Final report Jeanne Pigassou: Robotic device for assessing touch sensitivity in autistic children using NIRS and fMRI

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Robotic Device for assessing
sensitivity to touch using NIRS
and fMRI in autistic children

September 2012

Jeanne PIGASSOU

Supervisor: PHD Alessandro Allievi

Co-Supervisor: Pr. Etienne Burdet

Submitted in partial fulfilment of the requirements for the award of MSc in Biomedical
Engineering and the Diploma of the Imperial College

Abstract

Imperial College London jeanne.pigassou11@imperial.ac.uk

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Autism is usually diagnosed after 2 years of age, when behavioural, sensory and communication symptoms are
sufficiently clear. Yet an early detection of autism is crucial to help devising appropriate therapies in order to
reduce autistic disorders. Autistic children are often affected by hypotactility or hypertactility, sensitivity
abnormalities that make them react unusually to tactile stimuli reproducing the touch of another person. This
project designed a robotic device to assess the reactivity of children at risk of developing autism to “social
touch”. The reaction of infants to a paintbrush stroke yielding a “social touch” was observed using NIRS or fMRI,
two imaging techniques that display cerebral activity. Here, an automated pneumatic piston, moving at various
speeds, commands the paintbrush stroke. Different stimuli frequencies allowed us to study the baby’s
habituation to the touch. The device was designed to fit on any limb of an infant, to test different touch-sensitive
body areas.


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Acknowledgements

I am aware that this project could not have been completed alone, and would like to thank everybody who
helped me during this adventure. My special thanks go to my supervisors Alessandro Allievi and Dr. Etienne
Burdet for their support and help on this innovative project. Thank you Alessandro Allievi for your availability,
technical help and for your unfailing good humour. I am also very grateful to Pr. Mark Johnson, Dr. Teodora
Gliga and Sarah Lloyd Fox of CBCD for their motivation, help and involvement in this project. I hope this project
will help them in their BASIS study. Nick Everdell of UCL, and Anna Blasi of CBCD, thank you so much for
helping me with the NIRS machine. I do not forget the help of Dr. Tomoki Arichi from Hammersmith Hospital, Dr.
Alejandro Melendez Calderon from Imperial College and Maria Laura Filipetti from CBCD, and all the members
of the Human Robotics group, thank you too. This many-sided collaboration with the Bioengineering
Department of Imperial College and the Centre for Brain and Cognitive Development of Birkbeck University gave
me a unique opportunity to discover and enjoy working in a research environment.


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Table
of
Content

Abstract
.........................................................................................................................................

1

Acknowledgements

.........................................................................................................................

3

1.
Introduction……………………………………………………………………………………………………………………………………..5

1.
1
Autism………………………………………………………………………………………………………………………………….5

ASD…………………………………………………………………………………………………………………....………….5

Sensitivity
to
touch
…………………………………………………………………………………………….………….5

Diagnosis…………………………………………………………………………………………………………….………….6

1.2
Objectives………………………………………………………………………………………………………………..…….…….6

1.3
Contribution…………………………………………………………………………………………………………….…………..7

1.4
Scanning
Techniques……………………………………………………………………………………………....……………7

NIRS……………………………………………………………………………………….............................………….7

fMRI
………………………………………………………………………………………...........................…………..7

1.5
Challenges……………………………………………………………………………………………………………….……….….8

Literature
Review….…..…………………………………………………………………………………………………..8

Device
development
…….…………………………………………………………………………………….………….8

Evaluation
of
Results………………………………………………………………………………………….…………..9

2.
Material
&
Methods…………………………………………………………………………………………………………….……………10

2.1
Main
Device
…………………………………………………………………………………………………………..…………..10

2.2
Design
of
the
device………………………………………………………………………………………………..…………..11

The
piston………………………………………………………………………………………………………….………….11

The
sensor…………………………………………………………………………………………………………………….11

The
paintbrush
…………………………………………………………………………………………………………….14

The
cushion
………………………………………………………………………………………………………………….14

2.3
Control
and
synchronization………………………………………………………………………………………………..15

The
valves
………………………………………………………………………………………………………..………….15

Calibration
of
sensor
………………………………………………………………………………………..………….17

2.4
Program
……………………………………………………………………………………………………………………………..19

fMRI
program……………………………………………………………………………………….............………….20

NIRS
program……………………………………………………………………………………….............………….21

3.
Results
………………………………………………………………………………………………………………………………..…………..23

3.1
Preliminary
tests…..…………………………………………………………………………………………………………….23

The
cushion………………………………………………………………………………………................………….23

The
paintbrush………………………………………………………………………………………...........………….24

Speed……………………………………………………………………………………….........................………….24

3.2
fMRI
test
on
adult.………………………………………………………………………………………………………………25

3.3
Safety
Measures
..……………………………………………………………………………………………………………….26

Hardware…………………………………………………………………………………………………………………….26

Software…….……………………………………………………………………………………………………………….26

4.Discussion

………………………………………………………………………………………………………………………….…………….28

4.1
Choice
of
equipment
…………………………………………………………………………………………….……………28

The
piston.………………………………………………………………………………………................…………..28

The
sensor……………………………………………………………………………………….................…………..28

4.2
Imaging
techniques
……………………………………………………………………………………………………………28

5.
Conclusion
……………………………………………………………………………………………………………………….………………29

References
…………………………………………………………………………………………………………………………..………………30


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1. Introduction

1.1 Autism

• Autistic Spectrum Disorders

Autistic Spectrum Disorders (ASD) are developmental conditions affecting communication and social
development. A modification of the organization of the neural network during the development affects
information processing of the brain, leading to a repetitive and restricted behaviour. The International
Classification of Diseases describes children with a cluster of symptoms that vary widely in type and severity.
The symptoms are grouped into three broad categories: (1) qualitative impairment in social interaction, (2)
communication disorders, and (3) stereotyped, repetitive patterns of behaviours or a restricted range of interests
[1]. Depending on the level and distribution of impairment across these categories, a child can be diagnosed
with one of the following ASD: Autistic Disorder, Asperger syndrome, or Pervasive Developmental Disorder.

Yet, for all these types of ASD there are some similar symptoms, including sensory abnormalities. Several
studies have proven that there are executive dysfunctions in autism and it was demonstrated in many ways: E.
Hill listed and evaluated the studies in [2]. These movement disorders are due to a low level of neuronal
connections, even though it is not clear what part of the brain is involved, as explained in [3], [4], and [5].

Because autism has a strong genetic basis, the risk of autism is higher when one sibling is already affected (2 to
18%) and even higher when they are twins (0-31% for non-identical twins, and 36 to 95% for identical twins).
That is why siblings of autistic children have to be watched over to detect autism disorder early. Furthermore,
the probability of ASD increases if the parents are old and if they already have genetic or chromosomal
conditions [6].

