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Journal ArticleDOI

The Variability of Psychophysical Parameters Following Surface and Subdermal Stimulation: A Multiday Study in Amputees

01 Jan 2020-Vol. 28, Iss: 1, pp 174-180

TL;DR: The outcome of this study has implications for the choice of modality in delivering sensory feedback, though the significance of the quantified variability needs to be evaluated using usability tests with user feedback.

AbstractElectrotactile stimulation has been suggested as a modality for providing sensory feedback in upper limb prostheses. This study investigates the multiday variability of subdermal and surface stimulation. Electrical stimulation was delivered using either surface or fine wire electrodes placed right under the skin in eight amputees for seven consecutive days. The variability of psychophysical measurements, including detection threshold (DT), pain threshold (PT), dynamic range (DR), just noticeable difference (JND), Weber fraction (WF) and quality of evoked sensations, was evaluated using the coefficient of variation (CoV). In addition, the systematic change in the mean of the parameters across days was assessed in both stimulation modalities. In the case of DT, PT, DR, and perceived intensity at 100 Hz, the CoV of surface stimulation was significantly smaller than that of subdermal stimulation. Only PT showed a significant systematic change in the mean value across days for both modalities. The outcome of this study has implications for the choice of modality in delivering sensory feedback, though the significance of the quantified variability needs to be evaluated using usability tests with user feedback.

Summary (3 min read)

I. INTRODUCTION

  • Round 1.6 million people were living with limb amputation in the year 2005, and it has been estimated that 3.6 million people will be living with amputation in the United States of America by the year 2050 [1] .
  • For upper limb prosthetic users, the absence of sensory feedback impedes the efficient use of their prostheses, which can lead to user frustration and abandonment of the device [2] .
  • The feedback can be restored through invasive methods as well, i.e. by electrically stimulating peripheral nerves [10] .
  • The information about grasping force, slippage [12] , hand aperture [13] , finger flexion [14] , and elbow angle has been previously encoded and transmitted through sensory feedback [7] , [15] .
  • Subdermal stimulation can lead to substantially more compact feedback interfaces, since it is based on point electrodes (wire tip), and it can substantially decrease the required voltage and current consumption because skin impedance is bypassed.

A. Subjects

  • Subjects provided written informed consent and the study adhered to the Helsinki Declaration.
  • All subjects had undergone traumatic amputation of their dominant hand/arm.
  • None of the subjects abused cannabis, opioids or other drugs.
  • One subject was excluded from the study because a pain threshold could not be reached even with a current amplitude of 40 mA (the highest possible current to deliver) and at that high stimulation level, strong muscle twitches were evoked.

B. Experiment procedure

  • A single session was performed each day for seven consecutive days.
  • The psychophysical measurements were collected in the order of DT, PT, JND and sensation evaluation in each session.
  • All seven sessions were scheduled at the same time of the day.
  • The surface electrodes were disposed following each session.
  • This protocol was selected to mimic the real-life application in which the surface electrodes are reapplied with each donning and doffing, while the subdermal electrodes will be placed permanently.

C. Stimulation

  • A programmable stimulator (ISIS Neurostimulator, Inomed, Germany) was used to generate biphasic, rectangular, symmetric pulses with a pulse width of 200 μs.
  • The stimulator was controlled by a custom-made program implemented in LabVIEW version 2015 running on a laptop.
  • The subdermal wire electrodes were made of Teflon-coated stainless steel (A-M Systems, Carlsborg WA, diameter 50 µm), with 5-mm tip exposed [21] .
  • Each subject was checked to see if the stump of his forearm had enough normal skin (the skin without any visible scar and any abnormal sensation) for electrode placement.
  • The surface electrode was placed just next to the wire (Fig. 1 ).

D. Psychophysical measurements 1) Detection threshold and pain threshold

  • The smallest stimulus that can be detected by the subject is called DT.
  • This amplitude was then used as the initial amplitude in the staircase procedure.
  • During the staircase testing, a series of stimuli were delivered to the subjects with the amplitude that was adjusted adaptively based on subject responses.
  • If the subject detected the stimulus, the amplitude was increased, otherwise decreased (in steps of 0.03-0.05 mA for surface and 0.01-0.03 mA for subdermal stimulation).
  • The DT was computed as the average of the last seven reversals.

) Just noticeable difference

  • The smallest change in the stimulus amplitude that can be detected by a subject is called the JND.
  • The pairs of pulses were delivered until the subject reported that he could feel the difference in the intensity.
  • According to Weber's law, the WF should be approximately constant, and therefore, it can be used to estimate the JND for different baselines.
  • To describe the location of the perception, the subjects could select one of the three options, namely, 'local', 'radiation' and 'referred'.
  • Finally, the selection ratios (average scores of the 3 stimulation sequences) were used for data analysis for the sensation quality and sensation location of each item.

E. Data analysis

  • The coefficient of variation (CoV) was computed to evaluate the variability of DT, PT, WF, DR, intensity, and comfort across seven days.
  • Then, the parametric paired sample ttest was used to compare CoVs between the surface and subdermal stimulation if the data were normally distributed, otherwise, the non-parametric Wilcoxon signed-rank test was used.
  • The CoV values were expressed in percent.
  • In both cases, post hoc pairwise tests (Tukey's HSD criterion) were performed if a significant difference was detected across days.
  • Statistics were performed using IBM SPSS version 25 except the Skilling-Mack test, which was performed using Statext v3.0.

