Reaction Time to Vibrotactile Messages on Different Types of Soil
Landry D. Chapwouo T. and Bob-Antoine J. Menelas
Department of Computer Science, UQAC, University of Quebec at Chicoutimi (UQAC),
555 boulevard de l'Université, Chicoutimi, Quebec, Canada
Keywords: Haptic Messages, Reaction Time, Vibrotactile Message, Tactons, Foot Perception, Types of Soil.
Abstract: This study investigates the Reaction Time (RT) to vibrotactile messages presented under the foot plantar on
different types of soil. We determine whether reaction time varies while walking on different types of soil
(mobile situation). A total of six young participants (n=6) aged between 21 and 28 took part firstly in this
study where they had to walk on five types of soil (concrete, carpet, foam, gravel, and sand). The
methodology includes 360 repeated measures. The findings have consistently revealed a decrease of
reaction time to vibrotactile messages when walking on the three deformable soils (foam, gravel, and sand).
1 INTRODUCTION
With aging, many features that intervene in the
postural control decline (Hay et al, 1996; Teasdale et
al, 1991), it results that, the incidence of falls is over
30 percent per year for people over 65 years old
(Ganz et al, 2007). In this group of the population,
falls can cause physical injuries including fractures,
reduce functionality, admission to a nursing home
and sometimes death (Ménélas and Otis, 2014).
In this context, to prevent accidental falls we have
designed a system centred on an enactive shoe
(Ménélas and Otis, 2014) . Using an embedded
software, this system estimates in real-time the risk
level of accidental fall (low, medium, high and very
high). To inform the user about the computed risk,
we use a vibrotactile message presented under the
foot plantar. The usefulness of these messages relies
on two requirements. First, these messages have to
be correctly identified. For this a previous work
designed a serious game that allows users to
familiarize themselves with rendered vibrotactile
messages (have). Second, the messages should be
perceived rapidly. The current work address this
point by studying the reaction time (RT) associated
with the interpretation of these stimuli. If the RT
associated to such messages is too long, the user will
in fact not be able to adapt her/his balance.
RT plays a very important role in our lives as its
practical implications may be of great consequences.
Hyman mentioned that RT is a linear function of
stimulus information expressed in bits for the special
case in which response and transmitted information
are each equal to stimulus information (Hyman,
1953). Bricker proposes that the amount of
information an organism must process or transmit is
the crucial determinant of RT (Bricker, 1955). The
RT is a direct consequence of the time taken to
transmit the stimulus measured by the skin
mechanoreceptors along the nerve to the brain and
the response given to the neuromuscular system until
the first action of the muscles involved in postural
control. Psychologists have named three basic kinds
of reaction time experiments: Simple Reaction Time
(SRT), Recognition Reaction Time (RRT) and
Choice Reaction Time (CRT) (Bricker, 1955;
Kosinski, 2008). In a RRT situation, there are some
stimuli that should be responded to, others that
should get no response but there is still only one
correct answer. In CRT experiment, there are
multiple stimuli, and each stimulus requires a
different answer. Based on reaction time’s
definitions provided by (Kosinski, 2008), we will
situate our evaluation within the framework of a
reaction time (RT) because when there are only one
stimulus and one response (feeling or not) within a
walking process . Our methodology is concerned
with reaction time (RT) while walking in various
types of soil.
Prior to our study, there is no significant
traceable thread in the literature about evaluation of
the RT to a vibrotactile message under the foot while
walking on five different types of soil. We want to
T., L. and Menelas, B-A.
Reaction Time to Vibrotactile Messages on Different Types of Soil.
DOI: 10.5220/0006720301550161
In Proceedings of the 13th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2018) - Volume 2: HUCAPP, pages
155-161
ISBN: 978-989-758-288-2
Copyright © 2018 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
155
analyse the time needed to perceive a message sent
to the sole of the foot during walking. We
hypothesized that, RT, is greater when we have
more difficulty to walk on a type of soil. In other
words, RT depends on the types of soil. To this, we
want investigate the impact of RT to vibrotactile
messages presented on the foot when walking on
five types of soil.
The paper is organized as follows: in the second
section, we present related works, then follows the
third and fourth section where we present our
methodology with a full description of the
experiment. The obtained results are presented in the
fifth section and discussion follows in the sixth
section. Finally, we present conclusion and further
research in the seventh section.
2 RELATED WORK
In this section, we will analyze studies related to RT
in order to convey vibrotactile messages under the
foot plantar on different types of soil.