• Sensitivity to touch

Along with socialisation and communication impairment, autistic children often show sensitivity abnormalities [7].
Their senses - touch, smell, taste, hearing, vision, but also vestibular and proprioceptive senses- can be either
hypersensitive, or on the contrary hyposensitive. A study showed that 39% of children with ASD are underactive
to sensation, 20% are oversensitive and 36% show a mixed pattern of both under and over reactivity [9].

Hypotactility means that the child is under-sensitive to touch stimuli. Such children will not be able to feel light
touches, but also high temperatures and pain. To stimulate their underactive senses they will show violent
movements that could hurt themselves. [30]

Hypertactility happens when a child’s tactile awareness is too acute. Even a gentle touch can be uncomfortable
or painful to them. They may also dislike the sensation of hot and cold: touching something hot or cold, but
even feeling warm and being cold. [31]

Moreover, a recent study showed that autistic traits are associated with diminished neural response to affective
touch [10]. One interpretation raised is that “the brains of people high in autistic traits aren’t coding touch as
socially relevant”. Indeed, the affective aspect of touch plays a prominent part in social interactions, and an fMRI
study [11] proved that the temperature of the brain changes when the patient is touched with a neutral, pleasant
or painful stimuli.

• Diagnostic

Autism affects about 1 in 100 children [8], but this figure changes when taking into account different disorders.
Parents usually discover the first symptoms of autism during the first two years of the child’s life, but for the time
being, a reliable diagnostic can only be made after 2 years of age. Currently, as there is no medical test to
diagnose ASD, the diagnosis is based on the observation and the interactive dialogue with the child to assess

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his communicative and social capacities, as well as on structured questioning of the parents about the child’s
development, his behaviour and interactions [12]. There is no biological test available at the time being, but
thanks to a list of informative questions about the child, the M-CHAT (Modified Checklist of Autism in Toddlers),
an early detection of autism is possible at 18 month of age. To confirm this diagnosis, a further evaluation
initiated by a specialist (developmental paediatrician, or psychiatrist) is necessary. The thorough diagnosis
consists of a test by a psychiatrist, a check-up by a speech therapist, and a psychomotor check-up. Genetic
testing is also recommended to detect some genetic disorder leading to Persuasive Developmental Disorder, a
neurobiological examination could also determine if the child is epileptic, and sometimes an MRI scan is
performed to search for any visible abnormalities in the brain.

Thus autism is detected when the symptoms are sufficiently clear, yet the age varies a lot, as ASD spectrum is
very large. Still an early detection and early treatment of autism stands the greatest chance of positively
impacting a child’s development.

1.2 Objectives

The objective of this project is to create a robust and repeatable method to assess the sensitivity to touch of
toddlers, and also to see their reactions to a “social touch”. The cerebral activity of the patient during the stimuli
is to be recorded via NIRS or fMRI. The device has to reproduce “social touch” on a baby’s arm or any other
part of the body highly sensitive to touch. The movement also has to be operated at various speeds and the
block of stimuli could be repeated at different frequencies.

The results of this test could lead to an early diagnosis of ASD as it would be performed on children with higher
risk of autism. A robotic device is highly suitable for this application, as this type of study requires exact
repeatability of the stimulation paradigm to obtain significant population results. Several studies about sensitivity
to touch by brushing a patients arm and screening the cerebral activity have already been made [10] but none
of them used a robotic device, thus failing to guarantee that the experiment was carried out in an objective and
repeatable manner.

1.3 Contribution

This study was carried out in collaboration with Professor Mark H. Johnson, Dr Teodora Gliga and PhD Sarah
Lloyd Fox from the Centre for Brain and Cognitive Development. Research driven by CBCD members concern
visual, cognitive and language development in human infants, children and adults by using converging methods:
behaviour testing, eye tracking, Event-Related Potentials, Electroencephalography, optical imaging including
NIRS, computer modelling, functional and structural MRI. One of their three laboratories, the Babylab, focuses
on typical, at-risk and atypical brain and cognitive development over the first years and they have developed
optical imaging methods (NIRS) in collaboration with UCL for studying brain functions in infants.

Professor Mark Johnson, director of the CBCD and MRC Team Leader, dedicates his research to the
understanding of the specialisation of cortical areas for a perceptual and cognitive function unfolds during
postnatal development. A major empirical project has been the large-scale longitudinal study of babies at risk of
autism (BASIS - British Autism Study of Infants Siblings), yielding valuable information about the typical and
atypical development of the social brain network [13].

Dr Teodora Gliga is an MRC Research Fellow whose research focuses on the development of human
communication skills. She is also exploring the origin of communication difficulties in autism spectrum disorders.

Research Fellow Sarah Lloyd Fox‘s research focuses on the development of infants' social cognitive abilities
over the first year of life. Using the neuroimaging technique of NIRS, she investigates cortical responses to the
perception of social and human action cues.


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This project is intended to help their investigations in the BASIS, looking for early signs of autism. The projects
included in this study are mainly concerned with social interaction: visual, auditory, and also tactile, but olfactory
and taste senses are more difficult to quantify. CBCD research fellow Maria Laura Filipetti is also working on a
project concerning the reaction to “social touch” of babies using paintbrush stroke stimuli, but so far without a
robot.

1.4 Scanning techniques

The analysis of cerebral activity in toddlers via imaging is already well advanced, as it is of considerable
importance in toddler’s examinations. The challenge is to use a scanner precise enough to see any change or
abnormalities at a very small scale, while being safe enough to avoid any hazardous radiations. To be able to
see activity in the brain, the scanning technique must be functional and fast. Two scanning techniques meet
these requirements: the Near Infra-Red Spectroscopy (NIRS) and the functional magnetic Resonance Imaging
(fMRI).

• NIRS

NIRS is a spectroscopic method based on the absorption properties of the electromagnetic spectrum (in the
near-infrared region). By using a banana-shaped beam of near infrared light, passing through organic tissues, it
is possible to measure the absorption and the dispersion of photons. Thanks to the Beer-Lambert law, the
concentration of the absorbing substance is calculable from the absorption of the light. The oxygenated blood
to deoxygenated blood ratio gives information about the brain activity. Indeed, oxygenated blood contains O2
saturated haemoglobin (Hb), optimally absorbed at 810 nm, while non-saturated Hb (optimally absorbed at 780
nm) is majoritarian in deoxygenated blood. In a functionally activated cortex area, the localized blood volume
changes quickly, thus saturated and non-saturated Hb absorbs more light. During a NIRS experiment, an array
of optic probes is placed on the patient’s head. Half of the probes emit light, the other half of the probes serves
as a detector that absorbs reflected light. The emission probes emit light at two specific frequencies: 380nm
and 780nm [14]. CBCD has constructed a NIRS machine in collaboration with University College London,
especially designed for babies. The cap fits to a child’s head and there are a limited number of electrodes to
lighten it. Figure 1.

