The performance of an artificial tongue-placed tactile biofeedback device for
improving ankle joint position sense was assessed in 12 young healthy adults
using an active matching task. The underlying principle of this system consists
of supplying individuals with supplementary information about the position of
the matching ankle relative to the reference ankle position through a
tongue-placed tactile output device generating electrotactile stimulation on a
36-point (6 X 6) matrix held against the surface of the tongue dorsum.
Precisely, (1) no electrodes were activated when both ankles were in a similar
angular position within a predetermined "angular dead zone" (ADZ); (2) 12
electrodes (2 X 6) of the anterior and posterior zones of the matrix were
activated (corresponding to the stimulation of the front and rear portion of
the tongue) when the matching ankle was in a too plantarflexed and dorsiflexed
position relative to the reference ankle, respectively. Two ADZ values of 0.5
degrees and 1.5 degrees were evaluated. Results showed (1) more accurate and
more consistent matching performances with than without biofeedback and (2)
more accurate and more consistent ankle joint matching performances when using
the biofeedback device with the smaller ADZ valu

Chenu, Olivier

Demongeot, Jacques

Fleury, Anthony

Payan, Yohan

Vuillerme, Nicolas

English

arXiv

N. Vuillerme

O. Chenu

A. Fleury

J. Demongeot

Y. Payan

Crossref

 
 
  
Abstract — The performance of an artificial tongue-placed 
tactile biofeedback device for improving ankle joint position 
sense was assessed in 12 young healthy adults using an active 
matching task. The underlying principle of this system 
consisted of supplying individuals with supplementary 
information about the position of the matching ankle relative to 
the reference ankle position through a tongue-placed tactile 
output device generating electrotactile stimulation on a 36-
point (6 × 6) matrix held against the surface of the tongue 
dorsum. Precisely, (1) no electrodes were activated when both 
ankles were in a similar angular position within a 
predetermined “angular dead zone” (ADZ); (2) 12 electrodes (2 
× 6) of the anterior and posterior zones of the matrix were 
activated (corresponding to the stimulation of the front and 
rear portion of the tongue) when the matching ankle was in a 
too plantarflexed and dorsiflexed position relative to the 
reference ankle, respectively. The effects of two ADZ values of 
0.5° and 1.5° were evaluated. Results showed (1) more accurate 
and more consistent matching performances with than without 
biofeedback and (2) more accurate and more consistent ankle 
joint matching performances when using the biofeedback 
device with the smaller ADZ value. These findings suggest that 
(1) electrotactile stimulation of the tongue can be used to 
improve ankle joint proprioception and (2) this improvement 
can be increased through an appropriate specification of the 
ADZ parameter provided by the biofeedback system. Further 
investigations are needed to strengthen the potential clinical 
value of this device. 
Keywords — Biofeedback; Tactile display; Tongue; Proprio-
ception; Human. 
 
I. INTRODUCTION 
N the last decades, a growing number of tactile displays 
have been developed for sensory substitution or 
augmentation systems (e.g., [1-4]). These devices are 
designed to evoke tactile sensation within the skin at the 
location of the tactile stimulator using either mechanical 
(“vibrotactile display”) or electrical (“electrotactile display”) 
stimulation. The skin being the interface between the tactile 
stimulator and the neural sensory system, the performance of 
a tactile display largely depends on the neurophysiologic 
characteristics of the receptive body regions. Along these 
lines, the human tongue has recently been suggested to 
 
Nicolas Vuillerme is with the TIMC-IMAG Laboratory, Equipe AFIRM, 
UMR CNRS 5525, Faculté de Médecine de Grenoble, Bâtiment Jean Roget, 
F38706 La Tronche Cédex; phone: +33 4 76 63 74 86; fax: +33 4 76 51 86 
67; mail: Nicolas.Vuillerme@imag.fr 
Olivier Chenu, Anthony Fleury, Jacques Demongeot and Yohan Payan 
are also with the TIMC-IMAG Laboratory, UMR CNRS 5525, La Tronche, 
France. Mail: firstname.lastname@imag.fr 
provide a promising electrotactile stimulation site [5]. 
Because of its dense mechanoreceptive innervations [6] and 
large somatosensory cortical representation [7], the tongue is 
indeed a very sensitive organ which can convey higher-
resolution information than the skin can [8-9]. In addition, 
due to the excellent conductivity offered by the saliva, 
electrotactile stimulation of the tongue requires only 3% of 
the voltage (5 - 15 V) and much less current (0.4 - 2.0 mA) 
than those required for the fingertip [5]. The Tongue Display 
Unit (TDU) has recently been developed to take advantage 
of these characteristics [5]. Initially used as a tactile-vision 
sensory substitution system to provide distal spatial 
information to blind people (e.g., [1,8,10,11]), the TDU also 
has proven its efficiency as a tactile-proprioception sensory 
augmentation system [12]. The performance of this system 
(“TDU-biofeedback system”) in improving proprioceptive 
acuity at the ankle joint recently has been evaluated on 
young healthy adults using an active matching task.  
 