A. PT, DT, and DR

  • There was a significant difference (p ˂ 0.05) between the surface and subdermal stimulation in the CoVs of both DT and PT.
  • Therefore, both DT and PT were more variable in the case of subdermal stimulation.
  • There was a significant difference (p ˂ 0.05) between the surface and subdermal stimulation in the CoVs of the DR.
  • Therefore, DR was more variable across seven days in subdermal stimulation.

B. WF (JND)

  • There was no significant difference between the surface (64.66 ± 45.52 %) and subdermal stimulation (37.90 ± 7.13 %), likely due to high variability of the CoVs across subjects in surface stimulation.
  • There was no significant change in the mean WF of both surface and subdermal stimulation across the seven days, which means that both surface and subdermal stimulation were stable across days (no systematic trends).

C. Evoked sensation 1) Quality of sensation and perceived location

  • The sensation quality and perceived location for surface and subdermal stimulation exhibited a similar degree of variability across the seven days (p > 0.05 for all).
  • As shown in Fig. 6 , the selection ratios of pressure, vibration, tingling and movement for surface stimulation seem to be higher than for subdermal stimulation, while there is an opposite trend for the selection ratios of pinprick and warm sensations.

IV. DISCUSSION

  • Two aspects of the psychophysical measurements were explored, one is variability (CoV) and the other is the stability of the mean (systematic trend).
  • Therefore, the environment in the tissue around the electrode might have changed, thereby influencing the psychophysical measurements.
  • In fact, there was no re-insertion of the subdermal electrode during the seven days, as the re-insertion would be an additional source of variability.
  • It provides chronic placement with a simple procedure (needle insertion).
  • As demonstrated here, both subdermal and surface stimulation are stable (no systematic change) but the psychometric parameters of the subdermal stimulation exhibit more intrinsic variability.

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DOI:
10.1109/TNSRE.2019.2956836
Document Version
Peer reviewed version
Link to publication record in King's Research Portal
Citation for published version (APA):
Dong, J., Geng, B., Khan Niazi, I., Amjad, I., Dosen, S., Jensen, W., & Kamavuako, E. N. (2020). The Variability
of Psychophysical Parameters following Surface and Subdermal Stimulation: A Multiday Study in Amputees.
IEEE transactions on neural systems and rehabilitation engineering , 28(1), 174-180. [8918067].
https://doi.org/10.1109/TNSRE.2019.2956836
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Download date: 09. Aug. 2022

> TNSRE-2019-00349 <
1
Abstract—Electrotactile stimulation has been suggested as a
modality for providing sensory feedback in upper limb prostheses.
This study investigates the multiday variability of subdermal and
surface stimulation. Electrical stimulation was delivered using
either surface or fine wire electrodes placed right under the skin
in eight amputees for seven consecutive days. The variability of
psychophysical measurements, including detection threshold
(DT), pain threshold (PT), dynamic range (DR), just noticeable
difference (JND), Weber fraction (WF) and quality of evoked
sensations, was evaluated using the coefficient of variation (CoV).
In addition, the systematic change in the mean of the parameters
across days was assessed in both stimulation modalities. In the case
of DT, PT, DR, and perceived intensity at 100 Hz, the CoV of
surface stimulation was significantly smaller than that of
subdermal stimulation. Only PT showed a significant systematic
change in the mean value across days for both modalities. The
outcome of this study has implications for the choice of modality
in delivering sensory feedback, though the significance of the
quantified variability needs to be evaluated using usability tests
with user feedback.
Index Terms—Prostheses, surface electrotactile stimulation,
subdermal electrical stimulation, sensory feedback, sensation
variability.
I. INTRODUCTION
round 1.6 million people were living with limb amputation
in the year 2005, and it has been estimated that 3.6 million
people will be living with amputation in the United States of
America by the year 2050 [1]. Currently, some of the
functionality of a lost arm can be replaced by a prosthesis. A
prosthesis is defined as an artificial device that replaces a
biological limb both functionally and morphologically. The
human hand has a highly complex structure that comprises
many degrees of freedom; the hand has remarkable capabilities
in performing dexterous and delicate movements. This is
possible due to the sophisticated closed-loop control integrating
This work was supported by the Danish Ministry of Higher Education and
Science The Danish Council for Independent Research | Technology and
Production Sciences under Grant 1337-00130.
Jian Dong is with the Department of Orthopedics, The Second Hospital of
Jilin University, Changchun 130041, China. He is now with SMI®, the
Department of Health Science and Technology, Aalborg University, 9220
Aalborg, Denmark (e-mail: jd@hst.aau.dk).
Bo Geng, Strahinja Dosen and Winnie Jensen are with SMI®, the
Department of Health Science and Technology, Aalborg University, 9220
Aalborg, Denmark.
efferent motor output and afferent sensory feedback.
Consequently, mimicking the structure and function of the
human hand using an artificial system is a very challenging
task.
Even though advanced prosthetic hands that can partly
replicate the motor dexterity of a natural human hand are
available (e.g. DEKA Hand and iLimb), a continuing challenge
is to restore the sensory function of the hand. For upper limb
prosthetic users, the absence of sensory feedback impedes the
efficient use of their prostheses, which can lead to user
frustration and abandonment of the device [2]. The sensory
awareness, which is available with body-powered prostheses
due to a direct connection between the gripper and the user's
shoulder, does not exist in myo-electrically controlled systems
[3]. In this case, the users must rely primarily on the direct
observation of the device (visual feedback) [4] and secondarily,
on subtle clues such as the sounds of the motor and transmission
(intrinsic feedback) [5]. Therefore, restoring somatosensory
feedback to the prosthesis user can decrease visual attention and
improve control by providing explicit information about the
state of the device.
The somatosensory feedback can be provided using different
stimulation methods to elicit tactile sensations [6]. Current non-
invasive solutions are mostly based on delivering
electrocutaneous stimulation [7], or vibration [8] to the skin on
the residual limb. The residual limb can also be stimulated
mechanically (e.g. pushing the limb by using a force applicator,
squeezing the limb by a cuff, or by stretching the skin) [9]. The
feedback can be restored through invasive methods as well, i.e.
by electrically stimulating peripheral nerves [10]. In this case,
the aim of the stimulation is to activate the same neural
structures that have been used before the amputation, leading to
somatotopic feedback. The same result may be achieved using
non-invasive methods by delivering the stimulus to the
Imran Khan Niazi is with New Zealand College of Chiropractic, 1060
Auckland, New Zealand; SMI®, Department of Health Science and
Technology, 9220 Aalborg University, Denmark; Health and Rehabilitation
Research Institute, AUT University, 1142 Auckland, New Zealand.
Imran Amjad is with Riphah College of Rehabilitation Sciences, Riphah
International University, H-8/2 Islamabad, Pakistan.
Ernest Nlandu Kamavuako is with the Centre for Robotics Research,
Department of Informatics, King’s College London, WC2B 4BG London,
United Kingdom.
The Variability of Psychophysical Parameters
following Surface and Subdermal Stimulation:
A Multiday Study in Amputees
Jian Dong, Bo Geng, Imran Khan Niazi, Imran Amjad, Strahinja Dosen, IEEE Member, Winnie
Jensen and Ernest Nlandu Kamavuako, IEEE Member
A

