TACTILE GUIDANCE OF THE HAND IN A BLIND POINTING

TASK: “THE TACTILE COMPASS”

Tactile Compass in a Blind Pointing Task

M-C. Lepelley, L. Lejeune, F. Thullier, E. Faugloire and F. G. Lestienne

ERT 2002 « Rapsodie », EA 4260 IOA, MODESCO UMS 843 CNRS, Université de Caen Basse-Normandie, France

Keywords: Vibrotactile device, Tactile compass, Spatial guidance, Directional prescriptors, Pointing task.

Abstract: Using tactile skin receptors that are sensitive to vibrations thereby allowing the use of a “tactile compass”

made up of a matrix of micro-vibrators that reproduce tactile encoding on the skin surface to orient the

wearer. The tactile compass used in this study consisted in 49 microvibrators laid out in a 7x7 matrix. The

49 microvibrators contained inertial vibrators activated by micromotors. The tactile messages were provided

in a dynamic way by the successive activation of each microvibrators. The present study investigated the

efficiency of the tactile compass in guiding the hand in a blind pointing task when inserted into an

abdominal girdle. More specifically, the performances obtained using tactile coding are compared to those

obtained using verbal instructions. The participants had to point, from the central target towards one of the

four other targets each corresponding to one of the six directions (upwards, downwards, left, right,

backwards and forwards) located either in the frontal plane or in the horizontal plane. Overall, the results

reveal the efficiency for gesture guidance of providing tactile messages in a dynamic way, without

involving learning. In addition, they establish that tactile information transmitted via our vibrotactile device

is involved in the processes of both motor control and production of movement in tridimensional space.

1 INTRODUCTION

The tactile compass is based on the well-known

clinical test of “skin writing” which consists in

tracing different characters (letters or digits) on the

body surface of the subject. If this test can reveal

changes at the level of tactile receptors, as well as

changes in the central nervous system (CNS) at low

level, by contrast, the tactile compass test can yield

valuable data about mechanisms underlying

perceptual and gnostic functions at a higher level of

the CNS (Natsoulas and Dubanoski, 1964; Caffara et

al., 1976; Parsons and Shimojo, 1987; Gurfinkel et

al., 1993).

Taking into account that: (1) localisation of the

skin’s mechanoreceptors is quite well represented in

the CNS (Phillips, 1988), (2) the brain’s processing

of the tactile signal is characterised by a high level

of sensitivity, acuity and rapidity (Johansson et al.,

1982; Johnson and Phillips, 1981), the

vibrostimulation of the skin is a useful way to

present information in tactile form, instead of

visually or in auditory form (Bliss et al., 1970;

Jagacinski et al., 1979).

The use of a “tactile retina” as a substitute of the

retina of the eye in the blind has been extensively

studied over several years. For example, early

pioneering work in the Tactile Vision Substitution

System (TVSS) was performed by Paul Bach-y-Rita

and colleagues in the late 1960s. The TVSS

displayed visual information captured by a tripod

mounted TV camera to a vibrotactile display on the

user’s back (Bach-y-Rita, 1982, 2004).

According to the ‘tap-on-the-shoulder’ principle

(Van Erp, 2005), vibrotactile devices consisting in

fitting vibrating elements to various body locations

allow spatial guidance (Lepelley et al., 2005;

Lepelley, 2008). Among successful applications

with relatively simple displays is Van Erp’s device,

which presented directions from an in-car navigation

system by means of vibrating elements located under

the left and right legs (Van Erp and Van Veen,

2004). In the same vein, we have to mention the

studies of Rochlis and Newman (2000), who

presented directional information during simulated

214

Lepelley M., Lejeune L., Thullier F., Faugloire E. and G. Lestienne F. (2010).

TACTILE GUIDANCE OF THE HAND IN A BLIND POINTING TASK: “THE TACTILE COMPASS” - Tactile Compass in a Blind Pointing Task.

In Proceedings of the Third International Conference on Bio-inspired Systems and Signal Processing, pages 214-219

DOI: 10.5220/0002709902140219

 SciTePress

extra-vehicular activity in space by means of

vibrating elements located on the torso and the neck.