2.1 Reaction Time in Medical
Applications
RT has been extensively investigated for many years
in medical applications for instance to influence the
balance ability (Kosinski, 2008). Also, Reaction
time (RT) is one of the most important parameters
used in psychology to evaluate human tasks
(Kosinski, 2008). Various studies have measured the
fastest response time to the human touch at about
155 milliseconds (Edward S. Robinson, 1934;
Edward S Robinson, 1934; Welford, 1980).
Braverman et al. showed that a RT test is an accurate
predictor of early attention complaints and memory
impairments (Braverman et al, 2010). Moreover,
Gorus et al. showed that participants with cognitive
deterioration demonstrated more slowing RT than
healthy elderly (Gorus et al, 2008). Recently, Jain et
al. studied a comparison of visual RT (VRTs) and
auditory RT (ARTs) on the basis of gender and
physical activity levels of participants (Jain et al,
2015). Participants were asked to concentrate on the
fixation cross and press the “space bar” key, as soon
as possible once target stimulus appears on the
screen. They found a significant difference between
RT of male and female students. In addition,
significant results were found for the ARTs, which
were faster than the VRTs. It is known that the RT
has a direct impact on the risk of falling (Barr et al,
2014). For instance, Lajoie et al. investigated with
two groups (fallers and non-fallers) the possibility to
get a basic variable to predict the risk of falling
(Lajoie et al, 2002). Results showed that RT is an
interesting predictor of falling in the elderly, due to
the sensory and motor components associated. Given
that in everyday life, many falls occur on different
types of soil (Ayena et al, 2015; Otis et al, 2016) or
when walking on a stairway (Jackson and Cohen,
1995), the communication of a vibrotactile signal
could be influenced by the RT of the person as well
as the types of soil on which they are walking. The
literature highlights usability of SRT on medical
applications (balance impairment, auditory, and
visual task) but not the evaluation of a simple RT to
vibrotactile messages on the foot. As far as the RT
from different stimuli is concerned, the literature is
mature but, the above studies did not consider the
specific case that we are investigating here.
2.2 Foot Reaction Time
The need for tools to communicate information
under the foot on different types of soil has resulted
in some interesting initiatives for investigating foot
RT experiment and methodologies. Montés-Micó et
al. investigated the difference between the eye-hand
and eye-foot visual RT among young soccer players
versus non-soccer players (Jackson and Cohen,
1995). Eye-hand and eye-foot visual RTs were
determined by means of a computer-controlled
stimuli device. Results showed firstly that there are
statistically significant differences between eye-hand
and eye-foot RTs between players and non-players
of soccer. Secondly, the results demonstrated a fast
SRT time with soccer players. Recently, Mali et al.
conducted a study to compare Visual Reaction Time
(VRT) and Auditory Reaction Time (ART) of hand
and foot in young adults before and after physical
training (Mali et al, 2013). VRT and ART were
determined with the help of an electronic instrument
“Response Analyzer”. Results show that both VRT
and ART were significantly decreased in all four
limbs after physical training of six months. Pfister et
al. compared Reaction Response Time (RRT)
between hand and foot with a controlled devices for
medical application (Pfister et al, 2014). To evaluate
RT they assumed that, for physiological, anatomical
and ergonomic reasons, the time required to release
a switch with the hand is shorter than the time
required to release a switch with the foot. They
tested both the dominant and non-dominant hands
and feet by performing the “Kick-Test” for each
participant. Results demonstrate a significant faster
RT with the dominant extremity and Simple
HUCAPP 2018 - International Conference on Human Computer Interaction Theory and Applications
156
Reaction Time (SRT) test demonstrates significant
faster RT of the hands compared to the feet. All
these studies focused on foot RT, but not on the
case, which interests us here, namely, conveying a
risk level of falling under the foot plantar while
walking on different types of soil.
2.3 Reaction Time in Communication
of Information
It is known that many factors do affect RT
(Kosinski, 2008). RT has been widely used to
convey information, to test how rapidly stimuli
information can be processed and a response to it
can be activated (Luce, 1986). Some studies have
used SRT when work requires performance in a dual
task to assess the risk of falling. This paradigm is
called a probe RT. This is the case of Ming et al.,
they studied physical and cognitive factors
associated with falls by the elderly by evaluating the
probe reaction time (P-RT) (Hu et al, 2009). They
used a wearable trial tool, easy to use and useful for
the evaluation of the risk of falling and they discuss
the relationship when walking between simple RT,
probe RT and participant’s risk of falling. Results
showed that probe RT is useful for the evaluation of
the risk of falling and when the attention demands
while walking increase. Niemi and Näätänen stated
that a typical SRT includes many factors that can be
varied on several parameters: the warning signal
(WS), the foreperiod (FP), the reaction stimulus
(RS), the response (R), and the intertrial interval
(ITI) (Niemi and Näätänen, 1981). For instance,
Drazin evaluated the relationship between RT and
foreperiod (Drazin, 1961). Also, Peon and
Prattichizzo (Peon and Prattichizzo, 2013) studied
RT during conveying information by comparing
different sensory modalities (vibratory, auditory and
visual). Results showed that the haptic canal (strong
modality) can provide faster RT than the auditory
one.