> TNSRE-2019-00349 <
2
phantom map if it exists on the residual limb [11].
In general, the feedback information is transmitted by
relating a measured prosthesis variable to selected stimulation
parameters. For example, the magnitude of the grasping force
can be communicated using the magnitude or frequency of
stimulation. Therefore, the user needs to learn to relate the
stimulation parameters to the prosthesis state, and this requires
training. The information about grasping force, slippage [12],
hand aperture [13], finger flexion [14], and elbow angle has
been previously encoded and transmitted through sensory
feedback [7], [15].
The electrocutaneous stimulation is an attractive modality to
restore feedback and it has been investigated intensively in the
past [16]. The stimulation can be delivered using simple and
compact circuits and electrodes [17]. Therefore, the
electrotactile interface is convenient for providing multichannel
feedback and integration into a prosthetic socket. Furthermore,
since there are no moving mechanical parts, the stimulation
parameters can be changed fast and independently. This allows
eliciting rich and dynamic tactile sensations. Studies with able-
bodied subjects and amputees have shown that electrotactile
feedback can improve prosthesis control [18], [19].
Nevertheless, a disadvantage of electrocutaneous stimulation
delivered through surface electrodes is that it can produce
uncomfortable and even painful sensations. High voltage is
needed for the stimulation to overcome the skin impedance,
which can also vary depending on the conditions of the
electrode-skin interface. To increase the dynamic range,
between the sensation and pain threshold, larger electrodes are
required. Importantly, these drawbacks may be overcome by
placing the electrodes subdermally, as previously demonstrated
[20], [21]. Subdermal stimulation can lead to substantially more
compact feedback interfaces, since it is based on point
electrodes (wire tip), and it can substantially decrease the
required voltage and current consumption because skin
impedance is bypassed. As a step in this direction,
psychophysical measurements were conducted previously [21]
to evaluate and compare the properties of the surface and
subdermal stimulation.
Ideally, a feedback interface needs to produce stable and
repeatable sensations. This is even more important when using
subdermal stimulation since the electrodes are meant to stay
within the tissue for its lifetime, contrary to surface stimulation
where they will be reapplied with each donning and doffing of
the prosthesis. The short-term stability of subdermal
stimulation has been tested in our previous study for up to eight
hours [22]. However, long-term stability plays an important
role in achieving the long-lasting functional sensory feedback
and verifying its usability in clinical applications for amputees
[23], [24]. In general, the multiday variability of the commonly
used psychophysical measurements has received less attention
in the literature.
Therefore, the aim of this study was to investigate the
variability of psychophysical measurements over the course of
seven days when using subdermal versus surface stimulation in
upper-limb amputees. The psychophysical measurements that
were investigated systematically in the present study were
detection threshold (DT), pain threshold (PT), dynamic range
(DR), just noticeable difference (JND), Weber fraction (WF)
and the subjective quality of evoked sensations.
II. METHODS
A. Subjects
Nine male upper-limb amputees (33.6 ± 12.9 years old, 13.7
± 11.1 years after amputation) were recruited from Railway
General Hospital, Rawalpindi, Pakistan (Table I). Subjects
provided written informed consent and the study adhered to the
Helsinki Declaration. The ethical committee of Riphah
International University (N-ref# Riphah/
RCRS/REC/000121/20012016) approved the study protocol.
All subjects had undergone traumatic amputation of their
dominant hand/arm. None of the subjects abused cannabis,
opioids or other drugs. They had no record of previous
neurological, musculoskeletal or mental illnesses, lack of
ability to cooperate, fear of injections; and they were all
phantom pain-free. One subject was excluded from the study
because a pain threshold could not be reached even with a
current amplitude of 40 mA (the highest possible current to
deliver) and at that high stimulation level, strong muscle
twitches were evoked.
B. Experiment procedure
A single session was performed each day for seven
consecutive days. The psychophysical measurements were
collected in the order of DT, PT, JND and sensation evaluation
in each session. All seven sessions were scheduled at the same
time of the day. The subdermal electrode was disconnected
after each session and it remained under the skin for the
duration of the experiment. The insertion site and the wire were
wrapped with a medical bandage between different sessions, to
minimize displacement of the electrode during daily activities.
The surface electrodes were disposed following each session.
This protocol was selected to mimic the real-life application in
which the surface electrodes are reapplied with each donning
and doffing, while the subdermal electrodes will be placed
permanently. The common ground electrode was also removed
at the end of the session. The same common ground electrode
was reused for three or four sessions depending on the
stickiness and conductivity.
TABLE I
D
EMOGRAPHIC
D
ATA
OF
THE
S
UBJECTS
Subject
Age
Years after
amputation
Amputation level
Cause of
amputation
1
59
31
Transradial
Trauma
2
29
15
Transradial
Trauma
3
19
14
Wrist disarticulation
Trauma
4
30
3
Partial hand
Trauma
5
52
2
Partial hand
Trauma
6
36
31
Wrist disarticulation
Trauma
7
32
7
Wrist disarticulation
Trauma
8
19
14
Partial hand
Trauma
9
26
14
Partial hand
Trauma
All subjects were undergoing dominant side amputation.