• fMRI

The physics of magnetic resonance imaging depends on magnetic properties of water contained in the human
body. If an external magnetic field is applied these H2O protons align themselves to that field, wobbling about
the field axis. This precession creates an electromagnetic signal that can be measured. When a second
magnetic field, in the form of a radiofrequency (RF) pulse, is applied at right angles to the first, the protons’
vector alters to become perpendicular to the external magnetic field, and they gain energy and spin
synchronously: they are “in phase”. Once the RF pulse stops, the protons shed their extra newly acquired
energy back to the surrounding chemical lattice (T1 relaxation), and simultaneously, they stop spinning
synchronously (T2 relaxation). T1 and T2 periods depend on their spatial location and the nature of the chemical
composition of the proton. Thus a 3D image of the biological tissues explored is obtained. Functional MRI is a
non-invasive method of studying brain function. It permits the visualisation of areas of the brain, which have
responded to a specific task or stimulus. Indeed, it monitors indirectly the haemodynamic response to brain
activation. Increased oxygen fraction in the blood caused by local neuronal activation reduces the paramagnetic
effect of deoxy Hb causing a signal increase on T2 weighted images. The response lags the neuronal firing, by
several seconds. [15], [16] (Figure 2).


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Figure 1 : NIRS cap Figure 2: baby in fMRI scanner

1.5 Challenge

• Literature Review

To date, most studies on autism have not focused on this specific subject, but addressed questions about the
behaviour, the somatosensory capacities or the brain activity of autistic children and adults. As ASD is
considered as a mental disorder, assessment of autistic perception is mainly done using psychic tests, not with
imaging analysis. These readings clarified some key points, presented below.

There are very few studies on autistic babies as ASD is usually diagnosed after two years of age, when a child
begins to mix with other children and adults. Yet in [17], the behaviour of autistic infants is analysed thanks to
video recordings of the child’s firsts months. The authors could confirm that autistic babies had, among others,
abnormal gesture and movement coordination.

Furthermore, even though some papers concerned brain fMRI analysis of autistic children, the conditions of the
experiment were very different from the course of the tests of the project. Indeed, these studies involved a
motor action resulting from a verbal or visual command as in [18], so this protocol cannot be applied to autistic
babies and does not give any information about passive movements.

One major difficulty researchers encounter is the evaluation of the degree of autism affecting patients because
there are various forms of ASD as explained in [19]. In many studies especially in Staples’ study [20], authors
tried to rate the patients after the level of their disorder, but they diverged upon the manner of ranking: IQ,
equivalent age etc. Hopefully, this problem may not be encountered, as the patients will be young enough to
assume the stage of the disease is the same for all of the babies.

• Device development

The main challenge of this project was to conceive a device safe enough to go inside the MRI scanner with the
baby. While robotic tools used with an MRI scanner are compatible (e.g. for safety issues, there is no
ferromagnetic material in it and they do not create any image artefact [32]). Yet it is not safe enough to be used
in a baby fMRI scan: the device will be placed inside the head coil with the baby. Thus there should be no metal
such as aluminium to ensure that there will be no overheating or magnetic attraction to the MRI machine
magnet.

Furthermore, as the device is intended for babies, its dimensions must be adapted to their small size. It is
difficult to achieve a reasonable precision for a hand made prototype of such a small device: some elements of
the device are given with a 0,1 mm accuracy

A further challenge resides in the capacity to control remotely the device attached on an infant’s limb. The
smoothness and safety of the control are key elements to the conception of the device. The stimuli must be


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slow enough to be used on a toddler, yet the stimulus’ amplitude has to be large enough to assure good
cerebral response.

• Evaluation of Results

The evaluation of the results will be supported by the fMRI images and NIRS data obtained during the
experiments. Thus it will give quantitative information, contrary to the qualitative assessment seen in the majority
of the paper concerning this subject.

The results obtained should be compared to the ones of a normal population to detect any irregular neural
activity. If autistic children of more than 3 years old are tested, the results may be harder to evaluate, as the level
of the autism could be different for each patient.

A Preliminary test on adults without imaging will help to determine the final version of the device.

As the proportion of autistic infants is small, a large number of results will be needed to draw a conclusion
concerning an early diagnostic of autism.


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Materials & Methods

The project can be divided in three stages of equal duration each, as they all bear equal importance:
background research, experiments, and elaboration of the report. The planning of the project was also marked
by two deadline dates: handing of reports, and end of the authorization of experiments.

The period of research is much longer than the other ones. Indeed, the long discussion with the psychologist
team of CBCD, helping us with the understanding of autistic disorders and setting the requirements of the
device was a necessary step to undertake.

The second step includes the determination of the experimentations’ methodology, design and construction of
the device and the experimental stage. The robotic device has to be able to monitor some easy movements to
stimulate a tactile feeling on a limb of the baby. The device can be designed for the arm, the hand or the leg as
it is easy to attach a device on a limb. Most important, the device has to be MRI safe: no metal should be used.
Thus, it will be made of plastic, with pneumatic or hydraulic motorization.

Main device

To ensure smooth function of the whole device, the valves had to be timed and organized correctly, along with
the regulators and the optic sensor. Figure 3 shows a block diagram of the layout of all of the components.

• The combination of a paintbrush and pneumatic piston creates the social touch stimuli

— Optic fibres together with a mirror builds a position sensor thanks to the reflexive property of light

— The DAQ permits to monitor the analogue input and the digital outputs.

— The Labview program controls the valves and records data from the sensor.

A stop button has been added on the top of the box to handle emergencies. Figure 4. When the normally close
stop button is activated, the power is not anymore given to the valves, which immediately stops working and as
a result the participant is protected of any abnormal activity of the valves. Furthermore, there is two switches to
control the power supply to the valves and to the sensor: they can be used individually.

The data acquisition card deals with the input and output of digital and analogue signals. It can convert
analogue waveforms into digital values for processing, such as with the data from the optic sensor. It can also
receive digital values as for the MRI synchronization binary signal; or can produce digital output of 3,8V at 6mA
as for the control of the valves.

All the components have been installed in a box to ensure a portable and safe device. These valves are
controlled using the Labview software via a data acquisition card (DAQ). In order to automate the shifting of the
piston, a control program has been incorporated to this project. The Labview program also allows the
synchronisation of touch stimuli with the NIRS images.


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Figure 3: Block Diagram of the layouts of the components Figure 4: Control Box

Design of the device

After some discussion with the team of CBCD we settled the purpose and gross design of the device. We want
to assess the reaction of autistic children to social touch, by simulating the stroke of a hand at different speeds
and frequencies. Indeed, the variation of velocity could help detect the threshold of recognizing a social to touch
from a normal touch. The changing frequency of the repetition of the stimulation block can help determining
after how many touches an autistic child becomes hyposensitive: he would not react to social touch any more.

