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ORIGINAL ARTICLE
Odour detection in children and young people with profound
intellectual and multiple disabilities
Geneviève Petitpierre | Juliane Dind | Catherine De Blasio | Germaine Gremaud
Department of Special Education, University
of Fribourg, Fribourg, Switzerland
Correspondence
Geneviève Petitpierre, Département de
Pédagogie Spécialisée, Université de Fribourg,
R. St Pierre Canisius 21, CH-1700 Fribourg,
Switzerland.
Email: genevieve.petitpierre@unifr.ch
Funding information
Givaudan Foundation; Stiftung
Heilpädagogisches Zentrum [Special needs
educational Foundation]
Abstract
Background: Olfaction provides information on very important dimensions of the
environment; however the olfactory abilities of children and young people with
profound intellectual and multiple disabilities (PIMD) remain largely unknown.
This within-subjects study explores olfactory detection abilities in children
with PIMD.
Method: Twenty-two children and young people with PIMD (7–18 years) were pres-
ented with 18 medium intensity odours and an odourless control stimulus. Odorants
were presented one by one in a randomised order. The neutral stimulus was pres-
ented prior to each odorant. Participants' responses were measured using 21 behav-
ioural indicators.
Results: Results show that participants make a clear distinction between odorous
and neutral conditions, between food and non-food, and between pleasant and
unpleasant odours. The detection abilities are manifested by several behaviours, in
particular by the duration of the head alignment on the odorant.
Conclusions: This study shows that participants detect the stimuli and act differently
depending on the category.
KEYWORDS
odour, olfaction, profound intellectual and multiple disabilities, sensory behaviour
1|INTRODUCTION
Since most persons with profound intellectual and multiple disabil-
ities are also hindered by visual and/or auditory impairments, the
olfactory function, if intact, can be a useful compensatory tool to
strengthen interactions between these people and their environ-
ment. This sensory modality provides information on essential
dimensions of physical and social contexts (Schaal et al., 2020;
Stevenson, 2010). Observations about olfactory functioning in peo-
ple with PIMD are nevertheless anecdotal. Roemer et al. (2018)
found that people with PIMD use the sense of smell least of all the
senses. An explanation for the lack of studies on olfaction in people
with PIMD lies in the fact that conducting experimental studies
involving this population is very challenging (Maes et al., 2021).
People with PIMD form a heterogeneousgroupintermsoftheori-
gin of the disability (Nakken & Vlaskamp, 2007). Their participation
is strongly impacted by profound or severe intellectual impairments
combined with profound or severe motor disorders. They often
have to deal with complex medical conditions and present frequent
sensory impairments, especially visual and auditive (Dorche, 2021;
Jacquier, 2021; van Blarikom et al., 2009). Understanding and
communicating with them is often difficult as they mainly, if not
exclusively, express in non-, proto- or pre-verbal ways, or via
idiosyncratic communicative behaviours.
Received: 22 June 2021 Revised: 10 November 2021 Accepted: 14 November 2021
DOI: 10.1111/jar.12963
Published for the British Institute of Learning Disabilities
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any
medium, provided the original work is properly cited and is not used for commercial purposes.
© 2021 The Authors. Journal of Applied Research in Intellectual Disabilities published by John Wiley & Sons Ltd.
J Appl Res Intellect Disabil. 2021;1–12. wileyonlinelibrary.com/journal/jar 1
Knowledge available for other populations with neurodevelop-
mental disorders is not helpful as it remains ‘close to nothing’
(Dan, 2019). Atypical olfactory processing or morphological atypicities
have been indicated in a few syndromes (Lyons Warren et al., 2021;
Manan & Yahya, 2021; Sarnat & Flores-Sarnat, 2017, 2019) but,
except for autism spectrum disorders (Crow et al., 2020; Tonacci
et al., 2017 for reviews), data are scarce and not conclusive. In people
with cerebral palsy, no relationship was found between olfactory and
gross motor functions (Nakashima et al. 2019).
With respect to evaluation, olfactive standardised tests, which
are attentionally, verbally and cognitively demanding, can only be
administered from 3 to 4 years of developmental age (Cameron,
2018). Hetero-evaluation could be used to explore the perceptive
abilities of people with PIMD; however this is an indirect procedure,
which may reduce the quality of the observations reported (Todorov
& Kirchner, 2000). Notwithstanding its cost and high degree of techni-
cality, psychophysical assessment offers the advantage of a direct and
rigorous measurement. Commonly used to observe infants' olfactory
functioning, this procedure can be used beneficially in pre- or non-
symbolic populations difficult to study by other means.
With respect to intervention, the development of olfaction is
rarely mentioned as an objective in personalised educational programs
for people with PIMD (Petitpierre et al., 2017). Some incentives to
use odours with this population do already exist to prevent sensory
deprivation or boost cognitive functioning (Fröhlich, 2000; Govern-
ment of Ireland, 2006; Haute Autorité de Santé, 2020; Hulsegge &
Verheul, 1987). Olfactory stimuli are also used in multi-sensory books
as a ‘safe’alternative choice when the direct support persons are not
sure or lack prior knowledge about a person's tactile preferences or
abilities (Ten Brug et al., 2012). However olfactory stimulation in daily
care is currently only empirical. The support workers do not have
guidelines to observe and interpret the responses manifested by peo-
ple with PIMD, and their intervention usually takes place without any
evidence, which is not very satisfactory. Educational staff report that
olfactory functioning is one of the sensory dimensions for which they
need more knowledge (Vlaskamp et al., 2007).