 
Fig. 1. Photograph of the Tongue Display Unit used in the present 
experiment. It comprises a 2D electrode array (1.5 × 1.5 cm) consisting of 
36 gold-plated contacts each with a 1.4 mm diameter, arranged in a 6 × 6 
matrix. 
 
Position of the matching ankle relative to the reference 
ankle was fed back to a tongue-placed tactile output device 
generating electrotactile stimulation on a 36-point (6 × 6) 
matrix held against the surface of the tongue dorsum (Fig. 1) 
as follows: (1) no electrodes were activated when both 
ankles were in a similar angular position within a 
predetermined “angular dead zone” (ADZ); and (2) 12 
electrodes (2 × 6) of the anterior or posterior zones of the 
matrix were activated (corresponding to the stimulation of 
the front and rear portion of the tongue) when the matching 
ankle was in a too plantarflexed and dorsiflexed position 
relative to the reference ankle, respectively. Results of this 
experiment showed more accurate and more consistent 
matching performances when using the TDU-biofeedback 
system with an ADZ equal to 1,5°. At this point, it is 
Optimizing the Use of an Artificial Tongue-Placed Tactile 
Biofeedback for Improving Ankle Joint Position Sense in Humans 
N. Vuillerme, O. Chenu, A. Fleury, J. Demongeot and Y. Payan 
Laboratoire TIMC-IMAG, UMR CNRS 5525, La Tronche, France 
 
I 
 
 
possible that the observed effects markedly depend on the 
specification of the ADZ value. The purpose of the present 
study was thus designed to assess this possibility, by 
comparing the effects of providing two different ADZ values 
(0.5° and 1.5°) on the performance of the TDU-biofeedback 
system. It was hypothesized that (1) biofeedback delivered 
through the TDU would improve position sense at the ankle 
joint and (2) that this improvement would be larger with 
smaller ADZ value (0.5°). Note that such a result could 
provide further insight into the conception and optimization 
of rehabilitative programs or ergonomical assistive tools.  
II. METHODS 
A. Participants 
Twelve young healthy males adults (age = 27.7 ± 5.4 
years; body weight = 68.9 ± 6.9 kg; height = 177.7 ± 6.5 cm) 
volunteered for this study and gave their informed consent to 
the experimental procedure as required by the Helsinki 
declaration (1964) and the local Ethics Committee. None of 
the participants presented any history of injury, surgery or 
pathology to either lower extremity that could affect their 
ability to perform the experiment. 
 
Fig. 2. Illustration of the experimental setup used for measuring ankle joint 
position sense. 
 
B. Apparatus for measuring ankle joint position sense 
Participants were seated barefoot in a chair with their right 
and left foot secured to two rotating footplates. The knee 
joints were flexed at about 110°. Movement was restricted to 
the ankle in the sagittal plane, with no movement occurring 
at the hip or knee. The axes of rotation of the footplates were 
aligned with the axes of rotation of the ankles. Precision 
linear potentiometers attached on both footplates provided 
analog voltage signals proportional to the ankles’ angles. A 
handheld press-button allowed recording the matching. 
Signals from the potentiometers and the press-button were 
sampled at 100 Hz (12 bit A/D conversion), then processed 
and stored within the Labview 5.1 data acquisition system. 
In addition, a panel was placed above the subject’s legs to 
eliminate visual feedback about both ankles position (Fig. 
2). 
 
Fig. 3. Sensory coding schemes for the TDU (lower panels) as a function of 
the position of the matching right ankle relative to the reference left ankle 
(upper panels). Black dots represent activated electrodes. A: no electrodes 
are activated when both ankles are in a similar angular position within a 
range of 0.5° and 1.5°, for the TDU0.5° and TDU1.5° conditions, respectively. 
B: 12 electrodes (2 × 6) of the anterior zone of the matrix are activated 
(corresponding to the stimulation of the front portion of the tongue dorsum) 
when the matching right ankle was in a too plantarflexed position relative to 
the reference left ankle. C: 12 electrodes (2 × 6) of the posterior zone of the 
matrix are activated (corresponding to the stimulation of the rear portion of 
the tongue dorsum) when the matching right ankle was in a too dorsiflexed 
position relative to the reference left ankle. 
 