More complex displays, consisted in 60 (or more)

vibrating elements covering the entire torso of the

user. These torso displays present not only the left

and right directions, but also map eight or more

external directions in the horizontal plane.

This paper is devoted to investigating the

efficiency of a prototype of vibrotactile device called

the “Tactile Compass” (TC), which is inserted into

an abdominal belt, in perception and identification

of tactile stimuli to convey appropriate spatial

information. More precisely the TC, consisting in a

7x7 matrix of micro-electromechanical vibrators,

provides tactile messages in a dynamic way. The

trajectory and duration of the vibration was designed

to develop tactile semantic encoding prescriptors

such as directional, kinetic and kinesiological ones.

The present study investigated the efficiency of

the TC in guiding the hand during a pointing task.

More specifically, in a blind experiment, the

performances obtained using tactile encoding focus

on the directional prescriptors are compared here to

those obtained using verbal instructions.

2 METHODS

2.1 Apparatus

The vibrotactile device (Caylar Society ©)

consisted in 49 microvibrators (called “pins”) laid

out in a 7x7 matrix (Figure 1), a power unit, a micro-

control unit MIcroship (PIC16F688) and a connector

serial port.

Figure 1: Prototype of the tactile compass (TC) (Caylar

Society ©). Localisation of the centre of the TC was 50

mm above the ombilic.

Each pin consisted of an inertial vibrating

element (VE) activated by micromotors (2 mm in

diameter) based on classic technology. The shape of

the VE was designed to have a conic section with a 1

square millimetre skin contact area. The distance

between each pin was 6 mm. The oscillation

frequency of the pins was 50-60 Hz with a

magnitude of 2 mm. The 7x7 pins were mounted in a

small PVC box with a square area of 63 mm. To

ensure proper vibrational reception in each pin and

to minimize the lateral propagation of the vibration,

each pin was housed in a Plexiglas honey-comb

specifically manufactured for this. The pin was

glued to the cell by means of synthetic latex.

In the inactive state, all the 49 pins were in

contact with the skin. In the active state, the tactile

messages were provided in a dynamic way by the

successive activation of each pin.

The TC was mounted in an adjustable abdominal

belt. The locations of the TC in the belt were also

adjustable so that they could easily be positioned

regardless of the subject’s body form.

2.2 Software of the Micro-Control Unit

(MCU)

During tactile stimulus presentation, the pins were

arranged in sequence to form the desired tactile

pattern. For each pin, the duration (d) of activation

of each pin and the time interval (t) between the

activation of successive pins were specified using

the control library of the MCU (see Figure 3).

2.2.1 Pin Mapping

The MCU and the data collection software were

written entirely in C++.

The MCU software is targeted primarily for use

in an operating system that specifies the following

by means of the control library of the MCU:

-the position of each pin individually in a Cartesian

(x, y) plane (Figure 2 and the upper part of Figure

3), the individual pins being numbered from 1 to 49;

-the temporal characteristics (upper part of figure 3)

of activation: duration (d) and time interval (t)

-pre-specified patterns of pin movement (bottom

part of Figure 3).

TACTILE GUIDANCE OF THE HAND IN A BLIND POINTING TASK: "THE TACTILE COMPASS" - Tactile

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Figure 2: Schematic diagram of the generation of pin

activation in a Cartesian plane (x, y).

2.2.2 Alpha-Numeric Screen

The alpha-numeric screen displays the control

library that converts tactile prescriptors (directional,

kinetic and kinesiological) provided by the

experimenter into voltages that drive each of the 49

pins.

Figure 3: Overview of the alpha-numeric screen (see

explanations in the text).

The upper part of the screen is an illustration of

the sequential commands used to form the desired

“tactile” character “9”. In this example the duration

of the drawing of “9” was 1500 ms with d=100ms

and t=0ms.

The bottom part of the screen depicts 40 pre-

specified tactile patterns used as tactile semantic

encoding tactile prescriptor:

-Directional prescriptor: Upwards, Downwards,

Right, Left, Forwards, Backwards…

-Kinetic prescriptor: Stop, Accelerate, Brake…

-Kinesiological prescriptor: Ascend, Descend,

Turn...