The present study has been developed at the request of a special
needs education school for children and young people with PIMD.
This school has used olfactory stimulation for several years and was
wondering how to scientifically investigate how children and young
people with PIMD respond to odours. The two following research
questions were formulated in collaboration with the school: do chil-
dren and young people with PIMD behave differently in the presence
of an olfactory versus a neutral stimulus, and what detection behav-
iours do they exhibit? Because of the scarcity of studies on the topic,
the hypothesis corresponding to the first question was formulated on
a bilateral basis, that is, children and young people with PIMD were
expected to behave differently in the presence of an olfactory versus
a neutral stimulus, regardless of the direction of the difference. More-
over, since factors such as gender, age, mood, medication, as well as
olfactory environment are likely to moderate odour detection and per-
ception, exploratory analyses targeting the role of some observed, not
manipulated, individual factors were also conducted.
2|METHODS
2.1 |Procedure
This within-subjects study has been authorised by the Geneva and
Vaud ethics committees (ID: 2019-00234), which are part of the
national organisation Swiss ethics. Written consent was obtained
from parents or legal guardians before the start of the study. The
researchers committed to postpone the session if the child's state
of alertness, fatigue or health required it and to permanently dis-
continue a participant's participation if they showed discomfort
after two sessions of odour exposure. A pilot study preceded the
experimental study in accordance with the recommendations of
Maes et al. (2021).
2.2 |Participants
The participants were recruited in three Swiss French-speaking special
education schools. The referent teacher or support worker were
asked to select participants meeting the three following criteria: (1)
presenting the key characteristics described by Nakken and
Vlaskamp (2007); (2) be aged between 7 and 18 years; (3) have
attended the school for at least 6 months at the time of the recruit-
ment. Children presenting food allergies or chronic airway problems
with indication of daily respiratory therapy were excluded. Twenty-
five children and young people met the criteria and were included in
the convenience sample of the study. Three children left the study at
the very beginning of data collection, two because of severe health
problems, the third because he could not stand the experimental set-
ting. The final sample of the study includes 22 participants aged
between 7 and 18 years (M=13.0 years; SD =3.4), all attending a
special educational school program. Demographic data (age of the
child, gender, aetiology [if known], comorbidities, motor and commu-
nicative abilities) was collected from participants' clinical files by their
teachers and support workers. Participants were also assessed
through the French validated version of the Mood, Interest and Plea-
sure Questionnaire [MIPQ] (Ross & Oliver, 2003; Verbel Sierra, 2013),
and through questionnaires on gastroesophageal reflux and nausea
responses (Senez, 2013a, 2013b). Participants' characteristics are
shown in Table 1.
2.3 |Stimuli
A total of 19 olfactory stimuli (18 odorous and 1 odourless solvent as
control stimulus) were used (Table 2). Ten odorants were food odours
(basil, orange*, Nutella, green vegetables, rancid butter, cinnamon,
cheese, strawberry, apple pie and garlic*), eight were non-food odours
(chlorinated swimming pool water, pony, summer rain, rose*, lily of
the valley, grass*, hand sanitizer [Sterilium
®
]** and sweat). Stimuli
were selected in collaboration with the school that initiated the
research. Odours that might be present in the context of everyday life
2PETITPIERRE ET AL.
Published for the British Institute of Learning Disabilities
were preferred. The stimulus set corresponds to six of the eight cate-
gories of the typology identified by Castro et al. (2013). Four stimuli
marked with a single asterisk (*) come from the ‘Sniffin' Sticks test’,a
standardised worldwide-used test manufactured by Burghart
Messtechnik GmbH [http://burghart-mt.de/en/]). One odour, marked
with the double asterisk (**), comes from a commercially available
product. The other 13 stimuli were created on request by the Swiss
perfume and aroma company Givaudan SA. All ingredients used in the
production of the stimuli meet the Swiss standards in terms of regula-
tion on cosmetic products (OCos of 16 December 2016; ODAIOUs of
16 December 2016). The calibration of the intensity of the stimuli cre-
ated for the study required a three-step procedure. In the first step,
eight members of the steering group (two researchers, three represen-
tatives of the school that initiated the research and three representa-
tives of the funding foundation), assessed the intensity of a first set of
stimuli using a Likert scale ranging from 1 (no odour at all) to 9
(extremely strong odour). The concentration of some stimuli was
adapted to reach an average perceived intensity. The stimuli were
then tested for intensity by 29 adult volunteers working in the
Givaudan company. All odours reached an intensity range of 4.5–6.5
(neither too strong nor too weak), except summer rain and pool water.
