Real and Imagined Smellscapes

Abstract

The smellscape is the olfactory environment as perceived and understood, consisting of odours and scents from multiple smell sources. To what extent can audiovisual information evoke the smells of a real, complex, and multimodal environment? To investigate smellscape imagination, we compared results from two studies. In the first, onsite participants ( N = 15) made a sensory walk through seven locations of an open-air market. In the second, online participants ( N = 53) made a virtual walk through the same locations reproduced with audio and video recordings. Responses in the form of free-form verbal annotations, ratings with semantic scales, and a ‘smell wheel’, were analysed for environmental quality, smell source type and strength, and hedonic tone. The degree of association between real and imagined smellscapes was measured through canonical correlation analysis. Hedonic tone, as expressed through frequency counts of keywords in free-form annotations was significantly associated, suggesting that smell sources might generally be correctly inferred from audiovisual information, when such imagination is required. On the other hand, onsite ratings of olfactory quality were not significantly associated with online ratings of audiovisual reproductions, when participants were not specifically asked to imagine smells. We discuss findings in the light of cross-modal association, categorisation, and memory recall of smells.

Full text

fpsyg-12-718172 December 24, 2021 Time: 13:18 # 1
ORIGINAL RESEARCH
published: 24 December 2021
doi: 10.3389/fpsyg.2021.718172
Edited by:
Antonella Radicchi,
Technical University of Berlin,
Germany
Reviewed by:
Jieling Xiao,
Birmingham City University,
United Kingdom
Dmitrijs Dmitrenko,
University of Sussex, United Kingdom
*Correspondence:
PerMagnus Lindborg
pm.lindborg@cityu.edu.hk
Kongmeng Liew
liew.kongmeng@is.naist.jp
Specialty section:
This article was submitted to
Environmental Psychology,
a section of the journal
Frontiers in Psychology
Received: 31 May 2021
Accepted: 08 November 2021
Published: 24 December 2021
Citation:
Lindborg P and Liew K (2021)
Real and Imagined Smellscapes.
Front. Psychol. 12:718172.
doi: 10.3389/fpsyg.2021.718172
Real and Imagined Smellscapes
PerMagnus Lindborg1*and Kongmeng Liew2*
1SoundLab, School of Creative Media, City University of Hong Kong, Kowloon, Hong Kong SAR, China, 2Social Computing
Laboratory, Division of Information Sciences, Nara Institute of Science and Technology, Ikoma, Japan
The smellscape is the olfactory environment as perceived and understood, consisting
of odours and scents from multiple smell sources. To what extent can audiovisual
information evoke the smells of a real, complex, and multimodal environment? To
investigate smellscape imagination, we compared results from two studies. In the first,
onsite participants (N= 15) made a sensory walk through seven locations of an open-
air market. In the second, online participants (N= 53) made a virtual walk through
the same locations reproduced with audio and video recordings. Responses in the
form of free-form verbal annotations, ratings with semantic scales, and a ‘smell wheel’,
were analysed for environmental quality, smell source type and strength, and hedonic
tone. The degree of association between real and imagined smellscapes was measured
through canonical correlation analysis. Hedonic tone, as expressed through frequency
counts of keywords in free-form annotations was significantly associated, suggesting
that smell sources might generally be correctly inferred from audiovisual information,
when such imagination is required. On the other hand, onsite ratings of olfactory quality
were not significantly associated with online ratings of audiovisual reproductions, when
participants were not specifically asked to imagine smells. We discuss findings in the
light of cross-modal association, categorisation, and memory recall of smells.