2.3 Protocol

2.3.1 Subjects

Twelve young subjects (6 males and 6 females)

(29.23 ± 3.2 years) were tested in this study. They

were all right-handed as ascertained according to the

hand they preferred to use when writing and eating.

They were recruited among students of Caen

University. They had never participated in a tactile

perception task.

All subjects gave informed consent to take part

in the experiment according to the institutional

procedures of our university.

2.3.2 Task and Experimental Procedure

During a familiarization phase, the participants had

to point from the central target towards one of the

four other targets, each target corresponding to one

of the six directions (upwards, downwards, left,

right, forwards and backwards) (Figure 4C and 5)

located either in the frontal plane or in the horizontal

plane (Figures 4A and 4B). In a test phase, the

directional targets were removed and the participants

had to point at the target, the direction of which was

provided by either tactile instructions (on the

abdomen) or verbal instructions. Both types of

instruction (tactile and verbal) and types of plane

(horizontal and frontal) were counterbalanced across

participants.

Figure 4: Schematisation of the two planes of the pointing

task (A: frontal plane, B: horizontal plane) and of the

positions of the targets (C).

Kinematic data were analysed to measure the

precision and the velocity of the pointing task. For

this purpose a motion capture system (Vicon MX-

40, Oxford Metrics Ltd) including 4 cameras with

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Figure 5: Experimental setup (on left), display of the 9

markers during pointing to the central target.

100 Hz visual sampling frequency allowed us to

record the 3D position of 9 markers located on the

fingertip, wrist, elbow, shoulders, hips and head

(Figure 5).

3 RESULTS

The results support the proven effectiveness of TC

in tactile guidance of the hand during a blind

pointing task. The level of performance halfway

between chance and perfect performance has

therefore been clearly reached. Indeed, the

participants identified 93.27 % of tactile directions

(Figure 5). Moreover, no significant effect of type of

instruction (verbal versus tactile) on the number of

correctly identified directions (χ2 = 1.18; ddl = 1;

ns) was noticed. Similarly, no significant interaction

between type of instruction and precision of pointing

(F(1,10) = 0,96 ; ns), nor between type of instruction

and variability of pointing (F(1,10) = 1,24 ; ns) were

noticed.

In addition, no significant effect of type of

instruction was found in the kinematic data (mean

velocity (F(1,10) = 0.28; ns); planes of motion

(F(1,10) = 0.002; ns). Consequently, the prototype

Figure 6: Percentage of correctly identified directions for

verbal and tactile instructions.

provides information about direction that is at least

as well perceived as verbal instruction, and does so

without disturbing the spatio-temporal organization

of the movement.

It is of interest to notice in Figure 7 that pointing

was faster in the horizontal plane than in the frontal

plane (F(1,10) = 6.44; p < 0.05).

Figure 7: Mean velocity in mm.s

-1

for horizontal (blue)

and frontal (red) planes during pointing.

Furthermore, the precision of pointing was better

in the frontal plane than in the horizontal plane

(F(1,10) = 6.59; p < 0.05). The mean deviations

were greater in the horizontal plane than the frontal

plane (F(1,10) = 39.52; p < 0.05). These results are

in agreement with those obtained by Ghafouri and

Lestienne (2006), which showed an under-

representation of horizontal egocentric space in the

internal representation of space.

Figure 8: 3D constant error (left) and mean deviations

(right) for horizontal (blue) and frontal (red) planes during

pointing in mm.

4 DISCUSSION

Overall, the results of this study reveal the efficiency

of providing tactile messages in a dynamic way.

TACTILE GUIDANCE OF THE HAND IN A BLIND POINTING TASK: "THE TACTILE COMPASS" - Tactile

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217

Indeed, the present experiment confirms that

subjects are able to indicate an external spatial

orientation that matches successive vibrotactile point

stimulus on a small surface (63x63 mm

) of the skin

of the abdomen. The tactile discrimination between

the six directional prescriptors results in remarkably

robust similarities across the 12 subjects. In other

words, this study showed that a localized vibration

on an abdominal belt could easily and accurately be

interpreted as a direction in the horizontal and

frontal plane and can be used to signal multi-

directional motion and to guide hand movement.