We nevertheless decided to keep these two odours in the panel
because the intensity range was not excessively small. For the weak-
est odour (pool water), we discarded the idea of increasing the pro-
portion of chlorine in the water beyond the proportion usually used in
swimming pools for safety reasons. The volunteers were also asked to
identify the stimuli and to categorise them hedonically into three cate-
gories (pleasant, unpleasant, neither pleasant nor unpleasant). As they
usually rate odorants as being more intense and more pleasant than
adults (Bensafi et al., 2007), it would have been better if children, not
adults, had performed this pre-categorisation. However cross-cultural
judgements about bad smells are highly convergent (Schaal et al.,
1998) even from an early age (Wagner et al., 2013), probably because
bad odours have an alarm function and too much variability under the
effect of environmental factors would put the individual at risk
(Bensafi & Rouby, 2021). For good odours, variability is usually
greater (Ferdenzi et al., 2011). In our sample, only four children out of
22 are of non-European origin; the other 18 are European through at
TABLE 1 Participants' characteristics
Demographics (%)
Gender
Male 14 (36)
Female 8 (64)
Aetiology
Cerebral palsy 5 (23)
Syndromic aetiology 6 (27)
Within degenerative syndrome (n=1)
Cerebral palsy and syndromic aetiology 1 (4.5)
Other 10 (45.5)
Epilepsy
Seizures controlled by medication 11 (50)
Seizures once a month 2 (9)
Seizures once a week 2 (9)
Seizures once a day 1 (4.5)
Several seizures a day 1 (4.5)
No epilepsy 5 (23)
Visual impairment
Confirmed 17 (77.5)
Presumed 1 (4.5)
No visual impairment 4 (18)
Auditive impairment
Confirmed 1 (4.5)
Presumed 2 (9)
No auditive impairment 18 (82)
Missing 1 (4.5)
Tactile impairment
Confirmed 7 (32)
Presumed 6 (27)
No tactile impairment 9 (41)
Vulnerability to hypernausea reflex
a
Often 9 (41)
Sometimes 12 (54.5)
Rare/not observed –
Missing 1 (4.5)
Vulnerability to gastroesophageal reflux
Often 3 (14)
Sometimes 17 (77)
Rare/not observed 1 (4.5)
Missing 1 (4.5)
Feeding mode
Blended food 8 (37)
Chunky food 3 (13)
Enteral feeding (partial) 10 (45.5)
Enteral feeding (complete) 1 (4.5)
Medication
Medicated 21 (95.5)
Non-medicated 1 (4.5)
(Continues)
TABLE 1 (Continued)
Demographics (%)
Interest score
Low score (score between 0 and 17) 7 (32)
High score (score between 18 and 28) 15 (68)
Positive mood
Low score (score between 0 and 22) 9 (41)
High score (score between 23 and 36) 13 (59)
Negative mood
Low score (score between 0 and 17) 20 (91)
High score (score between 18 and 28) 2 (9)
a
No response for one participant with enteral feeding.
PETITPIERRE ET AL.3
Published for the British Institute of Learning Disabilities
least one of the two parents, including eight Swiss children, which
suggests a partially common ‘olfactory niche’(Bensafi & Rouby,
2021). As we know that prior experience can affect olfactory
responses (Martinec Nováková et al., 2018), the participants' parents
or legal guardians were asked to rate the familiarity of each odour on
a binary scale (0 =unfamiliar or not familiar at all; 1 =somewhat
familiar or very familiar). Unfortunately, we only received the
responses of 15 families out of 22. Given this low response rate, we
decided not to use this information as a moderator in the analyses.
Odours were dispensed in Burghart pen-like devices 14 cm long and
1.3 cm diameter. These devices were chosen for their very hermetic
closing mode which limits ambient olfactory ‘contamination’and
makes them reusable. During the odour presentation, a protective tip
was added to the head of the stick in order to prevent the child's skin
or eye from coming into contact with the soaked wick.
2.4 |Measures
The Mood, Interest and Pleasure Questionnaire (MIPQ, Ross &
Oliver, 2003; Petry et al., 2010) is a 23-item Likert questionnaire with
three subscales: positive mood (nine items, max. 36 pts), negative
mood (seven items, max. 28 pts) and interest and pleasure scale
(seven items, max. 28 pts). Internal consistency of the French version
(Verbel Sierra, 2013) is good (Cronbach's alpha =.97 for the total
scale; Pearson r=.90 for interrater reliability). The total score of the
test is a maximum of 92 points. High scores denote high mood and
interest and pleasure levels.
The gastroesophageal reflux disease observation form is a 19-item
Likert questionnaire (Senez, 2013a). Items are scored on a 3-point scale
(no problem; some problems; significant problems). The total score
ranges between 19 (no signs) and 57 (all signs present). The Nausea
responses observation form is a 10-item Likert questionnaire (Senez,
2013b). Items are scored on a 3-point scale (often; sometimes; never).
The total score ranges between 1 (no signs) and 30 (all signs present).
These two questionnaires are clinically recognised by speech therapists
in France, but have never been scientifically validated.
2.5 |Procedure
The experiment was performed in the participants' schools. Rooms
were chosen for their quietness and good ventilation. All participants
were sitting in their own seats during the presentation of the odor-
ants. Postural adaptations (such as headrest or support behind the
neck if needed by participants to allow maximum mobility) were dis-
cussed with the children's physio- or occupational therapists and
tested before the experiment. A tripod with an articulated arm and a
clip was used to bring the stimulus close to the participant's nose. The
device was used to prevent the researcher from bringing his or her
arm or hand too close to the child's face, which might have prompted
the child to respond to the speaker's proximity, rather than to the
odour. The device also aims to prevent the adult's hand from hiding
the child's face and to prevent olfactory interference with the
researcher's body odours.