> TNSRE-2019-00349 <
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C. Stimulation
A programmable stimulator (ISIS Neurostimulator, Inomed,
Germany) was used to generate biphasic, rectangular,
symmetric pulses with a pulse width of 200 μs. The stimulator
was controlled by a custom-made program implemented in
LabVIEW version 2015 running on a laptop.
Commercially available surface electrodes (Ambu Neuroline
700, 20 mm 15 mm) and subdermal fine wire electrodes were
used to deliver the electrical stimulation. The subdermal wire
electrodes were made of Teflon-coated stainless steel (A-M
Systems, Carlsborg WA, diameter 50 µm), with 5-mm tip
exposed [21]. Each subject was checked to see if the stump of
his forearm had enough normal skin (the skin without any
visible scar and any abnormal sensation) for electrode
placement. The two stimulation electrodes were positioned on
the dorsal side of the proximal end of the stump. The subject
was seated on a chair with their stump exposed, and the skin of
the dorsal stump was shaved in the area of approximately 2 cm
3 cm. The skin location was cleaned with a 70% alcohol swab
and the wire was inserted subdermally using a 25-gauge
hypodermic needle. The rest of the wire electrode was fixed to
the skin by Fixomull® stretch tape to avoid any displacement.
The surface electrode was placed just next to the wire (Fig. 1).
The pre-gelled common ground electrode (PALS Platinum, 40
mm 64 mm, oval) was applied to the dorsal side of the upper
arm next to the elbow.
D. Psychophysical measurements
1) Detection threshold and pain threshold
The smallest stimulus that can be detected by the subject is
called DT. The DT was measured using a staircase method by
delivering single pulses with an inter-pulse interval of 2 s [25].
To initialize the staircase, an approximate DT was first
determined using the method of limits [26]. The subjects
received a series of pulses gradually increasing in steps of 0.3-
0.5 mA for surface and 0.1-0.3 mA for subdermal stimulation.
The steps were chosen randomly within the indicated range to
avoid any anticipation bias by the subjects [22]. The amputee
reported verbally when he first felt the stimulation. This
amplitude was then used as the initial amplitude in the staircase
procedure. During the staircase testing, a series of stimuli were
delivered to the subjects with the amplitude that was adjusted
adaptively based on subject responses. After each pulse, the
subject reported if he felt the stimulation. If the subject detected
the stimulus, the amplitude was increased, otherwise decreased
(in steps of 0.03-0.05 mA for surface and 0.01-0.03 mA for
subdermal stimulation). The amplitude changes from ‘increase’
to ‘decrease’ or vice versa was defined as a ‘reversal’. The
staircase procedure stopped after 10 reversals or after 30 stimuli
were delivered. The DT was computed as the average of the last
seven reversals.
The stimulus amplitude at which the subject starts to feel pain
is referred to as the PT. The PT was measured using the method
of limits [26] by delivering a single pulse with increasing
amplitude in steps of 0.3-0.5 mA for surface and 0.1-0.3 mA for
subdermal stimulation [22] and with an inter-pulse interval of 2
s. Three measurements were performed, and the PT was
determined as the average of those measurements.
The DR was calculated by dividing PT by DT. A larger DR
indicates that a wider range of electrical stimulation amplitudes
is tolerated by the subject and may also generate a wider range
of sensations (more room to operate).
2) Just noticeable difference
The smallest change in the stimulus amplitude that can be
detected by a subject is called the JND. The JND was
determined using the method of limits [26]. The amplitude of
the baseline stimulus was set at 3×DT in both surface and
subdermal stimulation. If this intensity was higher than the PT,
a lower amplitude of 2×DT or DT was used. Two stimuli
were delivered sequentially and there was a 2-s break between
the pulses. The first pulse was always set to the baseline
amplitude whereas the amplitude of the second pulse was
increased in steps of 0.01-0.11 mA for surface and 0.02-0.07
mA for subdermal. The pairs of pulses were delivered until the
subject reported that he could feel the difference in the intensity.
The difference was recorded as the JND. Finally, the procedure
was repeated three times and the average of the three JNDs was
used for data analysis.
The ratio between the JND and the baseline amplitude is
called WF [18]. The WF was calculated using equation as
follows:
𝑊𝐹 = ΔI/Δ
where ΔI is JND and Δ is the baseline amplitude. According to
Weber’s law, the WF should be approximately constant, and
therefore, it can be used to estimate the JND for different
baselines. Hence, the WF characterizes the resolution of the
perceptual system.
3) Sensation evaluation
A computerized questionnaire was designed (Fig. 2) to
collect the subjective experience of the stimulation [13]. The
subjects were asked to report on the sensation quality, intensity,
comfort, and location. The questionnaire included 12 pre-
defined words that could be selected by the subject to describe
the quality. For the stimulus intensity, the subjects were asked
to indicate a number from a numerical rating scale (NRS),
where 0 represented no stimulation and 10 represented the
Fig. 1. Diagram of electrodes placement.