Keywords: smellscape, environment, perception, smell, imagination, memory, crossmodal
INTRODUCTION
The term ‘smellscape’ was introduced by Porteous (1985), based on Schafer’s (1977) soundscape
concept. It refers to the olfactory environment as perceived and understood by a person influenced
by memories and past experiences, specific to its context (Xiao et al., 2018, p. 106). When
considering living spaces and everyday environments, the quality of the olfactory environment is
important both psychologically, e.g., subjective evaluation, and physiologically, e.g., stress recovery
(Annerstedt et al., 2013;Hedblom et al., 2019). Thus, an examination of the smellscape may
contribute towards our understanding of the relationship between perceptual processes such as
odour annoyance as well as general wellbeing (Naddeo et al., 2013). Smells are closely associated
with memories (Wilson and Stevenson, 2003;Herz, 2016). As the senses combine to influence our
overall experience in everyday environments (Spence, 2020, p. 2) throughout our lives, memories
contain cross-modal information that was concurrently encoded. Specifically, auditory, visual,
and olfactory memories are interrelated. As olfactory perception exerts a large influence on the
subjective evaluation of environments, we posit that when presented with either visual and/or
auditory information, smells can be imagined to match this visual/auditory information, which
would in turn exert an influence on the subjective evaluation of a particular environment.
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SMELL PERCEPTION
Humans have several neurological systems to collect information
about the environment (Spence, 2020, pp. 8–9). The olfactory
system detects airborne semiochemicals (i.e., odours and scents)
in particular in the orthonasal region at the front of the nose;
the trigeminal system detects strong irritators (e.g., ammonia or
chilli); and the vomeronasal (accessory) system detects chemicals
in fluids, including pheromones (Haviland-Jones and Wilson,
2010;Lundström et al., 2011). The number of genes expressing
odour detection through the nose constitutes one of the largest
gene families in the genome (Buck and Axel, 1991, p. 183),
perhaps up to 3% of the total genome which would make it second
only to the immune system (Haviland-Jones and Wilson, 2010,
p. 236). The human sense of smell compares rather favourably
with that of dogs and rats (see McGann, 2017, for a review),
and its discriminatory powers might be several magnitudes larger
than what was previously believed (Bushdid et al., 2014).
The terminology pertaining to olfactory stimuli is inconsistent
in the literature. Terms such as ‘odour’ and ‘smell’ sometimes
appear to be used interchangeably (e.g., Haviland-Jones and
Wilson, 2010;Bruce et al., 2015) and regardless of their valence;
however, ‘malodour’ is specifically negative, while no such
negation can be attached to the word ‘smell’. Likewise, Belgiorno
et al. (2013) define ‘odour’ as an “organoleptic attribute [property
of liquids, air, and other substances, that is] perceptible by the
olfactory organ” (p. 15), and elsewhere appear to use ‘smell’ with
the same meaning. Spence (2020) omits ‘odour’ in favour of
‘scent’, and in his review of design approaches to the olfactory
environment appears to use ‘smell’ more often negatively, and
‘scent’ (or ‘fragrance’) in positively valenced contexts. Discussing
olfactory imagery, Young (2020) consistently uses ‘smell’ when
referring to the percept, and words such as ‘olfaction’ in the
context of active sensing of the environment; the latter distinction
is also made by Xiao et al. (2018).
Smells communicate. Smells have a strong effect on
individuals, and may even induce emotional responses for
unattended stimuli in a pre-conscious manner (Haviland-Jones
and Wilson, 2010, pp. 237–238). Compared to visual and
auditory stimuli, there has been much less of a consensus in
quantifying olfactory stimuli for empirical analyses. Naddeo
et al. (2013) proposed six parameters for characterising smells:
by concentration, perceptibility threshold, intensity, diffusibility
or volatility, quality, and hedonic tone. Of interest to the present
study are intensity (perceived as strength), quality (or character),
and hedonic tone (overall pleasantness or unpleasantness of a
smell, and its resultant perceptual ‘acceptability’; cf. Dravnieks
et al., 1984;Xiao et al., 2018).