Three people (two researchers and a direct support person) were
present in the room during the sessions. Researcher 1 stood to the right
or left of the child while presenting the stimuli. His or her position was
switched from one session to another to avoid participant orientation
bias. Cotton gloves were used to handle the sticks. Researcher 2 was in
charge of time indications and made sure that the cameras were working
properly. The third person was the child's teacher or educator. He or she
was in charge of interrupting the session if the participant showed any
reaction of discomfort, according to the ethical commitments made by
the researchers. They were also systematically asked if the child was in a
stable behavioural and/or health condition for the experiment. When
presenting the stimuli, Researcher 1 opened the stick, fixed it on the clip,
presented it about 2 cm from the participant's nose, between nose and
chin (cf. Lima et al., 2011). To reduce the risk of fatigue and olfactory
adaptation (i.e., temporary decrease in olfactory sensitivity following
stimulation, Köster & de Wijk, 1991), the experiment was conducted in
three sessions spaced about 1 week apart, during which a randomised
sequence of six odorants and six neutral stimuli were presented. Odor-
ants were presented successively in a randomised order (Hasard
®
soft-
ware) for 15 s. In order to enable sufficient recovery of the sense of
smell, the inter-odorant neutral stimulus duration was 30 s, during which
only the last 15 s were coded, except for two indicators to observe the
participant's reaction 2 and 5 s, respectively, after the introduction of
the stimulus. No words were addressed to the participant during the
sequence. The total assessment time: 18 odorous stimuli * 15 s and 18
odourless stimuli * 30 s, was 13.5 min per participant.
The sessions were videotaped by two digital camcorders placed
in front of the participant. One was focused on the participant's face,
the other on his or her body. See Petitpierre & Dind (under review)
for a detailed presentation of the procedure.
2.6 |Coding
Twenty-one behavioural indicators were used to code the behaviours
exhibited by the participants, of which 14 were coded on duration (milli-
seconds)andsevenonoccurrences.Thegridwasatwo-levelone.It
specifies the operational definition of the indicator as well as behaviours
that should not be coded (first level). The operational definition was
sometimes accompanied by a video illustrating both the targeted or
excluded behaviours. If necessary, it provides additional information for
participants who express themselves in an idiosyncratic way (second
level). The grid is presented in Appendix 1. We chose to code some
behaviours on duration and others on occurrences and based our deci-
sion on methodological knowledge (i.e., Thompson et al., 2000), on new-
borns and young infants olfaction research (Schaal et al., 1998, 2002),
and on the results of the pilot study. Two criteria have been considered:
(1) the relevance and (2) the simplicity of the method of measurement
for the target behaviour. Occurrence recording involves recording the
number of times the target behaviour is observed to occur during a
pre-defined observation period. It makes sense for shortly manifested
4PETITPIERRE ET AL.
Published for the British Institute of Learning Disabilities
behaviours (‘sniffing’,‘yawning’,‘pouting’,‘nausea reaction’,‘rejecting
the odorant’,‘moving the head towards the stick’, etc.), but is not useful
for behaviours that are not easy to count (e.g., maintaining a posture, in
our case ‘head alignment on the stick’;‘showing stereotypies’and ‘being
physically active’;‘holds the stick by coordinating hand, nose, etc.’), nor
for behaviours that occur very infrequently (e.g., ‘emotional outburst’).
Duration recording involves recording the time that elapses between the
moment when the target behaviour begins and when it ends. It makes
sense for actions that involve a number of steps (e.g., in our case ‘explor-
ing with one's mouth’) or when the frequency of the behaviour is very
rare (e.g.. ‘emotional outburst’). For simplicity, we have also coded the
duration for behaviours that the participant exhibits repeatedly, as long
as the interval between two manifestations of the behaviour is not
greater than 1 s (e.g., ‘positive/negative/non-interpretable vocalisations’,
‘grinding’,‘chewing’,‘moving one's lips’). The most difficult decision con-
cerned the coding of smiles. Finally, we chose to measure the duration
of the smile, which allows us to make statements about the percentage
of time a person spends smiling while exposed to the odour or the neu-
tral stimulus. In any case, either occurrence or duration recording
requires very precise behavioural definitions; that is why we have
included temporal specifications in the operational description of some
of our behaviours. For the analyses, only raw values (occurrences and
durations) were used.