> TNSRE-2019-00349 <
4
maximum intensity. The stimulus comfort was reported using a
Likert-type scale, where one indicated very comfortable, four
neutral and seven very uncomfortable sensations. To describe
the location of the perception, the subjects could select one of
the three options, namely, 'local', 'radiation' and 'referred'.
'Local' represents that the sensation was just beneath the
electrodes. 'Radiation' indicates that the sensation radiated out
from the electrodes. 'Referred' represents that the sensation
appeared at the other part of the body. All the answers were
recorded on a computer via LabVIEW. The NRS and Likert
scale were implemented using sliders and therefore the subject
could indicate any number within the allowed range.
To evaluate the sensation quality, intensity, comfort, and
location (questionnaire contents), the stimulation was delivered
to the subjects in the form of 1-s pulse trains. The amplitude of
the pulse trains was set to 3×DT and the frequency at 20 Hz and
100 Hz. These frequencies were selected as a) they elicit
different sensations, 20 Hz elicits vibration and 100 Hz fused
tingling, and b) they are within the range typically used for
sensory feedback [27]. The amplitude of 1× DT or 2×DT was
used if 3×DT was over PT. Each frequency was delivered to the
subjects three times, and after each delivery, the subject was
asked to fill in the aforementioned questionnaire. The stimuli at
50 Hz and 80 Hz were used as oddballs and delivered 2 times
each. Twenty pulse trains (10 surface stimuli and 10 subdermal
stimuli) were delivered to the subjects and the order of
application of different frequencies was randomized. With
sensation quality and location, the score was recorded as 1 if the
specific word was selected; otherwise, the score was recorded
as 0. Finally, the selection ratios (average scores of the 3
stimulation sequences) were used for data analysis for the
sensation quality and sensation location of each item. With
intensity and comfort, the average value of the three stimulation
sequences was used for data analysis.
E. Data analysis
The coefficient of variation (CoV) was computed to evaluate
the variability of DT, PT, WF, DR, intensity, and comfort
across seven days. CoV was calculated as follows:
𝐶𝑜𝑉 =
(
𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝐷𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛/𝑀𝑒𝑎𝑛
)
× 100
Finally, 8 CoVs (8 subjects) were obtained as a measure of
within-subject variability across seven days for surface and
subdermal stimulation. Then, the parametric paired sample t-
test was used to compare CoVs between the surface and
subdermal stimulation if the data were normally distributed,
otherwise, the non-parametric Wilcoxon signed-rank test was
used. The CoV values were expressed in percent.
One-way repeated-measures ANOVA was applied to detect
if the psychometric parameters (DT, PT, DR, WF) changed
significantly across the seven days when the data were normally
distributed (Shapiro-Wilk test), otherwise, the Friedman test
was used. In both cases, post hoc pairwise tests (Tukey’s HSD
criterion) were performed if a significant difference was
detected across days.
Skilling-Mack test was used for difference detection across
the seven days in sensation quality, intensity, comfort, and
location data since this test can be used in any block design and
in the presence of missing data. Results are reported as mean ±
standard deviation (M ± SD). Statistics were performed using
IBM SPSS version 25 except the Skilling-Mack test, which was
performed using Statext v3.0. The statistical significance
threshold was set at p < 0.05.
III. RESULTS
A. PT, DT, and DR
The average CoVs of the DT and PT for surface and
subdermal stimulation are shown in Fig. 3. There was a
significant difference (p ˂ 0.05) between the surface and
subdermal stimulation in the CoVs of both DT and PT. The
CoVs for DT were 13.41 ± 5.11 % vs 22.30 ± 5.06 % and for
PT were 16.25 ± 6.93 % vs 20.00 ± 3.60 % in surface and
subdermal stimulation, respectively. Therefore, both DT and
PT were more variable in the case of subdermal stimulation.
There was no significant difference across seven days in the
mean DT of both surface and subdermal stimulation (Fig. 4 A
and B). However, the PT in surface and subdermal stimulation
increased across the seven-day period as shown in Fig. 4 C and
D. The regression fit lines were significantly different from zero
(p ˂ 0.05). The mean PT of surface stimulation changed
significantly across seven days, as detected by the Friedman test.
The post hoc tests revealed that the PT of the second (19.76 mA
± 4.59 mA) and third day (20.60 mA ± 4.43 mA) was
Fig. 3. The average (mean ± standard deviation) coefficient of variation (CoV
)
for detection threshold (DT) and pain threshold (PT)
across seven days for
subdermal (gray) and surface (black) stimulation. ⁎ p ˂ 0.05.
Fig. 2. Questionnaire for sensation evaluation.