The specific quality or character of a smell is often expressed
via semantic descriptors, for example ‘fruity’ or ‘medical’
(Naddeo et al., 2013, p. 14). As with all sensory channels,
olfactory sensation is mediated through individual factors,
previous experience, and attention. Language embeds salient
experiences and mediates between sensation and cognition,
though a distinction needs to be made between different forms
of cross-modal correspondences: what Deroy and Spence (2016)
labelled statistical, structural, semantic, and hedonic (emotional)
mediation mechanisms. If we accept the principle of the Lexical
Hypothesis – that socially relevant characteristics of personality
are encoded in natural language because this benefits social
structures and individual survival (see John and Srivastava, 1999,
for a review) – then salient odours in the environments need also
to be communicated and understood within a linguistic group
or culture for much the same reasons. This approach allowed
the development of odour classification schemes, for example
McGinley’s Odor Descriptors Wheel (McGinley and McGinley,
2002), which was employed in the present study.
People typically describe and categorise smells by perceived
source (e.g., fishy, floral) but they also use words that describe
the effect a smell has on them (e.g., nauseating, pleasant). Several
categorisation studies have observed that people’s default mode
of perception is ecological; that is, we tend to interpret sensation
in terms of causes, as evidence of events and actions in the
environment. For auditory perception, ecological conditioning
over the lifetime lies behind the default mode of causal (or
connotative) listening (Schaeffer, 1966;Chion and Gorbman,
2009;Tuuri and Eerola, 2012; see Lindborg, 2019, for a
discussion). In this regard, olfaction appears to work much in the
same way as auditory perception (e.g., Bruce et al., 2015;Deroy
and Spence, 2016;Xiao et al., 2020) in that both the attributed
external source and its subjective affect can be verbalised
(Lindborg, 2016). As with causal identification of sound
sources, an evaluation of smell sources follows immediately and
automatically upon source identification (Waskul and Vannini,
2008;Xiao et al., 2020, p. 11) and probably regardless of whether
the identification was correct or not (Herz, 2016). Dravnieks et al.
(1984) determined the hedonic score (i.e., pleasantness) of 141
commonly encountered smells from ratings by 429 participants.
Note, however, that people often cannot identify or use accurate
descriptions to define smells or smell-sources, especially in a de-
contextualised condition (Xiao et al., 2020), and that unconscious
detection of smells most probably also contributes to the overall
perception, though it might depend more on the trigeminal than
the olfactory system proper (Jacquot et al., 2004, p. 51).
Congruence between sensory information channels leads to
perceptual processing fluency which in turn is associated with
positive evaluation (Reber et al., 2004;Spence, 2020, p. 2). It has
been suggested that concurrent visual information can increase
the ability of smells to arouse emotions, and that visuals without
smells might evoke odour-related memories (Ehrlichman and
Bastone, 1992). Gottfried and Dolan (2003) revealed neurological
evidence for perceptual olfactory facilitation when semantically
congruent visual and odour stimuli were presented. Castiello
et al. (2006) investigated the cross-modal influence of smells
on vision and motor activity. They presented people with a
smell and then tasked them to grasp with their hand a virtual
visual object. The imagined size of the smelly object influenced
the size and shape of the hand as it was moved towards the
visual object, showing that odours can cross-modally affect
kinematics. Xiao et al. (2020, p. 14) wrote that “smellscapes are
representations of individuals’ imaginations of places, triggered
by smells in a space-time structure”. There is evidence that smells
can trigger episodic memory recall (Herz, 2016) and that smells
congruent with audiovisual displays can generate more positive
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response behaviour within a context of virtual tourism (Flavián
et al., 2021). Might this cross-modal influence from smell to
other senses be activated in reverse? Considering a theoretical
framework for multi-modal mental imagery, Young (2020)
posited that non-olfactory stimuli can trigger smell memories,
which are projected as imagined smells.
Considering the above, we investigated if people can make
meaningful smell associations when presented with purely
audiovisual material. The present article discusses results from
two recent studies of the smellscape at a complex multimodal
environment, real and imagined. The first is a ‘sensory walk’
conducted onsite, with participants walking through seven
locations while making observations. The observations from
the first study functions as a reference or ground truth for
the second study, which is a ‘virtual sensory walk’ conducted
online, where the same locations were reproduced with audio
and video recordings. Analysis of response data from the real
environment provides a baseline against which ratings of the
virtual environment were gauged (cf. Annerstedt et al., 2013).