The coding was carried out by a team of three coders. Two of
them have a doctoral degree in special education, the third a MA
degree. All coders were experienced in video analysis, two of them
with the target group. Two coders were also experimenters. During
the experiment, the stimuli and the neutral stimulus were designated
by a number. The coders who were not experimenters were blind to
the nature of the odorant, except for the neutral stimulus, whose
more frequent presentation could be a potential cue. When the coder
was one of the experimenters, we cannot exclude that he or she
remembered the association between the number and the type of
odorant. The coding was done both in continuous and real-time mea-
surement. The coding procedure was set up in the EUDICO Linguistic
Annotator [ELAN]) Software version 5.9 (Max Planck Institute for Psy-
cholinguistics, Nijmegen, The Netherlands). A refined reliability assess-
ment procedure using EasyDIAg algorithm (Holle & Rein, 2015) was
used to check both the observers' agreement about presence/absence
of a behaviour and the temporal overlap of their coding. The reliability
value (kappa) was calculated on 20% of the data. The accuracy of the
grid makes it possible to reach a satisfactory interobserver agreement
for 13 indicators: head alignment on the stick (k=.83); sniffing
(k=.55); chewing (k=.89); moving the lips or tongue (k=.62); smil-
ing (k=.72); pouting (k=.77); yawning (k=1.00); moving the hand
or head towards the stick (k=.81); rejecting the stick (k=.85); being
TABLE 2 Characteristics of stimuli
Perceived intensity Familiarity
a
Stimuli Food/non-food Hedonicity M(min.–max.) SD MSD Classification
b
Orange (Burghart) F P 5.00 (2–6) 0.92 0.48 0.48 C1
Nutella F P 5.82 (4–7) 0.61 0.48 0.51 C7
Cinnamon F P 6.10 (5–9) 0.93 0.29 0.46 C7
Strawberry F P 6.00 (4–7) 0.80 0.62 0.49 C5
Cheese F U 5.07 (2–8) 1.33 0.81 0.40 C8
Garlic (Burghart) F U 6.45 (5–9) 0.91 0.38 0.49 C8
Green vegetables F N 5.85 (3–9) 1.13 0.86 0.35 C6
Rancid butter F N 5.52 (3–8) 1.09 0.05 0.22 C8
Apple pie F N 5.90 (4–8) 0.90 0.48 0.51 C7
Basil F N 6.04 (4–8) 0.92 0.38 0.49 C4
Lily of the valley NF P 5.36 (4–9) 1.02 0.13 0.35 C4
Summer rain NF P 3.59 (2–5) 0.93 0.48 0.51 C6
Rose (Burghart) NF P 5.68 (4–8) 0.81 0.20 0.41 C4
Hand sanitizer (Sterilium
®
) NF U 5.21 (2–8) 1.17 0.52 0.51 C2
Sweat NF U 5.66 (2–8) 1.44 0.33 0.48 C8
Swimming pool NF N 2.80 (1–6) 1.21 0.70 0.47 C2
Pony NF N 5.38 (4–7) 0.98 0.14 0.35 C8
Grass (Burghart) NF N 5.62 (1–8) 1.26 0.52 0.51 C6
Neutral NF – – ––––
Abbreviations: C1, citruses, and so on; C2, disinfectants, alcohol, chemical, and so on; C3, mint, camphor, and so on (not presented); C4, flowers, plants,
aromatics, and so on; C5, fruits except citruses, and so on; C6, leaves, wood, grass, and so on; C7, Honey, nuts, bakery, and so on; C8, Apple, acid, putrid
rancid, garlic, and so on; N, neither pleasant, nor unpleasant; P, pleasant; U, unpleasant.
a
Available for 68% of the sample only.
b
Categorical membership of the stimuli in Castro et al. (2013) two-dimensional embedding of the descriptor-space.
PETITPIERRE ET AL.5
Published for the British Institute of Learning Disabilities
physically active (k=.74); making positive vocalisations (k=.80);
uninterpretable vocalisations (k=.44); all vocalisations (k=.68). Due
to insufficient data in the random selected files, the interobserver
coefficient could not be calculated for eight indicators. A total of 792
files (22 participants * 18 odorous +18 neutrals) coded on 21 indica-
tors results in a total of 8170 observations. The average number of
observations per participant was 371.
2.7 |Analyses
As the data were not normally distributed, non-parametric statistics
have been used to perform the analyses. Data for odorous versus
neutral, food versus non-food, pleasant versus unpleasant conditions,
was analysed with Wilcoxon signed rank test (Z), alpha level at .05
(bilateral). Effect sizes for Wilcoxon were calculated according to Pal-
lant (2020), that is, by dividing the test statistic by the square root of
the number of observations. Generalised linear mixed models (t) were
used to explore the role of personal characteristics on the olfactive
response. All analyses were performed using SPSS software version
26.0.0 (IBM Corp.).
3|RESULTS
3.1 |Response to odorous versus neutral
condition
The first analysis aims to study whether participants responded differ-
ently to odour versus neutral condition. To test this hypothesis, the
TABLE 3 Participants' behaviour in the odorous versus neutral condition
Odorous versus neutral condition Wilcoxon S-R test Effect size
Variables
Positive
ranks
A
(N)
Sum of
ranks
Negative
ranks
B
(N)
Sum of
ranks
Ties
C
(N)Z
p
bilateral
reta
squared
a
Nose/head
Head alignment on the stick 21 252 1 1 0 4.07
D
.000 .614
A
Nose/hand on the stick 7 28 0 0 15 2.36
D
.018 .356
A
Sniffing 14 131.50 2 4.50 6 3.29
D
.001 .496
A
Mouth
Exploring with one's mouth 6 26.50 1 1.50 15 2.12
D
.034 .320
A
Grinding (teeth) 1 1 1 2 20 .447
C
.655
Chewing 11 81 2 10 9 .2.48
D
.013 .374
A
Moving one's lips/tongue 14 178 8 75 0 1.67
D
.095
Nausea reaction 4 10 0 0 18 1.84
D
.066
Emotion
Smiling 13 166 8 65 1 1.75
D
.079
Pouting, making a face 16 176 3 14 3 3.26
D
.001 .491
A
Yawning 0 0 7 28 15 2.37
C
.018 .357
B
Emotional outburst 1 1 0 0 21 1.00
D
.317
Hands/arms
Moving hand/head towards
the stick
16 183 3 7 3 3.54
D
.000 .534
A
Rejecting the stick 15 120 0 0 7 3.42
D
.001 .516
A
Body
Interrupting motor action 4 13 1 2 17 1.49
D
.136
Being physically active 8 87 14 166 0 1.28
C
.200
Showing stereotypies 1 1 1 2 20 .447
C
.655
Vocalisations
Positive 9 63 4 28 9 1.22
D
.221
Negative 6 42 8 63 8 .655
C
.510
Uninterpretable 7 55 11 116 4 1.32
C
.184
All vocalisations 11 101 9 109 2 .149
C
.881
Note: Bold values denote statistical significance at the p< 0.05 level; A, Odorous condition > Neutral condition; B, Odorous condition < Neutral condition;
C, Based on positive ranks; D, Based on negative ranks.
a
The effect size (r) was calculated from Pallant (2020).