Research has proven that the best manner to reproduce social touch is by stroking gently with a paintbrush
[10], [21]. The brushing movement back and forth has to be regular, and the velocity must be controlled. The
device has to be small enough to be attached on a baby’s arm or leg to test different sensitive parts of the
body.

The solution found to fulfil these requirements was to use a pneumatic piston of 1.5cm range with a paintbrush
at its end (Figure 5). Two digital valves that can be commanded through a DAQ control the piston, and a sensor
composed by an optic fibre and a mirror gives the position and the speed of the piston.

Figure 5: Final Paintbrush device

• The piston

A motor could not impose the movement of the paintbrush because this device has to be MR safe. As it may be
used inside an fMRI scanner, no metal piece is allowed, and this is why a piston was chosen to monitor the
stroke of the water brush. It can be pneumatic or hydraulic, but as it also has to be non-magnetic, drastically
reducing the choice of the piston. Furthermore, the size of the piston is important, as it has to be small enough
to be used on a baby’s limb.

The solution found is a pneumatic Lego piston made of plastic. This piston is air controlled, it was chosen over a
hydraulic piston as the management of oil circuit is more complex. The air output can be supplied by a common
air output or by an air compressor. Moreover the dimension of this Lego piece matches the required size. One
last advantage is that it is easy to build a sensor or a paintbrush tip with other Lego pieces because they suit
into the holes of the piston.

• The sensor

The sensor used has to be non-magnetic like the rest of the device and it has to give information about the
position of the paintbrush. Here, an optical sensor was constructed by using two optical fibres, an optic sensor
[22] and a mirror (Figure 6). By using the reflexive property of light with the optic fibre in this device, the sensor
has to fulfil two more conditions: be dark to avoid external light to interfere with the optic fibre, and be small
enough to be well inserted on the piston.


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Figure 6: Scheme of the sensor

Two glass optic fibres (GOF) of 1mm diameter are used with an amplifier: one sending IR light, the other
receiving it. Both are glued inside a horizontal rod of 6mm diameter fixed on the immobile end of the piston
thanks to a Lego piece. The light is transmitted between the two fibres thanks to a vertical mirror of 6mm
diameter on the mobile end of the piston. A small tube of the same length as the range of the piston
approximately, and of the same internal diameter than the rod is glued horizontally on a Lego piece, with a
round mirror at its end. The dimension of the optic fibre was chosen so that the intensity of the receiving fibre
was high enough for the sensor, whatever the position on the mirror. Smaller optic fibres (980µm Ø)
were tested
unsuccessfully; the variation of intensity was not measurable by the sensor.

The two fibres can be considered as horizontal, parallel and very close together. The mirror is also vertical,
perpendicular to the two optic fibres. Other positions of the mirror and the fibres are possible to obtain an
optical position sensor [23] (Figure 7), but the small dimensions of our sensor led us to prefer this one. The
intensity of the light reflected by the mirror depends on the distance between the mirror and the end of the fibre,
hence of the position of the piston here. The relationship is nonlinear as the intensity of the light is a combination
of sine waves of the position of the mirror.

Figure 7: Different configurations possible for an optic sensor

One difficulty in the construction of this sensor is that the minimum of range of the piston has to coincide with
the maximum of intensity of the sensor. If the relationship between the displacement and the voltage output is
not injective, one voltage output could give several positions. That is why several dispositions of the mirror and
the fibres were possible but considering the size of the rod, mirror and optical fibre used it was very difficult to
arrange an angle α 1 or α 2 between the two fibres or an angle β between the mirrors and the Lego piece that
could be precisely constructed and measurable. Furthermore, as the distance between the mirror and the fibres
varies from 0 to 1.5cm, the two optical fibres have to be very close together. Indeed, at position 0, the light
reflected by the mirror is next to the emitting fibre, so the receiving fibre has to be just next to the emitting one.

Several designs of the sensor were realized: using a syringe (Figure 8), a rod and bearing, or even another
piston (Figure 9). The combination of a pierced rod and a matching bearing gave the best results for the sensor
output, which is why it was finally chosen.


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Figure 8: initial syringe( top) Figure 9: scheme of sensor integrated in the piston (top)
and final syringe sensor ( bottom) and constructed device (bottom)

Here, a 3mm diameter hole was pierced inside the 6mm diameter dark nylon rod and used to support the
fibres. One fibre was stripped form the plastic protection, the other was left with it and both fibres are
introduced and glued inside the hole of the rod. This solution was the only way to obtain very narrow optic
fibres, as it is very difficult to pierce two 1mm diameter and 1.5 cm long holes inside a dark nylon rod of 6mm
diameter. The holes were either in diagonal or too spaced. Here are various pierced rods that have been tried.
Figure 10.

Figure 10: Different rods pierced with optical fibre inserted

Concerning the other part of the sensor, some difficulties were also met. First the choice of the mirror: it cannot
be ferromagnetic, this means that the reflecting layer must be in silver or aluminium. The mirror should also fit
inside the tube: it can be either a square of less than 6mm width or a disk of 6mm diameter maximum. These
dimensions are very uncommon to the mirror industry, so to obtain such mirror, a plastic mirror normally
supposed to replace car mirrors was used. It was cut using a Stanley cutter or a hole-puncher of the desire
diameter. Several diameters of mirror were tried for the sensor, but the smaller the mirror, the less light is
reflected. Figure 12. Thus the optical sensor does not work well for small mirrors. The tube fixed on top of this
mirror had to suit perfectly to the rod, be long enough (1.5cm at least), of reasonable thickness and dark (to
avoid any interfering light). Here, Igus bearings were used, the dimensions matched perfectly and the sliding is
very easy thanks to the special coating of Igus. Two Igus bearings of 6mm inside diameter were tested, the XFM
and the GSM. The first one was 17,5mm long and 0,5mm thick: the thin walls of this tube permitted to obtain a
small sensor but after several tests it appears that it was not long enough: the sensor bent when the piston was
at its maximal range. This is why the second Igus bearing was used, it measures 20mm long and its outside
diameter is 7mm; it is indeed more voluminous but there is no bending whatever the position of the piston.

Figure 11: Reflecting part of the sensor from above (left), and from profile ( right )


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Figure 12: different size of mirror- 6mm(left) and 4mm(right)

• The paintbrush

The first idea was to buy a plastic paintbrush and to cut the handle to glue the brush on the piston. Yet plastic
water brushes are difficult to find, most of them are designed for children so the hairs are quite stiff. Yet the
main characteristic of the paintbrush was that it had to be very soft because it has to mimic social touch on a
baby’s skin (Figure 13).