Citations
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13 Aug 2020
TL;DR: A flexible, transversal intraneural tungsten:titanium electrode array for acute studies is introduced and it is shown that the stimulation of peripheral nerves with this electrode array is possible and that more than half of the electrode contacts can yield a stimulation selectivity index of 0.75 or higher at low stimulation currents.
Abstract: The development of hardware for neural interfacing remains a technical challenge. We introduce a flexible, transversal intraneural tungsten:titanium electrode array for acute studies. We characterize the electrochemical properties of this new combination of tungsten and titanium using cyclic voltammetry and electrochemical impedance spectroscopy. With an in-vivo rodent study, we show that the stimulation of peripheral nerves with this electrode array is possible and that more than half of the electrode contacts can yield a stimulation selectivity index of 0.75 or higher at low stimulation currents. This feasibility study paves the way for the development of future cost-effective and easy-to-fabricate neural interfacing electrodes for acute settings, which ultimately can inform the development of technologies that enable bi-directional communication with the human nervous system.

2 citations


Cites background from "The Variability of Psychophysical P..."

  • ...DELIVERING sensory feedback for prosthesis users has attracted a significant level of scientific and clinical interest [1]–[5]....

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Posted ContentDOI
TL;DR: Electrotactile feedback was successful in rendering and/or augmenting most tactile sensations, eliciting perceptual processes, and improving performance in many scenarios, especially in those where the wearability/portability of the system is important.
Abstract: Haptic feedback is critical in a broad range of human-machine/computer-interaction applications. However, the high cost and low portability/wearability of haptic devices remains an unresolved issue, severely limiting the adoption of this otherwise promising technology. Electrotactile interfaces have the advantage of being more portable and wearable due to its reduced actuators’ size, as well as benefiting from lower power consumption and manufacturing cost. The usages of electrotactile feedback have been explored in human-computer interaction and human machine-interaction for facilitating hand-based interactions in applications such as prosthetics, virtual reality, robotic teleoperation, surface haptics, portable devices, and rehabilitation. This paper presents a systematic review and meta-analysis of electrotactile feedback systems for hand based interactions in the last decade. We categorize the different electrotactile systems according to their type of stimulation and implementation/application. We also present and discuss a quantitative congregation of the findings, so as to offer a high-level overview into the state-of-art and suggest future directions. Electrotactile feedback was successful in rendering and/or augmenting most tactile sensations, eliciting perceptual processes, and improving performance in many scenarios, especially in those where the wearability/portability of the system is important. However, knowledge gaps, technical drawbacks, and methodological limitations were detected, which should be addressed in future studies.

1 citations


Book ChapterDOI
01 Jan 2021
Abstract: To fully replace the missing limb, a myoelectric prosthesis needs to provide a bidirectional communication between user’s brain and its bionic limb. And indeed, modern prosthetic hands are advanced mechatronic systems that approach the design and capabilities of biological hands both morphologically (size, shape, and weight) and functionally (degrees of freedom). In addition, these hands are controlled intuitively by mapping muscles’ activations to prosthesis functions using direct control or pattern classification. However, commercial systems do not yet provide somatosensory feedback to their users. In this chapter, we provide an overview of the methods and techniques that can be used to stimulate the sensory motor structures of an amputee subject in order to restore the missing sensations. We then discuss the prosthesis variables that are most often transmitted through the stimulation as well as the encoding schemes that can be used to map those variables to stimulation parameters. The contradictory evidence about the impact of feedback on the prosthesis performance is presented next, illustrating that designing, implementing, and assessing effective feedback interfaces is indeed a challenging task. Finally, the chapter ends with discussion and recommendation for further research that will hopefully lead to a successful solution for closed-loop prosthesis control.

Journal ArticleDOI
Abstract: Aim Limb loss is a dramatic event with a devastating impact on a person's quality of life. Prostheses have been used to restore lost motor abilities and cosmetic appearance. Closing the loop between the prosthesis and the amputee by providing somatosensory feedback to the user might improve the performance, confidence of the amputee, and embodiment of the prosthesis. Recently, a minimally invasive method, in which the electrodes are placed subdermally, was presented and psychometrically evaluated. The present study aimed to assess the quality of online control with subdermal stimulation and compare it to that achieved using surface stimulation (common benchmark) as well as to investigate the impact of training on the two modalities. Methods Ten able-bodied subjects performed a PC-based compensatory tracking task. The subjects employed a joystick to track a predefined pseudorandom trajectory using feedback on the momentary tracking error, which was conveyed via surface and subdermal electrotactile stimulation. The tracking performance was evaluated using the correlation coefficient (CORR), root mean square error (RMSE), and time delay between reference and generated trajectories. Results Both stimulation modalities resulted in good closed-loop control, and surface stimulation outperformed the subdermal approach. There was significant difference in CORR (86 vs 77%) and RMSE (0.23 vs 0.31) between surface and subdermal stimulation (all p < 0.05). The RMSE of the subdermal stimulation decreased significantly in the first few trials. Conclusion Subdermal stimulation is a viable method to provide tactile feedback. The quality of online control is, however, somewhat worse compared to that achieved using surface stimulation. Nevertheless, due to minimal invasiveness, compactness, and power efficiency, the subdermal interface could be an attractive solution for the functional application in sensate prostheses.