6PETITPIERRE ET AL.
Published for the British Institute of Learning Disabilities
data has been aggregated for all odorants and all neutral stimuli,
respectively, and compared to one another for each indicator. The
results show that participants respond significantly differently to the
odour condition compared to the neutral. A difference is present in 9
of the 21 indicators (Table 3). The effect size, calculated according to
Pallant (2020), is large or nearly large in four indicators. The head
alignment on the stick is significantly longer in the odorous condition
(Mdn
Odours
=6.69 vs. Mdn
Neutrals
=4.34 s; Z=4.07, p=.000). The
number of hand or head movements towards the stick is significantly
higher in the odorous condition (Mdn
Odours
=.81 vs. Mdn
Neutrals
=.42
occurrences; Z=3.54, p=.000), as well as the number of stick
rejection behaviours (Mdn
Odours
=.06 vs. Mdn
Neutrals
=0 occurrences;
Z=3.42, p=.001) and the number of sniffing behaviours (Mdn
Odours
=.17 vs. Mdn
Neutrals
=0 occurrences; Z=3.29, p=.001). The effect
size is nearly large for pouting with four times more pouts in the odorous
condition compared to the neutral (Mdn
Odours
=.22 vs. Mdn
Neutrals
=.055 occurrences; Z=3.26, p=.001) and moderate for nose/hand
coordination on the stick (Z=2.36, p=.018), chewing (Z=2.48,
p=.013), exploring the stimulus with the mouth (Z=2.12, p=.034),
which appear significantly longer in the odorant condition than in the
neutral condition. Conversely, the number of yawning occurrences is
higher in the neutral condition (Z=2.37, p=.018).
3.2 |Response to food versus non-food odorants
The second analysis aims to study whether participants responded
differently to food versus non-food odorants. Results indicate that
participants sniff the edible odorants more than the inedible ones
(Z=2.46, p=.014, r=.37) and they coordinate their nose and
hand on the stick more often (Z=2.19, p=.028, r=.33). Chewing
is only tendential (Z=1.78, p=.075, r=.27).
With regard to food versus neutral stimuli, a significant effect was
observed in 9 of the 21 indicators (see online Supplement 1 for details).
The effect size was large (r> .50) for one indicator (head alignment on
the stick). It was moderate (rbetween .30 and .49) for six (nose/hand
FIGURE 1 (a) Feeding mode on hand/head movements. (b) Interest score on nose/head alignment. (c) Positive mood score on hand/head
movements. (d) Positive mood score on nose/head alignment
PETITPIERRE ET AL.7
Published for the British Institute of Learning Disabilities
coordination on the stick; chewing; pouting; moving hand or head
towards the stick; rejecting the stick; sniffing) which prevail in the
edible odorant condition versus neutral while two (yawning; being
physically active) prevail in the neutral compared to the edible. The
effect of non-food odorants versus neutrals was observed in 8 indi-
cators out of 21 (see online Supplement 2 for details). Two indicators
(head alignment on the stick; moving hand or head towards the stick)
show large effect sizes (r> .50). Effect sizes were moderate
(rbetween .30 and .49) for the other six (nose/hand coordination on
the stick; exploring the stimulus with the mouth; pouting; rejecting
the stick; smiling; sniffing), which were all more prevalent in the
presence of the odorant.
TABLE 4 Significantly manifested behaviours according to the type of stimuli
All stimuli Food versus non-food Pleasant versus unpleasant
Scented
versus
neutral
Food versus
neutral
Non-food
versus neutral
Food versus
non-food
Pleasant
versus neutral
Unpleasant
versus neutral
Pleasant versus
unpleasant
Nose/head
Head alignment
on the stick
S>N F>N NF>N P>N u>n
Nose/hand on the
stick
s > n f > n nf > n f > nf
Sniffing S > N f > n nf > n f > nf p > n
Mouth
Exploring with
one's mouth
s>n nf>n p>u
Grinding (teeth)
Chewing s > n f > n
Moving one's lips/
tongue
u>n
Nausea reaction
Emotion
Smiling nf > n p > n
Pouting, making a
face
s>n f>n nf>n U>N P>U
Yawning n > s n > f
Emotional
outburst
Hands/arms
Moving hand/
head towards
stick
S>N f>n NF>N u>n
Rejecting the stick S > N f > n nf > n u > n
Body
Interrupting
motor action
Being physically
active
n>f
Showing
stereotypies
Vocalisations
Positive
Negative n>p
Uninterpretable
All vocalisations p>u
Note: Capital letters indicate a large effect size (EF > .05). Lower case letters indicate a moderate effect size (0.3 > EF > .05).