So the hairs of an acrylic paintbrush were used to create a new Lego paintbrush: the hairs of the original
paintbrush were cut and glued inside of a Lego piece of the desire shape and size. There was a discussion with
Laura Filipetti, PhD at CBCD, whose project also includes paintbrush strokes stimuli, concerning the type of
water brushes to use: a flat one or a round one. No information is given about it in the papers using water brush
strokes. The round one could represent better a finger, but a flat brush has a larger contact.

Another paintbrush tip was constructed using a squirrel hair paintbrush. In this case as the hairs of the water
brush were glued to the handle and protected by a plastic film and several steel wires, it was easier to transform
it into a non-magnetic brush. The steel wires were removed and replaced by cable ties, and the handle was
sawed at its base to obtain a small brush.

Figure 13: squirrel paintbrush tip (left), plastic (yellow) and acrylic (white) paintbrush ( right)

• The cushion

The cushion, made of foam covered with fabric, is used to apply the device at the correct distance from the
skin, so that only the tip of the paintbrush touches. It holds on the baby’s limb with adjustable straps and, thus
case of emergency, it is easy to remove the device from the infant. The soft side of the strap is in contact with
the skin to avoid irritation.

The piston is placed on a half cylinder in plastic glued to the cushion, with two little notches for the air inputs of
the piston. The shape of the pillow is important, as it has to be large enough to be stable, but short enough to
leave the mobile tip of the piston free. The height of the cushion is also measured: it should not be too high to
gain in stability. Furthermore, the pillow should also have a notch so that the air tubing remains horizontal.

There are two possible positions of the strap on the cushion: either it is stitched to the bottom of the cushion, or
to its lateral sides. These two positions were tested but the second solution was abandoned after some testing
as the patient could feel jolts due to the air flowing in and out the tubing. Figure 14.


15

Figure 14: cushions with straps on bottom (left) and on the side ( right)

Control and Synchronisation

• The valves

An on/off digital pneumatic valve permits to control the air coming into the piston directly to a DAQ. Several
configurations with one or two valves, 2-port or 3-port valves were tested to monitor the piston. A 2-port valve
[24] has two ports -one for air entry, one for air output- and has possible states: open (on; the air flows) or
closed (off; the air does not flow). A 3-port valve [25] has three tubing outputs called A, B and C, and two
possible states: either A is connected to B (on), or A is connected to C (off). Here, A was connected to the
piston, B to air output through the regulator, and C to atmospheric air through a silencer. A manual pressure
regulator is inserted before the valve to control the pressure of the air coming in.
Indeed the compressed air
used is at six (or four for the air compressor) atm, which is too high for this application that needed only
approximately four atm.

On a first test, one on/off digital 2-port valves was used in combination with an elastic band attached from the
fixed part of the piston, to its mobile part, see Figure 15. The elastic band smoothens the forth movement when
the valve is on, and when it is switched off, the force applied on the tip of the piston draws the piston back in its
initial position. This configuration worked well, yet it was not the final one as it did not fulfill the original condition
that the speed should be controlled. Indeed, the problem of the elastic band – one valve combination is that the
back displacement of the piston is only determined by the strength of the elastic band.

Figure 15: configuration with an elastic band and one valve

To control the speed of the back way, the solution chosen was to remove the elastic band and to use a second
valve to control the back way of the piston. First, two 2-port valves were used. This configuration did not work
as air was blocked inside the piston after the first activation of one of the valves. Because when one valve is
switched on, while the other is off, the air at the pressure imposed by the regulator occupies the whole tubing,
and the piston. When the valve is turned off, the air at high pressure is blocked inside the tubing and piston.
When the second valve is switched on, high-pressure air is supposed to flow inside the piston, and shift it. Yet,
as the air inside the other part of the piston is uncompressible, the volume occupied cannot be reduced and it is
impossible to move it.

That is why we used a 3-port valve to replace one of the 2-port valves. Figure 16 left. On the 3-port valve, the
tubing is linked to the atmospheric air for the off position: this way, when the valve is on position off, no air is


16

blocked inside: it flows out. With this configuration, it is possible to move the piston back and forth, at the
condition that the two valves must have antagonist commands: when one is switched on, the other must be off.
If not, air will be blocked inside the piston and the shifting is not possible anymore. Yet, this arrangement was
not satisfying because it was only possible to control the frequency of the motion, not the speed. Indeed, it is
possible to change the speed of shifting by modulating the air input. If the valve is switched on following a
square wave of given frequency and duty cycle α, it is possible to obtain different mean velocities Vmean of the
piston knowing the maximum velocity Vmax: Vmean=α* Vmax . To control the piston this way it is necessary to be
able to stop the piston in its stroke and start it again, i.e. to switch one valve on, off and on again while the other
valve remains closed. And this not possible when using a 3-port valve and a 2-port valve together.

Figure 16: control box using one 3-port valve and one 2-port valve (left) or two 3-port valves (right)

The last solution is to use two 3-port valves to control the piston. With this configuration, it is possible to stop
and restart a valve during its stroke while the other one is off. The command of the valves is the same as
described above. Every 2 seconds, when it is certain that piston has reached its limit range, the inputs of the
valves are switched. The input square wave of the valves can be represented on Figure 17. The duty cycle must
be quite high (> 70%) and the frequency high enough (>15Hz) to be able to stop the piston during its stroke. If
the frequency is too low, the period the piston stops may be too long and the sensation of mean velocity during
the whole displacement of the brush will be lost. If the duty cycle is too low, the piston will have time to move
the whole range before it is stopped, and the velocity is not tampered. By changing the duty cycle and/or the
frequency, the piston can move with different mean velocities. Yet, two limitations have to be taken into
account. First, the valve has a response delay of 30ms, thus, it is not possible to have a frequency superior to 1/
0,03 = 30Hz. Moreover, it was proved during the trials that high duty cycles are not compatible with high
velocities.

Figure 17: input square wave of the valves
The valves are powered by 24V using a converter that converts mains electricity of 240V alternating current (AC)
down to 24V DC. The state (open or close) of the valves is controlled by the value (True or false) send by the
data acquisition card [26]. However, the maximum DAQ digital data output is 3,8V at 6mA. A circuit is needed
to convert the 3,8V into 24V while keeping a minimal current. To do so, a Darlington Pair circuit has been used
(Figure 18), as the gain is squared, without drawing too much current. Indeed a Darlington Pair is made up of
two NPN transistors connected on top of each other, both sharing the same collector, resulting in a high current

17

gain. Each of the two valves has its own Darlington pair circuit as shown in Figure 19. For safety reason, a fuse
is added between the resistor and the Darlington pair. The fuse limits the current below 250mA, acting as a
protection for the DAQ. If the current exceeds this limit, the fuse blows and the DAQ is not damaged. The value
of the resistor has to be chosen to match with two conditions: the base current ib should be below 6mA (DAQ
limit) and the collector current ic should be below 250mA (fuse limit). A 10kΩ resistor was finally chosen. The
measured voltage at the terminals of the resistor was 2,44V and so the base current 0,244mA, which meets the
condition. Moreover, the collector current was measured as 0,185A. The gain is then: β=ic/ib=758, which is
consistent with the range of value [200, 1000] indicated in the datasheet. The different components of this
circuit have been soldered on a strip board. Connectors for the two valves, the sensor cable and the DAQ have
been added. [27]

Figure 18: Strip board Figure 19: Scheme of integrated
Darlington pair

• Sensor calibration

The optical sensor gives a voltage proportional to the incoming light as an output. This voltage can be read
thanks to the analogue input of the DAQ. Yet, the data have to be transformed because it is only plotting the
intensity received by the fibre. To obtain information about the position of the piston, the sensor has to be
calibrated. Moreover, to eliminate the most noise possible data from the optic sensor are filtered. A type 1
Butterworth first order filter with 0,5Hz cut-off frequency is applied.