C. Apparatus for providing biofeedback: the TDU system  
The underlying principle of the biofeedback device used 
in the present experiment consisted of supplying participants 
with supplementary information about the position of the 
matching right ankle relative to the reference left ankle 
position through a tongue-placed tactile output device [12]. 
Electrotactile stimuli were delivered to the front part of the 
tongue dorsum via flexible electrode arrays placed in the 
mouth, with connection to the stimulator apparatus via a flat 
cable passing out of the mouth. The system comprises a 2D 
electrode array (1.5 × 1.5 cm) consisting of 36 gold-plated 
contacts each with a 1.4 mm diameter, arranged in a 6 × 6 
matrix [12] (Fig. 1).  
The following coding scheme for the TDU was used: (1) 
no electrical stimulation when both ankles were in a similar 
angular position within ADZs of 0.5° and 1.5°, for the 
TDU0.5° and TDU1.5° conditions, respectively (Fig. 3A); (2) 
stimulation of either the anterior or posterior zone of the 
matrix (2 × 6 matrix) (i.e. stimulation of front or rear 
portions of the tongue) depending on whether the matching 
right ankle was in a too plantarflexed or dorsiflexed position 
relative to the reference left ankle, respectively (Fig. 3B and 
3C, respectively). The frequency of the stimulation was 
maintained constant at 50 Hz across participants, ensuring a 
sensation of the continuous stimulation over the tongue 
surface. Conversely, the sensitivity to the electrotactile 
stimulation varying not only between individuals but also as 
a function of location on the tongue, as reported in a 
preliminary experiment [12], the intensity of the electrical 
stimulating current was adjusted for each subject, and for 
each of the front and rear portions of the tongue 
 
 
D. Task and procedure 
The experimenter first placed the left reference ankle at a 
predetermined angle where the position of the foot was 
maintained by means of a support [13]. By doing so, 
participants did not exert any effort to maintain the position 
of the left reference ankle, preventing the contribution of 
effort cues coming from the reference ankle to the sense of 
position during the test [13]. Two matching angular target 
positions were presented: (1) 10° of plantarflexion (P10°) and 
(2) 10° of dorsiflexion (D10°). These positions were selected 
to avoid the extremes of the ankle range of motion to 
minimize additional sensory input from joint and cutaneous 
receptors (e.g., [14]).  
Once the left foot had been positioned at the test angle 
(P10° vs. D10°), subject’s task was to match its position by 
voluntary placement of their right ankle. When they felt that 
they had reached the target angular position (i.e., when the 
right foot was presumably aligned with the left foot), they 
were asked to press the button held in their right hand, 
thereby registering the matched position.  
Three experimental conditions were presented: (1) the No-
TDU condition serving as a control condition, the (2) 
TDU0.5° and (3) TDU1.5° conditions in which participants 
performed the task using a TDU-biofeedback system, as 
described above (section IIC).  
Five trials for each target angular position and each 
experimental condition were performed. The order of 
presentation of the two targets angular positions (P10° vs. 
D10°) and the three experimental conditions (No-TDU vs. 
TDU0.5° vs. TDU1.5°) was randomized. Participants were not 
given feedback about their performance and errors in the 
position of the right ankle were not corrected.  
E. Data analysis 
Two dependent variables were used to assess matching 
performances [15]. (1) The absolute error (AE), the absolute 
value of the difference between the position of the right 
matching ankle and the position of the left reference ankle, is 
a measure of the overall accuracy of positioning. (2) The 
variable error (VE), the variance around the mean constant 
error score, is a measure of the variability of the positioning. 
Decreased AE and VE scores indicate increased accuracy 
and consistency of the positioning, respectively [15]. 
F.  Statistical analysis 
Data obtained for AE and VE were submitted to separate 
2 Targets angular positions (P10° vs. D10°) × 3 Conditions 
(No-TDU vs. TDU0.5° vs. TDU1.5°) analyses of variances 
(ANOVAs) with repeated measures of both factors. Post-hoc 
analyses (orthogonal planned comparisons) were performed 
whenever necessary. Level of significance was set at 0.05. 
 