Abbreviations: F or f, food; N pr n, neutral stimuli; NF or nf, non-food; P or p, pleasant; S or s, scented stimuli; U or u, unpleasant.
8PETITPIERRE ET AL.
Published for the British Institute of Learning Disabilities
3.3 |Response to odorants a priori rated as
pleasant or unpleasant by typical adults
A comparative analysis was carried on four pleasant (Nutella, lily of the val-
ley, rose and strawberry) versus four unpleasant (garlic, sweat, hand san-
itizer and cheese) stimuli. Since pleasant odours that are too strong can
become unpleasant and vice versa, it was essential to ensure that, for this
analysis, the two categories of stimuli had a rather similar average inten-
sity. The latter amounts to 5.71 for stimuli rated as pleasant and 5.59 for
those rated as unpleasant, respectively. A stimuli pleasantness effect was
confirmed in 3 of the 21 indicators. Participants made significantly more
pouts when they were exposed to stimuli rated as unpleasant (Z=3.54,
p=.000),theeffectsizebeinglarge(r=.53). In contrast, they spent more
time exploring the stimuli with their mouth (Z=2.26, p=.024), and
vocalising (Z=2.16, p=.038), in the pleasant condition, the effect sizes
being moderate (r=.34 and r=.33, respectively).
Significant effects of the four aforementioned pleasant stimuli versus
neutrals were observed in 4 of the 21 indicators (see online Supplement 3
fordetails).Theeffectsizewaslarge(r> .50) for one indicator (head align-
ment on the stick) and moderate (rbetween .30 and .49) for three others
(smiling; sniffing; negative vocalisations). Head alignment, smiling and
sniffing prevailed in the pleasant condition compared to the neutral one;
conversely negative vocalisations prevailed in the neutral condition. The
effect of unpleasant versus neutrals was observed in 5 indicators out of 21
see online Supplement 4 for details). One indicator (pouting) shows a large
effect size (r> .50). Effect sizes were moderate (rbetween .30 and .49) for
the four other indicators (head alignment on the stick; moving the lips or
tongue; moving the hand or head towards the stick; rejecting the stick).
3.4 |Influence of moderators on the olfactive
response
The influence of moderators like gender, age, aetiology, presence of
epilepsy, feeding mode, vulnerability to nausea, as well as the link with
MIPQ scores, was explored. The analyses were performed on the nine
behaviours significantly highlighted in the first analysis. No effect of
age, aetiology, presence of epilepsy, feeding mode, vulnerability to
nausea, was found. In contrast, a simple gender effect was found on
the alignment of the head on the stick, since girls stay aligned longer
both in the odorous and in the neutral condition, but both boys and
girls stay longer on the odorous sticks than on the neutrals
(t=2.72, p=.013). Feeding mode moderates the participants' fre-
quency of hand or head movements towards the stick (t=2.50;
p=.021). Participants eating blended or chunky food make more
movements towards the sticks than participants who are fed with a
tube, either partially or totally. However, all participants, no matter
how they eat, make more movements towards the odorous sticks
compared to the neutrals (Figure 1a). Participants assessed with a high
positive mood score make more movements towards the sticks
(Figure 1c) than participants who exhibit low positive mood
(t=2.14, p=.045). On the contrary, participants assessed with a
high positive mood score (Figure 1d) or level of interest (Figure 1b)
exhibit shorter head alignment on the stick behaviours than those
reported with lower positive mood (t=2.82, p=.010) and interest
level (t=5.02, p=.000). However, all align the head longer on the
odorous stimuli compared to the neutrals.
4|DISCUSSION
Despite the importance of olfaction in human functioning, only very
few studies have explored the olfactory behavioural responses of peo-
ple with PIMD. The scope of this research was to systematically
observe how children and young people respond to odours and
whether certain factors were likely to influence their response. The
overall results show that participants respond significantly differently
to odorous compared to odourless stimuli. They also show significant
differences according to the types of stimuli, whether food or non-
food, pleasant or unpleasant. Table 4 summarises their responses
under the various conditions.
In children and young people with PIMD, the reaction to odours
is mainly manifested by the alignment of the head on the odour,
sniffing, pouting, nose/hand coordination on the stick, moving the
hand or head towards the stick and rejecting the stick. When the
scent is presented to them, the participants significantly align their
head on the stick, whether it is food, non-food, pleasant or even
unpleasant odours. Odorous stimuli, except those rated as unpleasant
by typical adults, have an effect on the number of sniffs, which are
more numerous in the odorant condition than in the neutral one. To a
lesser extent, exploring with the mouth, chewing and moving the lips
or tongue, show that the two conditions are approached differently.
Smiling is significantly more manifested in the presence of non-food
stimuli, as well as with stimuli rated as pleasant. On the contrary,
pouting appears more often in the presence of unpleasant stimuli.
Pouting also differentiates between odours rated by typical adults as
pleasant and unpleasant. Yawning appears significantly more often in
neutral conditions, which may suggest boredom in the absence of
interesting events. Being physically active and making uninterpretable
vocalisations, significantly more manifested during neutral conditions,
can likewise be seen as a means to react to the vacuum of stimulation
or to the disappearance of the interesting stimulus. Results show a
parallel between movements to bring the stimulus closer or further
away. Both occur in the presence of various stimuli, including those
rated as unpleasant. These oriented movements suggest that the per-
son identifies the location of the stimulus and, perhaps seeks to act
actively on it. The nose/hand coordination on the stick is an attempt
to explore it by stabilising both the head and the odorous source.
