display technology
and provides a conceptual common basis between higher
level software architectures, and lower-level, electronic
systems that is used for display. Such common concept is
still missing for tactile feedback; we still lack a common,
shared reference of an elementary tactile information,
both in terms of spatial resolution, and information
nature; can we go up to a normalization level comparable
to the one that pixels provide for visual information?
In this study we introduce a step toward the concept of
taxel (Tactile Element), by suggesting an up-down
response protocol (adaptive procedure) in psychophysics
[5] that allows, for a specific tactile feedback technology,
to measure the minimum size on which tactile information
can be retrieved. We define the notion of texture
waveform as the elementary signal shape that we provide
to the tactile feedback technology, that is used as
periodical signal for tactile stimulation. Such notion is a
standard, usable term for all existing tactile feedback
technologies (see related work section). We provide a first
experiment that identifies few elementary textures that
can be easily identified by user. Among the 24 textures
proposed to user, we identify three that all users can
identify accurately. From this experiment, we derive a
second experiment that evaluates the minimum size of the
tactile element at which user can differentiate textures
accurately. We conclude that the texture type influences
the minimum size of the tactile element.
Related Work
In the recent years, touchscreen interfaces with haptic
feedback to the user’s finger have become more and more
popular.This haptic feedback permits the users to enrich
the feeling of what they touch and can improve the
performances of their interactions.[3, 6, 14]
Generally, we can divide the haptic feedback technology
on touchscreen interfaces in to 4 categories. These
technologies mostly use various friction modulation
between the fingertip and the interaction surface for
texture rendering. The first class of devices are based on
electro-vibration effect which use electrostatic force,
generated by applying a voltage to the surface for haptic
feedback [2, 8]. The second category create haptic
feedback through electroadhesion technique, which also
use electrostatic force generated by DC excitation to the
haptic surface. [9]. Both of these two classes of devices
increase the friction between the fingertip and the
interaction surface. The third class of devices are based
on friction reduction using ultrasonic vibration via the
squeeze film effect [1, 12, 7]. This effect reduces the
friction, which is opposite to electrostatic force in the two
previous technologies. The fourth class of devices utilize
vibrotactile actuators for tactile rendering which is widely
used in smartphones and tablets since several years now
[4]. Furthermore, in [10] the differences in haptic
perception of object size when exploring the inside or
outside the objects is investigated by means of
psychophysical experiments. But there is still no studies
to show the minimum object size for tactile perception
while using a touchscreen device with haptic feedback.
Experiment 1: Finding the Three Perceivable
and Distinguishable Textures
At first we have done an experiment in order to find at
least 3 different textures that could be perceived and
distinguished properly by all users. We have selected 3
types of textures due to the time constraints for
performing the two experiments by participants.
Apparatus
We used a haptic tablet based on ultrasonic vibrations for
texture rendering [11] which is developed on a Banana Pi,
a single-board computer with 1 GHz ARM Cortex-A7,
dual-core CPU and 1 GB of RAM working in parallel with
STM32f4 microcontroller. The communication between
the singleboard computer and the microcontroller is
provided via the Serial Peripheral Interface (SPI) bus at
10 kHz. This singleboard computer is connected to a 5
inches capacitive touchscreen in order to detect the finger
position on the display with the sampling frequency of 50
Hz. The two piezoceramic actuators are placed at each
side of the display.
Design and Procedure
In order to design our first experiment, we have defined 4
types of texture waveforms as square, sine, dirac and
sawtooth with the constant amplitude of 1 µm and the
spatial frequencies of 50 µm , 100 µm, 500 µm, 1000 µm,
5000 µm and 10000 µm. The setup of the first
experiment is illustrated in figure 1 which was coded with
Java and Processing language and the display is divided to
4 equal sections. On each part there is a specific texture
waveform and so the value of spatial frequency can be
selected. Ten participants (4 female and 6 male) were free
to explore the surface as long as they wanted and then
choose 3 or 4 textures that could be accurately sensed
and distinguished among all the 24 provided textures.
Figure 1: The setup of the Experiment 1
Results
The analysis of results as we can see in table 1, show that
several participants could distinguish between 5 to 7
different textures. In overall the results demonstrate that
all 100% of participants could perceive and distinguish the
following textures perfectly: square texture, sinusoidal
texture and dirac texture with the spatial frequency of
50 µm, 1000 µm and 1000 µm respectively and the
constant amplitude of 1 µm for all of the textures. The
feeling perception of the dirac and sawtooth texture
waveforms were more or less similar for the participants
and therefore rather hard to be distinguished appropriately.
These results are used for our second experiment.
Participants Square (µm) Sinusoidal (µm) Dirac (µm) Sawtooth (µm)
1 50 1000 1000 5000
2 50 1000 1000 10000
3 50 1000 1000 5000
4 50 500,1000 1000 500,1000,5000
5 50,1000,5000 1000 1000 5000
6 50,1000 500,1000 1000 5000,10000
7 50,1000 500,1000 500,1000 10000
8 50,1000 1000 500,1000 10000
9 50 1000 500,1000 1000
10 50 1000 1000 10000
Table 1: The results of the chosen textures from experiment 1
Experiment 2: Finding the Minimum Size of
a Tactile Element
The goal of our second experiment is to determine the
minimum size of a tactile element (taxel) on the
touchscreen on which the participants are able to
distinguish the 3 textures found from the results of the
experiment 1. As before we have used the same haptic
tablet based on ultrasonic vibrations and defined 3
textures due to the time constraints to accomplish the
task by the participants
Figure 2: The setup of the minimum size experiment
The participants were demanded to find the accurate
corresponding texture of the first taxel among the 3 other
taxels and clicked on (1), (2) or (3) on the keyboard for
the correct answer.
Design and Procedure
We have used an up-down response protocol (adaptive
procedure) in psychophysics [5] with the total number of
25 tries for each of 3 trials. Thus the minimum size of the
tactile elements is considered to be the last size as the ten
participants obtained after 25 tests for each trial (10
participants × 3 textures × 25 times = 750). We have
displayed 4 tactile elements of square shapes with the
identical initial size of 10 mm (1cm) that are situated in
parallel as shown in figure 2. At each try if the
participants has a correct answer for the texture detection,
the size of all squares decrease by 0.5 mm simultaneously
and for the wrong answers it will increased by 0.5 mm. At
each step there is a specific texture on the first tactile
element and the textures on the other taxels are assigned