 
Fig. 4. Mean and standard deviation for the absolute error (A) and the 
variable error (B) for the three No-TDU, TDU0.5° and TDU1.5° conditions. 
These three experimental conditions are presented with different symbols: 
No-TDU (white bars), TDU1.5° (black bars) and TDU0.5° (grey bars). (*: P < 
0.05, **: P < 0.01, ***: P < 0.001). 
 
III. RESULTS 
A. Positioning accuracy 
Analysis of the AE showed a main effect of Condition 
(F(2,22) = 39.76, P < 0.001, Fig. 4A), yielding smaller 
values in the TDU0.5° and TDU1.5° conditions than No-TDU 
condition (Ps < 0.001) and smaller values in the TDU0.5° 
than TDU1.5° condition (P < 0.05). The ANOVAs showed no 
main effect of Target angular position (P > 0.05), nor any 
interaction of Target angular position × Condition (P > 
0.05). 
 
B. Positioning variability 
Analysis of the VE showed a main effect of Condition 
(F(2,22) = 16.67, P < 0.001, Fig. 4B), yielding smaller 
values in the TDU0.5° and TDU1.5° conditions than No-TDU 
condition (P < 0.001 and P < 0.01, respectively) and smaller 
values in the TDU0.5° than TDU1.5° condition (P < 0.05). The 
ANOVAs showed no main effect of Target angular position 
(P > 0.05), nor any interaction of Target angular position × 
Condition (P > 0.05). 
 
IV. DISCUSSION AND CONCLUSION 
On the whole, more accurate and more consistent ankle 
joint matching performances were observed when the TDU 
biofeedback system was in use than when it was not. These 
results confirm our first hypothesis [12] and provide 
additional evidence that electrotactile stimulation of the 
tongue can be used to improve ankle joint proprioception. 
Interestingly, the performance of the TDU biofeedback 
system further was shown to depend on the specification of 
the ADZ parameter. Indeed, in accordance with our second 
hypothesis, more accurate and more consistent ankle joint 
matching performances were observed when using the TDU 
biofeedback system with the smaller ADZ value. An 
appropriate specification of this parameter could thus 
 