A position sensor [28] is used in parallel to the optical sensor to perform the calibration. Here, an encoder was
used instead of a position sensor: it measures angles, not longitudinal displacements. To transform the
translational move of the piston into a rotational one, a matching toothed wheel and ladder are necessary. The
toothed wheel used is a common Lego piece. By piercing a little square of nylon with two holes of the size of
the encoder tip and the wheel tip, it was easy to make wheel and encoder interdependent. Lego ladders
matching with the toothed wheel exist but here one was constructed piece by piece by gluing several Lego
railings together. The dimensions between the sticks suited to the wheel, and thus a ladder of the desired
dimensions was created: the length of the ladder is equal to the range of the piston. Furthermore, as the ladder
was made of Lego pieces, it was easy to attach it to the moving tip of the piston (Figure 20).


18

Figure 20: Installing for sensor calibration

The calibration Labview program written with the help of Alessandro Allievi [29] allows the visualization of both
data obtained by the encoder and by the optic fibre.
The optical fibre sensor used was calibrated using a 360
pulses per revolution (0.25° resolution used in x4 mode) rotary encoder. In this program, data from both
encoder and optic sensor are acquired simultaneously and a XY graph representing the angle in function of the
voltage is drawn. The least squared error function of Labview is used to determine the polynomial of definite
order that fits best to this XY graph. The interface was first operated manually by displacing the piston back and
forth slowly during at least 10 seconds. Wiring the piston air inputs to the valves and operating the device at
varying frequencies performed a second calibration session. Measurements from the encoder (Degrees) and
optical fibre (Voltage) were acquired by means of the DAQ and a XY graph is displayed. The Labview program
includes a polynomial regression of the graph representing the angle (proportional to the shifting of the piston) in
function of the voltage of the optic sensor. The relationship between these data is nonlinear. Several tests were
necessary to conclude that the relation was a ninth order polynomial. Figure 21 shows the different polynomial
regression obtained during the testing. It is obvious that lower orders are not giving reliable polynomials (red
line): they are not close enough to the original points (white points). The 9th order give a 1degree precision
calibration.

Figure 21: Polynomial regressions for sensor calibration 3rd order to 9th order

The angle/voltage relationship of various sensors was evaluated, and only the best was kept for the final device.
Different defaults were detected thanks to this calibration. First, the sensor might not be symmetrical, and in this


19

case, a hysteresis curve appeared. The forth way and the back way of the piston are not identical, so the
intensity received by the sensor will be different depending on the direction of the displacement. On Figure 22
left we can clearly see two curves corresponding to these two directions. Thus for one voltage value delivered
by the sensor, two positions of the piston are possible.

Secondly, if the optical fibres and the mirror are not correctly oriented and spaced, when the piston is at its
minimum range, it may not correspond to the maximum light reflexion (Figure 22 right). The maximum of
intensity will be achieved for a position xmax>0 of the piston, this means that for a certain values of the optical
sensor, there are two positions possible, before and after xmax. If the sensor presents this property, it cannot be
used for the device because the voltage is not injectively transformable into a position of the piston.

xmax

Figure 22 : sensor calibration defects – positioning problem (left) and hysteresis (right)

Lastly, the voltage output must be different for every position of the piston even if the range is almost at its
maximum. If the sensitivity of the sensor is too low, there will be no difference between the positions of the
piston when its displacement is superior to a certain value xmin . This happens if the optical fibre is not sensitive
enough to be able to detect the reflected light when the mirror is too far (Figure 23).

Figure 23: Sensor calibration defect- lack of intensity

The program

The program provides the interface of command of the DAQ. It allows controlling the device: display a set of
stimuli, record the data from the sensor and draw graphs. The program is written in Labview, a programming
software of National Instrument compatible with the DAQ used. Labview displays two windows: on the bloc
diagram all automatic components of the box are represented and wired together (Figure 26). On the front
panel, charts are drawn, selected values are shown, and command buttons permit the user to control easily the
device (Figure 24). The front panel displays charts of the position and the speed of the piston, but also raw data
like the voltage output of the sensor and the square wave commanding the valves to control, in case any error
happens in the program. The file path and browser to the Excel file containing the stimulation bloc, and the
entitlement of the recording file is also possible. An array displays the excel file and an indicator shows the clock
counts so that the running of the bloc can be checked.


20

The program is composed of three sequences: the initialization, the stimulation bloc and the termination. The
program stops when the bloc designed has reached its end, but it can also be stopped manually for safety
reasons.

Figure 24: Front panel

• The fMRI program

The initialization of the program contains the synchronization to the fMRI scanner, the uploading of the excel file
commanding the bloc of stimuli, and also the creation of the data file. The scanner contains an internal clock
that determines the acquisition of the image. The device needs to be synchronized with the same clock to
assure that the cerebral activity imaged is due to the paintbrush strokes. For the fMRI machine, the TRs
(Repetition Times) are taken as reference clock. The MRI task is created by indicating to the DAQ the name of
the channel delivering the TRs and the nature of the signal. The data acquired during each stimulation is saved
into files created and named at this moment of the program. On the same time, an Excel file of .csv extension
(Comma Separated Values File), containing all information of the stimulation block is read and converted into an
array to be read inside the second sequence. It contains a determined series of integers 0, 1, 2 or 3
corresponding to a default state, speed 1, speed 2 and speed 3 respectively (Figures 25 & 26).

The second sequence contains the command of the valves, the data acquisition of the sensor but also the data
and graph recording into the selected files. Three while loops are running simultaneously with different periods.
The command and data from valves and the sensor are recorded at a high frequency (10ms) as “raw data” and
“graph”. These raw data are then read by the second loop and saved into the file in a less high frequency
(100ms). And the charts are displayed from the “graph values” with a frequency even slower (200ms). All of
these loop running simultaneously. This split of acquisition and recording in this sequence avoid any overload of
data, and consequent bug in the program. The speed of the valves is driven by the value encountered in the
array designing the bloc. For every tick of the clock, the following value of the array is read and the state of the
valve can change. The number of counts of the clock are taken as the index number of the array: only one value
is expressed, for the Nth click, the Nth row of the first column of the excel file is read.