These studies investigated the risk of falling by
evaluating SRT with various tools for
communicating information by the visual, audio and
haptic canals. However, these studies have focused
attention on RT in various conditions, with factors
like hand, finger, and foot. Obviously, they did not
assess the impact of the type of soil, nor the
evaluation of RT while walking (for mobile
application). The haptic canal can be used for RT
experiment, but in this study, we will use an RT
experiment to convey vibrotactile messages under
the foot aimed at alerting the user (De sa and
Carrico, 2011). Our approach differs in the sense
that we are planning to exploit the haptic modality to
convey information under the foot plantar on
different types of soil. This paper is intended to
evaluate the RT when transmitting a vibrotactile
message under the sole of the foot on different types
of soil.
To sum up, they are various applications of RT.
Several researchers have investigated the RT but
about the impact of RT vibrotactile messages on
various type of soil the literature still young. The
vibrotactile message in everyday life could be used
to inform the participant of important information
about a physical situation (in balance or not) or an
external environment (an alert). Moreover, in an
uncontrolled environment, people walk on different
types of soil without paying attention to the impact
of that type of soil on their balance. Their attention
is often occupied by a secondary task after walking.
Then, it is therefore important to investigate the
impact of types of soil affecting RT when conveying
vibrotactile messages while walking.
3 EVALUATION OF THE RT TO
VIBROTACTILE MESSAGE
The aim of this experiment is to evaluate the RT to a
vibrotactile message presented under the foot plantar
while walking on different types of soil.
3.1 Participants
Six young students from the University of Quebec at
Chicoutimi participated in the study. They were
recruited by means of a general invitation to
participate in a study related to the reduction of the
risk of fall. All the youths attended the session
voluntarily. The participants were aged from 21 to
28 (two female and four male). All were novices to
haptic technologies. For health issues, all
participants were instructed to wear socks and we
cleaned all components after each session. Before
the experiment, they were totally naive about all
aspects of the test and were given general
instructions concerning the task. All participants
follow up an interview including a questionnaire and
none of them reported any problem with foot
sensitivity. All volunteers involved in this study
were informed about the experimental protocol and
gave written consent before participating. The
experience and consent form had been previously
approved by the local ethics committee (certificate
number 602.434.01).
Reaction Time to Vibrotactile Messages on Different Types of Soil
157
3.2 Apparatus
Figure 1: Enactive insole: (a) signal amplifier; (b) Mark II
haptuator; (c) insole.
For this experiment, we use an enactive insole
developed in the laboratory (Fig.1.c). It consists of
an insole device equipped with two Mark II
Haptuators. The haptuator is a high-bandwidth,
iron-less, recoil-based electromagnetic vibrotactile
actuator (Ellis et al, 2011). It be driven as a common
loudspeaker. (Fig.1). The smartphone is fixed at the
ankle (Fig. 2). Measurements are performed between
60 to 362 Hz since the optimal response of the
vibration receptors (Pacinian corpusles) is reported
to be at frequencies between 10 500 Hz (De sa and
Carrico, 2011).
Figure 2: Positioning of the enactive insole on the foot: (a)
signal amplifier is fixed on the ankle; (b) Enactive insole
is wear into the shoe.
For the experiment, users have to walk on several
types of sole representing the natural flooring
surface materials that we commonly find in the daily
life: concrete, foam, carpet, sand, and gravel (Fig.
3). We have designed a longitudinal and wooden
partitioning device to accommodate selected sole
types (Length =5m, Width =1m Height =0.05m). We
filled each partition with real materials.
A set of four vibrotactile messages is proposed in
the experiment. They are based on the same rhythm
signal and duration of one second. They are
Table 1: List of equation of tactons.