References
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Journal ArticleDOI
TL;DR: The sensitivity of the projections to increasing or decreasing incidence was investigated, and alternative sets of estimates of limb loss related to dysvascular conditions based on assumptions of a 10% or 25% increase or decrease in incidence of amputations for these conditions were developed.
Abstract: Ziegler-Graham K, MacKenzie EJ, Ephraim PL, Travison TG, Brookmeyer R. Estimating the prevalence of limb loss in the United States: 2005 to 2050. Objective To estimate the current prevalence of limb loss in the United States and project the future prevalence to the year 2050. Design Estimates were constructed using age-, sex-, and race-specific incidence rates for amputation combined with age-, sex-, and race-specific assumptions about mortality. Incidence rates were derived from the 1988 to 1999 Nationwide Inpatient Sample of the Healthcare Cost and Utilization Project, corrected for the likelihood of reamputation among those undergoing amputation for vascular disease. Incidence rates were assumed to remain constant over time and applied to historic mortality and population data along with the best available estimates of relative risk, future mortality, and future population projections. To investigate the sensitivity of our projections to increasing or decreasing incidence, we developed alternative sets of estimates of limb loss related to dysvascular conditions based on assumptions of a 10% or 25% increase or decrease in incidence of amputations for these conditions. Setting Community, nonfederal, short-term hospitals in the United States. Participants Persons who were discharged from a hospital with a procedure code for upper-limb or lower-limb amputation or diagnosis code of traumatic amputation. Interventions Not applicable. Main Outcome Measures Prevalence of limb loss by age, sex, race, etiology, and level in 2005 and projections to the year 2050. Results In the year 2005, 1.6 million persons were living with the loss of a limb. Of these subjects, 42% were nonwhite and 38% had an amputation secondary to dysvascular disease with a comorbid diagnosis of diabetes mellitus. It is projected that the number of people living with the loss of a limb will more than double by the year 2050 to 3.6 million. If incidence rates secondary to dysvascular disease can be reduced by 10%, this number would be lowered by 225,000. Conclusions One in 190 Americans is currently living with the loss of a limb. Unchecked, this number may double by the year 2050.

1,865 citations


"The Variability of Psychophysical P..." refers background in this paper

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Journal ArticleDOI
TL;DR: The use of the staircase-method is illustrated, its relative merits and demerits are discussed, and a modification is described which overcomes certain of the disadvantages of the method.
Abstract: NOTES AND DISCUSSIONS THE STAIRCASE-METHOD IN PSYCHOPHYSICS A psychophysical method variously referred to as the method of up and downs, 1 the Bekesy audiometric method, 2 or the staircase-method, has come into extensive use in the last few years. The method has several advantages over other more commonly used techniques but it also has some disadvantages. This paper will illustrate the use of the method, will discuss its relative merits and demerits, and will describe a modification which overcomes certain of the disadvantages of the method. The staircase-method is best described by illustrating its use with a specific prob- lem. Suppose the problem is to determine S's absolute, intensive threshold for the sound of a click. The first stimulus that E delivers is a click of some arbitrary intensity. S responds either that he did or did not hear it. If S says 'yes' (he did hear it), the next stimulus is made less intense, and if S says 'no,' the second stimulus is made more intense. If S responds 'yes' to the second stimulus, the third is made less intense, and if he says 'no,' it is made more intense. This procedure is simply continued until some predetermined criterion or 'number of trials' is reached. The results of a series of 30 trials are shown in Fig. 1. The results may be recorded directly on graph-paper; doing so helps E keep the procedure straight. There are a number of ways of determining the intensive value that represents the threshold. The simplest is to compute the mean of the values of a given num- ber of stimuli delivered after the series has reached its final level. This requires an arbitrary decision about when the final level has been reached. The technique, which avoids this difficulty and yields a 50% value, is simply to determine the stimulus above which 50% of the responses are 'yes,'-i.e. in Fig. 1 between 61 and 62 db. Statistical treatment of the results has been discussed by Dixon and Massey, who describe the techniques for determining the means, standard deviations, standard errors, etc., for this type of data.3 The treatments assume, however, that the response to each stimulus is independent of the preceding stimuli and pre- ceding responses. This assumption holds for the examples analyzed, but there is evidence that the assumption does not always hold for human Ss in psychophysical experiments.• The development of techn.iques that take the existing inter-actions into account has not as yet been achieved. W. J. Dixon and F. J. Massey, lnt,.oduction lo Statistical Analysis, 1957, 279· •Georg von Bekesy, A new audiometer, A'la 010-/a,.yngol., 35, 1947, 411-422. •Dixon and Massey, op. cit., 286. • W. S. Verplanck, G. H. Collier, and J. W. Cotton, Nonindependence of succes- sive responses in measurement of the visual threshold, /. exp. Psycho/., 42, 1952, 273-282; Verplanck and Cotton, The dependence of frequencies of seeing on pro- cedural variables: J. Direction and length of series of intensity-ordered stimuli, /. gen. Psycho/., 53, 1955, 37-47; V. L. Senders, Further analysis of response se- quences in the setting of a psychophysical experiment, this JOURNAL, 66, 1 953, 215-229; R. S. Woodworth and Harold Schlosberg, Experimental Psychology, 1954,

1,162 citations


"The Variability of Psychophysical P..." refers methods in this paper

  • ...The DT was measured using a staircase method by delivering single pulses with an inter-pulse interval of 2 s [25]....