Figure 25: states of the valves – 0, Default (left) and 1, Speed 1 (right)


21

The last sequence is the termination: the file recording the data is closed and the valves are brought to their
initial state. Indeed, the piston needs to be at its minimum range at the beginning of the stimulation so that the
sensor acquires negative voltages. It will give positive displacement thanks to the transformation: the calibration
was made using this protocol.

Figure 26: fMRI program

• The NIRS program

In a NIRS machine, there is no writing possible: this means that a signal cannot be output. The communication
with the device must be issued from the Labview program to the machine through a RS232 USB cable. This
cable carries ASCII data and orders them in one column, each row corresponding to the spectroscopic value at
a given time. The NIRS machine will keep scanning while the ASCII data transported via the RS 232 cable.
Another image will be acquired when the value of the ASCII data changes.

The counter previously used in the fMRI program is not external any more but internal. A square wave of defined
frequency is generated and the edges are counted, replacing the TR counts. For one block stimulation, different
ASCII values are sent: one for each state of the valves (0, 1, 2 or 3). This way, for each NIRS image will
correspond one state of the valves. Figure 27 represents the data sent and the corresponding state of the
valves. At the end of this bloc, two images are acquired: one for state1 (corresponding to the a values), the
other for state 0 (for the b values).

Figure 27: Correspondence between states of valves and state of valves

22

The program functioning with the NIRS machine is similar to the fMRI one. Indeed it is still divided in three
phases, first the initialization, then the control of the valves and recording of data, and last the termination
(Figure 28).

Here, during the first phase there is no initialization of the DAQ for the MRI channel; it only contains the creation
of the file and the uploading of the matrix block.

During the second phase, the valves are still controlled by square waves, but the reading of the matrix is not
synchronized with an external counter but with an internal, created by counting calling edges of a square wave
of frequency f= 1kHz and varying between -1 and 1. The number of counts increases if the current value is
positive and if the last value is different. To each state of the valves corresponds the same number of the state
(0, 1, 2 or 3) but read as an ASCII data. This ASCII data is then sent with the RS 232 cable to the NIRS
machine.

The termination of this program is identical to the fMRI program.

Figure 28: NIRS program


23

Results

Preliminary tests

Before using the device with an imaging technique, it has been tested on adults to settle witch version of
different pieces of the robot was the most adapted for its final use. The position and shape of the paintbrush
and the design of the cushion were decided after a series of tests carried out on two adults. Furthermore, a first
assessment of the patient’s sensation of social touch was also possible by varying the speed of the piston. The
device was placed on the inside of the arm of the tester. The tester tried different devices and he was asked to
answer some questions about its sensation.

• The cushion

The three different cushions made for the purpose of this device were tested. Questions were asked to the
tester about the comfort, and its easiness to use was also observed. Here is a summarizing chart containing all
observations. Table 1.

Table 1: Results for the cushion test
Cushion Thickness Width Position of Notch for
straps tubing

Small Small Bottom Yes

Cushion 1

Large Large Bottom No

Cushion 2

Small Small Lateral side Yes

Cushion 3

Concerning the width, there was no difference observed by the subject, both large and small are comfortable.
Yet, from the examiner’s point of view, a large width is preferable. Indeed, the tubing and the optic fibre are
quite stiff and tend to crook, moving the piston from its initial position.

The thickness of the cushion doesn’t matter to the patient. The only condition that has to be met concerns the
high of the paintbrush, i.e. the high of the cushion at the piston’s tip. If it is too high, the paintbrush has to be
placed lower on the piston tip.

The position of the straps on the pillow played a lot in the tester’s sensation. During stimulation with the cushion
number 3, subjects are disturbed by the feeling of jolts. The air flowing into the tubing creates a jerk of the
piston and as the straps are attached on the lateral sides of the pillow, its movement are felt to a greater extend.


24

Lastly, the notches for the tubing did not have any influence on the patient’s sensation but the tubes were not
better supported with this adaptation. A horizontal upper side holds better the tubes and the optic fibre in place.

• The paintbrush

Two parameters of the paintbrush tips were taken into account during this preliminary test: the high of the
paintbrush and its shape.

First the tester was asked to determine how he felt the contact of the paintbrush on his skin, for different
positions of the brush. Indeed, if the paintbrush is positioned high on the piston, its hairs will only touch slightly
the skin. On the contrary, if the paintbrush is placed lower, all hairs will be in contact with the skin and the
touching area will be broader. There will also be more pressure on the skin with this position of the brush.

Tester found that when the hairs touched slightly the skin (big high) (Figure 29) it was more comfortable and that
they could better feel the displacement and thus the speed of the brush.

Figure 29: Different touch intensity- light (left) and more intense (right)

Secondly, different shapes of paintbrush were tested, and it was asked if the sensation differs for each of them.
The paintbrushes proposed were either round and small, round and big, flat, or fan: the contact ranged from
narrow to broad. The main question was: does the shape of the brush matters in your perception of the
movement? The nature of the bristles was also different and the tester had to evaluate how pleasant the touch
was. Two brushes had nylon hairs, one had squirrel hairs, and a last one had polyester hairs. Figure 30.

The results concerning the shape of the brush were the followings: there was no difference felt in the sensation
of the displacement of the piston, no matter how broad the water brush is. The intensity of the response to the
stimuli seemed to be equal whatever the shape of the paintbrush. On the contrary, the softness of the bristles
mattered a lot. The polyester hairs are quite stiff and the stimulus is not pleasant.

Figure 30: Test of different shapes and softness of the paintbrush – big round, squirrel hairs (left), small round
acrylic hairs (centre) and fan plastic hairs (right)

• Speed

The preliminary test was also an opportunity to obtain some answers concerning the “social touch” feeling. Two
times, three different speeds were tested, corresponding to three different duty cycles on the square wave
controlling the valves, each α separated by 10 points. The values of the duty cycle were ranging from 70% to

25

95%, corresponding to velocities of 21mm/s to 3,5 mm/s respectively. The value of maximum velocity is
Vmax=70mm/s. To the question: which speed between the three was the most agreeable (++), testers answered
speed the medium velocity. Tester also agreed to say that the less pleasant touch (-) occurred for high
velocities. Results are shown in Table 2.