Behaviours are stable and consistent between and within the various
odorous conditions.
The results, showing behavioural differences between pleasant
versus unpleasant, food versus non-food groups of stimuli, imply the
possible existence of an early implicit categorisation ability in the par-
ticipants. Along with discrimination, categorisation is the second basic
process investigated in infant olfactory perception (Schaal
et al., 2002). Discrimination is the ability to respond selectively to
PETITPIERRE ET AL.9
Published for the British Institute of Learning Disabilities
specific individual odours, while categorisation means to ‘group dis-
criminable properties, objects, or events into classes (…)’(Rakison &
Lawson, 2013, p. 4) and to respond to groups of odours. A large num-
ber of studies highlight the possibility that categorical abilities exist
already at the very onset of development and may be expressed ‘in
concept-like behaviours’(Alessandroni & Rodriguez, 2020, p. 2). In
the present research, the setting was not specifically designed to
observe the participants' categorical abilities and it would be
unsuitable to overreach the findings in terms of mechanisms underly-
ing the behaviours observed; even so, given the clear differential reac-
tions between both groups of stimuli, and by analogy with the
developmental data, the presence of prelinguistic categorisation abili-
ties cannot be excluded.
With regard to whether moderating variables affect responses,
we find girls align the head longer on the stimuli. Head alignment
however significantly reflects the ability to detect odorous versus
neutral stimuli in both genders. It was also interesting to observe that
attempts to get closer to the stick are more numerous in the odorous
compared to neutral conditions and that capture attempts differ
according to the participant's feeding mode. Several explanations are
possible regarding this result. The meal is a situation with a great
wealth of odours in which children are often encouraged to grasp (the
food or the utensils). Compared to neutral stimuli, it is possible that
our odorants, which included a lot of food odours, generated reaching
behaviours by analogy to what happens during mealtimes. We can
also assume that, even if they do not handle the spoon themselves,
spoon-fed children have a more sustained experience of contact with
food than enteral-fed children. However, most children, enteral-fed
children included, have an experience with spoon-feeding. This could
explain why the odorous condition elicited more reactions than the
neutral, though to a lesser extent in children who were artificially fed
at the time of the study. We were surprised to find that participants'
head alignment duration was inversely related to the interest and the
positive mood sub-scores, respectively. A positive relationship
between the two dimensions would have been more logical. On the
other hand, our results are based on direct observations, while the
MIPQ is a reported retrospective measure; the nature of the data
therefore differ considerably. In addition, positive mood behavioural
manifestations, as well as interest ones, may be more or less salient
from one person to another. It is possible that some children express
their interest in a very discreet way, by simply positioning themselves
in front of the source of a stimulation, while others express them-
selves through more easily observable behaviours. The difference in
procedure sensitivity may explain this result, which however does not
challenge the fact that the two groups express a clear difference
between the two stimulation conditions, regardless of their level of
interest or positive mood.
This research is not free from limitations. It focuses on odour
detection using only a single concentration, which is a rather simpli-
fied way to observe human olfactory functioning. Prior olfactory
experience should have been controlled better. Finally, group analyses
are reductive and do not provide access to individual clinical realities.
We observed, for instance, a nauseous response in one participant.
This response occurs twice while presenting the same single odorant
(strawberry) 2 weeks apart. An anamnesis revealed that this partici-
pant, fed by gastric tube at the time of the study, had taken
strawberry-odorous food supplements a few years before. Her reac-
tion suggests the integrity of an olfactive memory, which is very inter-
esting from a clinical point of view.
However, the study has the merit of drawing attention to a
neglected sensory modality in people with PIMD. On the research
level, many questions remain open. The function of odours for this
population should be further investigated, for example whether some
odorants are calming, whether they provide a feeling of security or,
on the contrary, evoke an unpleasant experience as in the anecdotal
observation reported. The influence of medication should also be
studied because some drugs act on olfaction. Studying children's and
young people's reactions to familiar versus unfamiliar people's odours,
or to their own odour versus that of peers, could be interesting in
order to provide access to their self- and other awareness capacities.
On the educational level, the results support recommendations to use
odorants with this population and provide guidelines to observe and
interpret their responses.
ACKNOWLEDGEMENTS
We express our gratitude to all participants, their families and their
schools, in particular the Clair Bois Foundation which initiated the
study and the Givaudan Foundation which made it possible thanks to
its financial support.
DATA AVAILABILITY STATEMENT
Data available on request due to privacy/ethical restrictions.
ORCID
Geneviève Petitpierre https://orcid.org/0000-0002-3353-897X
Juliane Dind https://orcid.org/0000-0002-8378-5944
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SUPPORTING INFORMATION
Additional supporting information may be found in the online version
of the article at the publisher's website.
How to cite this article: Petitpierre, G., Dind, J., De Blasio, C.,
& Gremaud, G. (2021). Odour detection in children and young
people with profound intellectual and multiple disabilities.
Journal of Applied Research in Intellectual Disabilities,1–12.
https://doi.org/10.1111/jar.12963
12 PETITPIERRE ET AL.
Published for the British Institute of Learning Disabilities