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Journal ArticleDOI
TL;DR: An analytical and comparative survey of upper limb prosthesis acceptance and abandonment as documented over the past 25 years is presented, detailing areas of consumer dissatisfaction and ongoing technological advancements.
Abstract: This review presents an analytical and comparative survey of upper limb prosthesis acceptance and abandonment as documented over the past 25 years, detailing areas of consumer dissatisfaction and ongoing technological advancements. English-language articles were identified in a search of Ovid, PubMed, and ISI Web of Science (1980 until February 2006) for key words upper limb and prosthesis. Articles focused on upper limb prostheses and addressing: (i) Factors associated with abandonment; (ii) Rejection rates; (iii) Functional analyses and patterns of wear; and (iv) Consumer satisfaction, were extracted with the exclusion of those detailing tools for outcome measurement, case studies, and medical procedures. Approximately 200 articles were included in the review process with 40 providing rates of prosthesis rejection. Quantitative measures of population characteristics, study methodology, and prostheses in use were extracted from each article. Mean rejection rates of 45% and 35% were observed in the literature for body-powered and electric prostheses respectively in pediatric populations. Significantly lower rates of rejection for both body-powered (26%) and electric (23%) devices were observed in adult populations while the average incidence of non-wear was similar for pediatric (16%) and adult (20%) populations. Documented rates of rejection exhibit a wide range of variance, possibly due to the heterogeneous samples involved and methodological differences between studies. Future research should comprise of controlled, multifactor studies adopting standardized outcome measures in order to promote comprehensive understanding of the factors affecting prosthesis use and abandonment. An enhanced understanding of these factors is needed to optimize prescription practices, guide design efforts, and satiate demand for evidence-based measures of intervention.

719 citations


"The Variability of Psychophysical P..." refers background in this paper

  • ...For upper limb prosthetic users, the absence of sensory feedback impedes the efficient use of their prostheses, which can lead to user frustration and abandonment of the device [2]....

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Journal ArticleDOI
TL;DR: This paper presents an overview of the principal works and devices employed to provide upper limb amputees with sensory feedback and the principal features, advantages and disadvantages of the different methods are presented.
Abstract: One of the challenges facing prosthetic designers and engineers is to restore the missing sensory function inherit to hand amputation. Several different techniques can be employed to provide amputees with sensory feedback: sensory substitution methods where the recorded stimulus is not only transferred to the amputee, but also translated to a different modality (modality-matched feedback), which transfers the stimulus without translation and direct neural stimulation, which interacts directly with peripheral afferent nerves. This paper presents an overview of the principal works and devices employed to provide upper limb amputees with sensory feedback. The focus is on sensory substitution and modality matched feedback; the principal features, advantages and disadvantages of the different methods are presented.

328 citations


Additional excerpts

  • ...stimulation methods to elicit tactile sensations [6]....

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Journal ArticleDOI
TL;DR: These findings support the hypothesis that population spike count drives the magnitude of tactile percepts and indicate that sensory magnitude can be manipulated systematically by varying a single stimulation quantity.
Abstract: Electrical stimulation of sensory nerves is a powerful tool for studying neural coding because it can activate neural populations in ways that natural stimulation cannot Electrical stimulation of the nerve has also been used to restore sensation to patients who have suffered the loss of a limb We have used long-term implanted electrical interfaces to elucidate the neural basis of perceived intensity in the sense of touch To this end, we assessed the sensory correlates of neural firing rate and neuronal population recruitment independently by varying two parameters of nerve stimulation: pulse frequency and pulse width Specifically, two amputees, chronically implanted with peripheral nerve electrodes, performed each of three psychophysical tasks-intensity discrimination, magnitude scaling, and intensity matching-in response to electrical stimulation of their somatosensory nerves We found that stimulation pulse width and pulse frequency had systematic, cooperative effects on perceived tactile intensity and that the artificial tactile sensations could be reliably matched to skin indentations on the intact limb We identified a quantity we termed the activation charge rate (ACR), derived from stimulation parameters, that predicted the magnitude of artificial tactile percepts across all testing conditions On the basis of principles of nerve fiber recruitment, the ACR represents the total population spike count in the activated neural population Our findings support the hypothesis that population spike count drives the magnitude of tactile percepts and indicate that sensory magnitude can be manipulated systematically by varying a single stimulation quantity

151 citations


"The Variability of Psychophysical P..." refers background in this paper

  • ...This was likely due to the subject getting used to the sensations elicited by the two types of stimulation [29], [30]....

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Frequently Asked Questions (2)
Q1. What are the contributions in this paper?

This study investigates the multiday variability of subdermal and surface stimulation. The outcome of this study has implications for the choice of modality in delivering sensory feedback, though the significance of the quantified variability needs to be evaluated using usability tests with user feedback. 

Hence, the present study provides important information for future clinical applications of this approach.