Table 2: Results for assessment of speed
Speed (mm/s) 3,5 7 10,5 14 17,5 21

Appreciation Adult 1 + + ++ + - -

Appreciation Adult 2 + ++ ++ ++ + -

The frequency was also modified a bit to test the smoothness of the displacement. For a frequency of 17hz, the
tester would feel less discontinuity in the paintbrushes’ velocity, for every duty cycle value. Yet a frequency of
17Hz does not work with a duty cycle of 95%, which is why for this value of α only frequencies below 15Hz
were tested.

fMRI test on adult

The recording of a subject in the MRI scanner studies the brain activation while feeling the paintbrush strokes on
the forearm. The study of the somatosensory homunculus of an adult brain allows us to predict the cortical
areas activated by this sensory stimulus (Figure 31). According to this functional topography, passive touch
sensitivity on the forearm is expected to cause a response on the top of the somatosensory cortical strip.
However, we did not have a definite hypothesis as to whether activity associated to the touch sensitivity would
be observed contra-laterally or bilaterally.

Figure 31: functional topography of brain

The device was first positioned inside the fMRI machine to be certain it was MR proofed. The device has then
been tested on a healthy male adult subject using a Philips 3Tesla MRI scanner.

This recording was constituted of two block events. Each paradigm lasted 256 TRs with a TR of 1.5s, which
equalled 6mins and 24sec. During a block event, the paintbrush would alternate back and forth movements at a
definite frequency during 16TRs, and rest periods of 16TRs. Two frequencies were tested: 2Hz and 3Hz.
Results are shown in Figure 32 and 33. For both paradigms, the functional activity is found in the primary
somatosensory cortex, close to the top, corresponding to the forearm. On the transversal section, we can see a
deeper bilateral activation.


26

Besides on the time series statistics (Figure 34), the synchronization between the brain activation and the brush
[xxx?] actuation can be seen, proof of the stimulus creating by the device.

Figure 32:fMRI image for a 2Hz stimulus

Figure 33: fMRI image for a 3Hz stimulus

Figure 34: Timeseries statistics during the block paradigm
:
Comparison between the stimuli and the cortical
response

Safety Measures

• Hardware

The different parts of the device were built to insure the maximum of safety during its use. First, the piston is
safe to use on infants because its extension is limited and small and it is very light. Indeed, the piston is made in
plastic and the movement of the paintbrush is limited to a back and forth shift of 15mm. Secondly, the
paintbrush has been chosen to be soft enough to avoid any irritation to the baby. The device holds on the
baby’s limb with adjustable straps and, thus in case of emergency, it is easy to remove the device from the
infant. The soft side of the strap is in contact with the skin to avoid any irritation. Finally, all parts of the device
are fitted into one another and not glued: it is easy to remove any part of the device if necessary.

Two valves and their regulator control the shift of the piston. The regulator helps controlling the input pressure of
the air coming into the valves, so that shift of the valves is not too violent and safe. The valves are also protected
for any electrical damage thanks to a fuse incorporated on the strip board. Furthermore, it is possible to stop
the valves easily with the switch commanding the power supply to the valves. At last, in case of emergency, an
emergency button has been added to the control box to ease the complete stop of the device.

• Software


27

Two main safety measures of the software control the functioning of the device. First, several graphs display the
input signal of the valves, and the voltage from the sensor, thus it is easy to detect any defect during the
functioning of the device.

Moreover, the program stops when the bloc designed has reached its end, but it can also be stopped manually
for safety reasons.


28

Discussion

Choice of equipment

• The piston

The piston used in this project has very small dimensions. Its lightweight and small thickness are strong
advantages to use with babies. Yet the short range of the piston may be an inconvenient because the
paintbrush stroke will not be long. Thus the stimulation could last longer and may be perceived differently by the
patient. In the literature the surface of skin brushed has not been specified, consequently no comparison can be
made. With a bigger piston, a test about the reaction of the patient for different stroke length could be
implemented.

One issue concerning the movement of the piston rose during the conception of the device: the tip holding the
paintbrush must not turn laterally. Yet a piston always rotates, especially when it meets a resistance: the skin in
our case. The problem was solved by using in parallel another tube-rod system (the sensor), thus leaving only
one degree of freedom.

• The sensor

The most difficult part of the construction of the device was the sensor. The final sensor is acceptable as
precise (to 1/10mm) and reliable data are obtained, but an improvement on its size could be made. The system
used here is simply based on the reflexion on a mirror and the light propagation in two optical fibres: it is an
easy way to measure linear displacements. Any other position sensor, or even a speed sensor can be used, as
the velocity of the piston is the most important value to be measured in this project. The main drawback of the
system used is it volume. It doubles the size of the device and the optic fibres coming out the piston tend to
lean it away from its initial position.

Imaging techniques

Both methods use changes in blood flow to study neuronal activity but for several reasons, NIRS is preferred for
this project. Functional MRI has proven to be very successful in studies where adults use free viewing, providing
opportunities of comparisons across tasks. Yet, fMRI is not easy to apply with infants as children tend to move
when they are awake, thus increasing the probability of motion artefacts. A solution to that is to scan the child
while sleeping, but this involves only a passive state, that might not be compatible with the experiment. With
NIRS, the child is sitting and allowed to move slightly, thus helping the image acquisition. Finally, NIRS measures
not only deoxygenated blood flow (like fMRI), but also oxygenated blood flow with a high signal-to-noise ratio.
Studies have proven that due to this limited information, fMRI did not give correct brain activity characteristics in
some parts of the infant’s cortex.

One disadvantage of NIRS is usually scatter due to the skull and hair, but as infants tend to have fine hair and
thin skulls, the signal loss is less than for adult participants. The last limitation concerning NIRS is that the
measurement is only possible near the cortical surface, approximately 5cm deep. For the small head of
toddlers, 5cm is deep enough to visualize the activity of the selected part of the brain. [14] Cerebral activity
outside this region cannot be imaged unless the probes are moved. Yet, with the NIRS machine of the Babylab,
specially designed for babies, there are a limited number of electrodes to lighten it. And there is precisely no
electrode in the primary sensory cortex zone, where the region relative to touch is situated. Thus it might not
possible to visualize the whole cortical response to social touch stimuli.


29

Conclusion

The aim of this project was to develop a simple device stimulating sensitivity to touch of infants at risk of autism,
to be used with fMRI or NIRS for recording brain activity. The requirements for this device were that it had to
reproduce social touch, be controllable in velocity, fMRI compatible and reproducible.

The device was successfully designed and enables to control the touch stimuli remotely. The device is small
enough to fit on an infant’s limb, and the stimulation can be easily synchronised with both fMRI and NIRS
machines. The device is safe provided the user is alert on its functioning. Moreover the device was proven to
stimulate tactile activation on an adult subject, suggesting that activation could be similarly achieved with
babies.

Though further technical improvements could be made, the prototype developed will enable experiments with
infants and it is to hope that it will bring new clues on sensing mechanisms in autistic children.

We hope that, in the future, the findings and technology provided by this robotic system could be employed to
perform an early diagnosis of autistic disorders and, perhaps, to devise early intervention methods that could
improve clinical outcome.


30

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