 
constitute a relevant means to increase the performance of 
the TDU biofeedback system. For instance, such a 
specification could allow optimizing the use of the tongue-
placed tactile biofeedback device as a rehabilitation protocol 
or assistance based tools, by taking the patient’s 
proprioceptive capabilities or the ongoing task’s accuracy 
requirement into account. Note that optimizing the TDU 
biofeedback system is all the more relevant since accurate 
proprioception at the ankle joint is critical for body 
orientation and balance control and represents a prerequisite 
for different functional activities such as walking, running or 
driving. At this point, further investigations involving 
individuals with proprioceptive deficits (e.g., elderly 
persons, patients with diabetic neuropathy) are needed to 
strengthen the potential clinical value of this technique. 
However, these encouraging results already have led us to 
improve the current TDU biofeedback system by making it 
wireless to increase its portability to permit its use over 
long-time period in real-life environment. Indeed, to be 
acceptable as part of a viable system, this device had to be 
lightweight, portable, and capable of several hours of 
continuous operations. The current ribbon TDU system does 
not meet these requirements yet. Within this context, we 
have developed a wireless radio-controlled version of the 6 × 
6 TDU matrix. This consists in a matrix glued onto the 
inferior part of the orthodontic retainer including 
microelectronics, antenna and battery, which can be worn 
inside the mouth like a dental retainer. This wearable device 
is currently tested by our industrial partner (Coronis-Systems 
www.coronis-systems.com) that will provide Wavenis, its 
wireless Ultra Lower Power technology which has been 
preferred to current radio frequency (RF) standards that have 
shortcomings when considering Ultra Low Power 
challenges.  
ACKNOWLEDGMENT 
We are indebted to Professor Paul Bach-y-Rita for 
introducing us to the TDU and for discussions about sensory 
substitution. The authors would like to thank subject 
volunteers. Special thanks also are extended to D. 
Flammarion and S. Maubleu for technical assistance and P. 
Ipou and L. Egland for various contributions. 
REFERENCES 
[1] P. Bach-y-Rita, “Tactile sensory substitution studies,” Ann. N.Y. 
Acad. Sci., vol. 1013, pp. 83-91, 2004.  
[2] K.A. Kaczmareck, J.G. Webster, P. Bach-y-Rita, and W.J. Tompkins, 
“Electrotactile and vibrotactile displays for sensory substitution 
systems,” IEEE Trans. Rehabil. Eng., vol. 38, pp. 1-16, 1991. 
[3] J.W. Shim, W. Liu, and H. Tang, “System development for 
multichannel electrotactile stimulation on the lips,” Med. Eng. Phys., 
2006, in press. 
[4] M. Shinohara, Y. Shimizu, and A. Mochizuki, “Three-dimensional 
tactile display for the blind,” IEEE Trans. Rehabil. Eng., vol. 6, pp. 
249-256, 1998. 
[5] P. Bach-y-Rita, K.A. Kaczmarek, M.E. Tyler, and J. Garcia-Lara, 
“Form perception with a 49-point electrotactile stimulus array on the 
tongue,” J. Rehabil. Res. Dev., vol. 35, pp. 427-430, 1998. 
[6] M. Trulsson, and G.K. Essick, “Low-threshold mechanoreceptive 
afferents in the human lingual nerve,” J. Neurophysiol., vol. 77, pp. 
737-748, 1997. 
[7] C. Picard, and A. Olivier, “Sensory cortical tongue representation in 
man,” J. Neurosurg., vol. 59, pp. 781-789, 1983. 
[8] E. Sampaio, S. Maris, and P. Bach-y-Rita, “Brain plasticity: ‘visual’ 
acuity of blind persons via the tongue,” Brain Res., vol. 908, pp. 204-
207, 2001. 
[9] R.W. van Boven, and K.O. Johnson, “The limit of tactile spatial 
resolution in humans: grating orientation discrimination at the lips, 
tongue, and finger,” Neurology, vol. 44, pp. 2361-2366, 1994.  
[10] P. Bach-y-Rita, M.E. Tyler, and K.A. Kaczmarek, “Seeing with the 
brain,” Int. J. Hum-Comput. Int., vol. 15, pp. 285-295, 2003. 
[11] P. Bach-y-Rita1, and SW. Kercel, “Sensory substitution and the 
human-machine interface,” Trends Cogn. Sci., vol. 7, pp. 541-546, 
2003. 
[12] N. Vuillerme, O. Chenu, J. Demongeot, and Y. Payan, “Improving 
human ankle joint position sense using an artificial tongue-placed 
tactile biofeedback,” Neurosci. Lett., 2006, in press. 
[13] L.D. Walsh, C.W. Hesse, D.L. Morgan, and U. Proske, “Human 
forearm position sense after fatigue elbow flexor muscle,” J. Physiol., 
vol. 558, pp. 705-715, 2004. 
[14] D. Burke, S.C. Gandevia, and G. Macefield, “Responses to passive 
movement of receptors in joint, skin and muscle of the human hand,” 
J. Physiol., vol. 402, pp. 347-361, 1988. 
[15] R.A. Schmidt, Motor Control and Learning, 2nd Edition. Human 
Kinetics, Champaign, IL, 1988.  
 


Optimizing the Use of an Artificial Tongue-Placed Tactile Biofeedback for Improving Ankle Joint Position Sense in Humans

International audienceThe performance of an artificial tongue-placed tactile biofeedback device for improving ankle joint position sense was assessed in 12 young healthy adults using an active matching task. The underlying principle of this system consists of supplying individuals with supplementary information about the position of the matching ankle relative to the reference ankle position through a tongue-placed tactile output device generating electrotactile stimulation on a 36-point (6 X 6) matrix held against the surface of the tongue dorsum. Precisely, (1) no electrodes were activated when both ankles were in a similar angular position within a predetermined “angular dead zone” (ADZ); (2) 12 electrodes (2 X 6) of the anterior and posterior zones of the matrix were activated (corresponding to the stimulation of the front and rear portion of the tongue) when the matching ankle was in a too plantarflexed and dorsiflexed position relative to the reference ankle, respectively. Two ADZ values of 0.5° and 1.5° were evaluated. Results showed (1) more accurate and more consistent matching performances with than without biofeedback and (2) more accurate and more consistent ankle joint matching performances when using the biofeedback device with the smaller ADZ valu

Hal - Université Grenoble Alpes

HAL Descartes

https://hal.archives-ouvertes.fr/hal-00108512

Optimizing the Use of an Artificial Tongue-Placed Tactile Biofeedback
  for Improving Ankle Joint Position Sense in Humans

Optimizing the Use of an Artificial Tongue-Placed Tactile Biofeedback for Improving Ankle Joint Position Sense in Humans

Abstract

Similar works

Full text

Available Versions

Crossref

Hal - Université Grenoble Alpes

Crossref

Crossref

Crossref

HAL Descartes