Through these initial empirical findings, the results

confirm that the skin surface of the human body

(hand, arm, leg, neck, torso, abdomen) is very

sensitive to temporal aspects of vibrotactile

stimulation (Gurfinkel et al., 1993; Van Erp and

Werkhoven, 2004; Lepelley et al., 2005; Lepelley,

2008; Asseman et al., 2008).

The primary goal of the present study was to

gain insight into the characteristics of generation of

the tactile message. Consequently, we tested the

appropriate spatial and temporal resolution of the

tactile pattern (see appendix) to generate the tactile

semantic encoding:

a)-distance between each pin: 6 mm,

b)-vibration frequency: 50-60HZ,

c)-activation time (d) of the pin: 200 ms,

d)-step time (t) between the activation of successive

pins: 150 ms.

It is of interest to stress that the precision of

pointing was better in the frontal plane than in the

horizontal plane. These results are in agreement with

those obtained by Ghafouri and Lestienne (2006)

during a pointing task involving pointing to virtual

targets located in the sagittal, frontal and horizontal

planes. Errors were minimal for the sagittal and

frontal planes and maximal for horizontal plane.

These disparities in errors were considerably

reduced when subjects pointed using a visual guide.

These findings imply that different planes are

centrally represented, and are characterized, by

different errors when subjects use a body-centered

frame for performing the blind pointing and suggest

that the representation of peripersonal space may be

anisotropic. This study reveals the high stability of

the egocentric reference system (Lestienne and

Gurfinkel, 1988). This was consistent with the

finding of our previous works performed in

microgravity, dedicated to the perception and

interpretation of complex tactile stimuli (Gurfinkel

et al, 1993). Based on these findings we can assume

that tactile patterns encoding prescriptors are

perceived as a “local sign” taken into account in the

information about the configuration of the body

(Gurfinkel et al., 1994, and the appendix).

5 CONCLUSIONS

On the basis of the perceptual process of orientation

in 3D space through the use of tactile cues, the

results of this experiment establish the fact that

tactile information transmitted via our TC is

involved successfully in the processes of tactile

guidance of the hand in tridimensional space.

One of major advantages foreseen in using the

TC is its portability. This compact and lightweight

TC can be comfortably incorporated in the user’s

clothing without impairing movement.

On the basis of the positive experiences with the

TC, our laboratory has recently been involved in an

investigation into the potential of the TC in land

navigation.

The key to successful implementation of the TC

lies in the ability to convey effective directional

information that provided the user with a major

safety enhancement: “moving with hand and eye

free”.

In future work, the TC presents a number of

promising functional opportunities for use in clinical

and rehabilitation applications. These include

assistance in balancing and in coordinating

movements, combining the TC and virtual reality

techniques.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge Douglas

McCarthy for linguistic corrections and would like

to thank subject volunteers.

This research is founded by two projects:

-Ministère de l’Enseignement Supérieur et de la

Recherche (MESR): Action Concertées Incitative

(ACI 2004-2007) « Terrain, Techniques &

Théories » Langage tactile et orientation du corps

dans l’espace: une assistance technique au contrôle

de l’orientation dans l’espace tridimensionnel dans

le cas de déficits sensorimoteurs.

-Ministère de la Défense: Délégation Générale

pour l’Armement (DGA) Grant: REI (Exploratory

and Innovative Research) No 2008 34 0030.

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REFERENCES

Asseman, F., Brostein, A.M., Gresty, M.A., 2008,

Guidance of visual direction by topographical

vibrotacile cues on the torso, Exp Brain Res, 186,

283-292.

Bach-y-Rita, P., 1982, Sensory substitution, volume

transmission and rehabilitation: emerging concepts,

In Illis L-S (Ed), Neurological rehabilitation,

Blackwell, Oxford, 2nd edition, pp 457-468.

Bach-y-Rita, P., 2004, Tactile sensory substitution, Stud.

Ann.NY Acad. Sci., 1013, 83-91.

Bliss, J.C., Kather, M.N., Rogers, C.H., Shepard, R.P.,

1970, Optical-to-tactile image conversion for the

blind, IEEE Tans MMS, 11, 58-65.

Caffara, P., Mazzucchi, A., Parma, M., 1976, Osservazioni

sulla percezionne cutanea degli stimoli tattili figurati

nell uomo in condizioni normali, Boll Soc Ital Biol

Sperim. 52, 2092-2095.