Equation
Number
W
1
= a sin(2π121t)
(1)
W
2
= a sin(2π60t) sin(2π121t)
(2)
W
3
= a sin(2π3t) sin(2π121t)
(3)
W
4
= a sin(2π31t) sin(2π53t)
(4)
W
5
= 



(5)
W
6
= (-t
2
+ 0:5) sin(2π60t)
(6)
with t = (0: 1=9600: 1) sec.
3.3 Exploited Vibrotactile Messages
Figure 3: Types of soil. Left to right: (a) Concrete, (b)
Carpet, (c) Foam, (d) Gravel, (e) Sand.
designed according to various studies of
psychophysical perception reported in (Visell et al,
2009) and (Menelas and Otis, 2012). The waveform
of each vibrotactile message is described by
equation (Table 1). W
1
defines a pure sinusoidal
wave (121 Hz). W
2
is an amplitude modulation of
W
1
by 60 Hz of pulsing vibration. W
3
is a
modulation of W
1
by a 3 Hz sinusoid of rapid
impulse vibration. W
4
is a 53 Hz sinusoid modulated
by a 31 Hz of rough vibration sensation. W
5
is a
Gaussian function where a, is the amplitude of the
signal, e is the Euler number, b is the position of the
center of the peak, and c adjust the bandwidth of the
function. W
6
is a sinusoid modulated by a quadratic
function providing an increasing or decreasing
tactile sensation.
4 EVALUATION OF THE RT TO
VIBROTACTILE MESSAGES
At the beginning of the experiment participants are
seated, wearing an ear protection and the enactive
HUCAPP 2018 - International Conference on Human Computer Interaction Theory and Applications
158
insole on the left foot. They are then invited to select
four among the six vibrotactile messages. Thereafter
the evaluation starts.
Participants have to walk on the 5 types of soil
(Fig.3). Three trials are needed on each soil. For
each trial selected messages are randomly conveyed
under the foot plantar. Doing so, 360 repeated
measures (6 participants x 5 types of soil x 3 trials x
4 messages) are performed.
Whenever the participant perceives a message
he/she is instructed to lift the foot as quickly as
possible. The RT is computed by calculating the
acceleration of the foot movement. The
accelerometer attached to the foot is used to
determine the real time of the stimulus perception
through the speed of movement of the foot. The
acceleration (m/s2) was recovered on the three axis
x, y, z and was compared with an acceleration
threshold value. If the value of the acceleration on
one axis were equal to the threshold, the
identification time (t
2
) would be saved and we would
compute the RT with the initial time of the stimulus
conveyed (t
1
): RT
i
= t
i2
t
i1
where i represents one
vibrotactile message on a type of soil. If the
vibrotactile message is not perceived after the
maximum time of 5 seconds, then the signal is sent
back.
The overall time is 45 minutes with a break of 5
minutes between the two steps.
A semi-directed interview with Likert-based
question was conducted. In our post-experimental
interview, we asked participants the following
question: What do you think might be the level of
risk for each soil according to your RT to this soil?
This question was intended for user’s experience
about the comprehension, and explanation of RT
data analysis on different types of soil.
5 RESULTS AND DISCUSSION
All participants went through the experiment
successfully.
Table 2: Mean RT in milliseconds by participants in each
type of soil.
Participants
Concrete
Carpet
Foam
Gravel
Sand
A
312.5
330
330
365
347.5
B
252.5
320
397.5
527.5
587.5
C
492.5
472.5
492.5
365
907.5
D
420
445
530
777.5
710
E
490
487.5
460
545
665
F
372.5
405
460
470
450
390
410
445
508.33
611.2
SD
96.56
71.64
71.29
152.79
198.2
5.1 Vibrotactile Messages Preference
Observed results provide a general indication on the
preference of participants on the set of haptic
messages proposed to convey a risk level under the
foot. Among the six vibrotactile messages presented,
participants had to select four and then. The results
(Table. 2) show that the participants had a similar
preference in the choice of vibrotactile messages.
We observed, for the four risk levels of falling low,
medium, high, and very high, participants have
generally associated vibrotactile messages W
6
, W
2
,
W
1
, and W
3
respectively.
5.2 Observed Reaction Times
Individual results showed that the smallest RT was
252.5 msec. observed for the participant B on the
Concrete soil. The highest RT was 907.5 msec.
observed in participant C on the Sand soil. Mean RT
results are found in (Table 2). On average, the fastest
RT can be observed on the Concrete soil (390 msec.)
and the slowest RT is observed on the Sand soil
(611.25 msec.). All these results revealed that the
RT varies according to the types of soil.