Ghafouri, M., Lestienne, F.G., 2006, Contribution of

reference frames for movement planning in

peripersonal space representation, Exp Brain Res,

169, 24-36.

Gurfinkel, V.S., Lestienne, F., Levik, Yu S. Popov, K.E.,

1993, Egocentric references and human spatial

orientation in microgravity, I. Perception of complex

tactile stimuli. Exp Brain Res, 95(2), 339-342.

Jagacinski, R.J.,Miller, D.P., Gilson, R.D., 1979, A

comparison of kinesthetic-tactual and visual displays

in a critical tracking task, Human Factors, 21, 65-71.

Johansson, R.S., Landström U., Lundström R.J.I., 1982,

Responses of mechanoreceptive afferent units in the

glabrous skin of the human hand to sinusoidal skin

displacements, Brain Res., 244, 17-25.

Johnson, H.O., Phillips, J.R, 1981, Tactile spatial

resolution: I two-point discrimination, gap detection,

grating resolution and letter recognition, J

Neurophysiol, 46, 1177-1191.

Lestienne, F.G., Gurfinkel, V.S., 1988, Postural control in

weightlessness: a dual process underlying adaptation

to an unusual environment, Trends Neurosci 11: 359-

63.

Lepelley, M.C., 2008, Production du geste dans l’espace

tridimensionnel : du mouvement dansé au guidage

tactile du mouvement de pointage, PdD thesis,

Universty of Caen Basse-Normandie.

Lepelley M.C., El Idrissi H., Thullier F., Lestienne F.,

2005, Body orientation and identification of complex

tactile stimuli, Proceedings for 5

edition the Progress

in Motor Control, Pennsylvania State University.

Natsoulas, T., Dubanoski, R.A., 1964, Inferring the locus

and orientation of the perceiver from responses to

stimulation of the skin, Am J Psychol, 77, 281-285.

Parsons, L.M., Shimojo, S., 1987, Perceived spatial

orientation of cutaneous patterns on surfaces of the

human body in various positions, J Exp Psychol, 13,

488-504.

Phillips, J.R., 1988, Spatial pattern representation and

transformation in monkey somatosensory cortex,

Trends Neurosci, 11, 356-357.

Rochlis J.L., Newman D.J., 2000, A tactile display for

International Space Station (ISS) Extra Vehicular

Activity (EVA), Aviation, Space, and environmental

Medicine, 71, 571-578.

Van Erp J.B.F., 2005, Presenting directions with a

vibrotactile torso display, Ergonomics, 48 (3), 302–

313.

Van Erp J.B.F., Van Veen H.A.H.C., 2004, Vibrotactile

in-vehicle navigation system, Human Factors, 7, 247-

256.

Van Erp J.B.F., Werkhoven, P.W., 2004, Vibro-tactile and

visual asynchronies: Sensitivity and consistency,

Perception, 33, 103-111.

APPENDIX

Perception and interpretation of cutaneous stimuli

applied to the same tactile receptive field for

different posture and different orientation of the

body segment in question can yield valuable data

about the perceptual and gnostic functions during the

learning process in order to achieve tactile shape

recognition. The studies were conducted on 17

subjects. Two postures (see figure 9) were studied:

the vertical (1, 2) and horizontal positions (3, 4).

For each posture two conditions were examined:

with the right leg extended (1, 3) and during flexion

of the right leg at 90° between hip and knee joints

(2, 4).

In each situation, one of the 4 tactile stimuli was

presented: digits and simple geometric shapes (see

Figure 9). The TC was fixed on the frontal surface of

the right tight with Velcro strips. The results show

that the task of identification of complex tactile

stimuli was not affected by modification of posture

relative to the vertical gravitational body. However,

an increase in the frequency of errors was observed

when the leg was flexed: the part of the figure

closest the knee was perceived as being on top. It is

important to note that with more or less intensive

training, we observed a related improvement in the

task.

Information about the configuration of the body

part is taken into account during the stages of

processing the tactile signal.

Figure 9: Schematisation of the tactile stimuli (left) and

the postural conditions (right) (from Lepelley et al., 2005).

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