We also analyzed conditions for which
participants did not perceived the vibrotactile
messages. In general, five (5/6) participants did not
perceive the vibrotactile messages on three types of
soil (Foam, Gravel, and Sand). The breakdown is as
follows: (3/6) concerning the Foam, (4/6)
concerning the Gravel and (4/6) concerning the
Sand. On the other hand all participants were able to
identify vibrotactile messages on the Concrete and
Carpet types of soil. The results also showed the
mean RT were different according to the type of
soil.
Table 3: Additional statistic test.
Soil pair
Type of test
P-value
Concrete - Sand
Tukey
0,04
Concrete - Sand
Bonferroni and
Holm
0,02
Concrete - Sand
Fisher
0,034
Sand - Concrete
Fisher
0,006
Sand - Carpet
Fisher
0,012
5.3 Statistical Analysis
We performed an ANOVA with repeated measure
on the mean RT (Table 3). Factors are the types of
soil and its associated levels are Concrete, Carpet,
Foam, Gravel, and Sand. Our assumption for the
ANOVA was the homogeneity of variance, we
supposed that variance in different levels of each
x
Reaction Time to Vibrotactile Messages on Different Types of Soil
159
independent variable was equal. The significance
level (α) is 0.05. The p-value corresponding to the F-
statistic of ANOVA (F(4, 25) = 2.92, p < 0.05) was
lower than 0.05, suggesting that the one or more
mean RTs across types of soil were significantly
different. To identify which of the pairs of soil are
significantly different from the others, the Tukey
HSD test, Bonferroni and Fisher's least significant
difference (LSD) were performed. Results of these
additional tests are reported in Table 3. We can
observe that the pairs 1, 2, 3 are significant from
each other. Thus, we can reject the null hypothesis
and confirm the alternative hypothesis. No other
statistically significant difference was found, but
from data collected in our post-experimental
interview, a simple contrasts indicated that
vibrotactile RTs were much longer for soft or
irregular surfaces according to the rank ordering of
the surfaces causing concerns in Table 4.
Table 4: Types of soil causing perception difficulties.
Level of difficulty
Type of soil
Low
Concrete
Carpet
Medium
Concrete
Sand
High
Foam
Sand
Very high
Gravel
Sand
Additional question on the survey about the
device revealed that 66.66% of the population feel
uncomfortable with the device while walking.
5.4 Discussion and Limitations
Overall results suggest a significant effect of type of
soil on RT to vibrotactile message. The factors that
most influence the RT to a vibrotactile message is
when participants walk on the Sand and on the
Gravel.
Vibrotactile RTs were longer on deformable
surfaces. A possible explanation for that is that when
walking the pressure exerted on the surface induces
deformations that introduce perceptual conflicts in
the understanding of proposed haptic messages. As
result, vibrotactile messages are thus better
perceived on non-deformable soils (Concrete,
Carpet) when compared to deformable ones (Foam,
Gravel, and Sand). Moreover, based on, our post-
experimental interview, we observed that most
participants (83.33%) had experienced some
difficulties to walk on these soils. They categorized
them as types of soil with very high-risk difficulty
(Table 4).
The main limitation of this study concerns the
participants; it focuses on two aspects that will be
investigated in future work. The first is related to the
limited number of participants in the study.
Although we had significant results, the sample
being very small, it will be important to repeat the
experiment with more subjects. The second
limitation concerns the representativeness of the
sampling. The purpose of this study was to validate
the possibility of using vibrotactile feedbacks to
transmit messages under the foot plantar during
walking. This step now taken, we will need to
validate this possibility with the population targeted
by the designed instrumented footwear (Menelas and
Otis, 2012). More particularly, we will have to
experiment with the possibility of use and perception
of these messages with elderly people.
6 CONCLUSION
This paper aimed at evaluating the RT to vibrotactile
messages when walking on five types of soil. We
analysed the time needed to react to a vibrotactile
message sent to the foot plantar, using an enactive
sole, while walking. Two main results have been
noted. First, we observed that the RT was
significantly longer on deformable surfaces
compared to non-deformable surfaces. Second,
results and answers to the post-experiment interview
showed that the information (the risk of falling)
conveyed through vibrotactile messages is better
perceived on non-deformable surfaces. It thus
appears that types of soil can influence the
perception when walking. But, to increase the
significance of our results, an extension of this work
will be to use an apparatus adapted to improve the
user experience when walking, increases the number
of participants (fallers and non-fallers / youth and
elderlies), and finally study the positioning of the
Haptuator on the body.
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