The online environments were represented in three conditions:
audio-only, video-only, and audiovisual (i.e., movie). We were
interested in determining the quality, strength, and hedonic tone
of the smellscapes evoked and imagined (Naddeo et al., 2013).
MATERIALS AND METHODS
Sensory Walk
Sensory walk and sensewalk are terms describing an activity
whereby people move through a physical environment making
observations with a research purpose. A soundwalk focuses
on the acoustic environment and a smellwalk focuses on the
olfactory environment. All are methods for onsite data collection
that allow researchers to systematically investigate how people
experience, understand, and utilise spaces (Henshaw et al.,
2009, 2010;Bruce et al., 2015;Koseoglu, 2016;McLean, 2017;
Xiao et al., 2020). The methodology originates in soundscape
studies (Schafer, 1977) and has been broadened out to consider
multimodal aspects of environments (Bruce et al., 2015, p. 100;
Quercia et al., 2015). Carefully curated smellwalks can take the
form of experience design (see Aggleton and Waskett, 1990) or
as “walkalong interviews in different contextual spaces” (Xiao
et al., 2020, pp. 15–16) that aim to generate an ecologically
valid vocabulary for further semantic and cross-modal analysis.
Porteous (1985, p. 360) suggested that while a soundscape
consists of sound sources evidencing events, a smellscape should
be understood as the sum total of numerous smell sources that
each may connote cause and effect. While a soundmark is a sound
that is intimately linked to a site and carries meaning for its
community, a smellmark would correspondingly be a culturally
highly important smell.
Tiong Bahru Market
In order to study the perception of smells within a multimodal
context, we conducted a sensory walk called “Incomplete City
Walks: Coffee Shops and Hawker Centres” (Magiera, 2020)
at Tiong Bahru Market in Singapore. Perhaps more than
in other countries, open markets (aka ‘wet markets’) are
socially important to Singaporeans because they are spaces
for unmediated, non-political interactions (Mele et al., 2015).
The history and significance of Tiong Bahru Market in this
context was the main reason for choosing the site. Houses and
shophouses appeared at the site of current-day Tiong Bahru
Market around 1900. A nearby cemetery provided its name:
‘tiong’ (
亯
) means “to die’ in Hokkien (the most prevalent
language and culture until the 1980s) and the Malay word
‘bahru’ means ‘new’. By the 1930s roads, drains and culverts
had been constructed, and one of the first public housing estates
in Singapore was opened at Tiong Bahru in 1936. During this
time, the area was also known as Mei Ren Wo, “den of beauties’,
with musician-entertainers doubling as prostitutes referred to
as ‘pipa girls’. It was generally considered an unseemly and
unhygienic place. The marketplace roof was made up of palm
leaves woven together, and the surrounding huts had thatched
roofs (National Heritage Board, 2013). Tiong Bahru Market
reopened in 2006 after thorough renovations over more than a
decade (CPG Consultants, 2005). At present it sports a triangular-
shaped architecture in three levels: the ground level has a wet
market, shops selling vegetables, flowers, clothing, and hardware,
and a green space; the second level has a large food court, a.k.a. a
hawker centre; and the rooftop has a Carpark (Bravo, 2021).
Locations
Seven locations at Tiong Bahru Market were identified as having a
strong identity in terms of smells and sounds. In the present text,
they are labelled (in alphabetical order) Carpark, Flowers and
Meat, Food Court, Garbage, Green Core, Stores, and Wetmarket.
See photos in Figure 1 and map in Figure 2.
Onsite Sensory Walk
Participants and Procedure
We posted a call on social media to participate in an early
morning sensory walk at Tiong Bahru Market, saying “In this
structured sensory walk we explore a public space differently,
outside of routines and habits. Moving slowly between locations
affects our sense of architecture, spatiality, and time. Standing still
and focussing on sound and scent increases our awareness of the
physical environment. What do you hear? What do you smell?
What do you experience?”
Fifteen people volunteered. Their mean age was 36 years
(SD = 12), in a range between 22 and 53; there were nine
females and five males (and 1 ‘other, or prefer not to say’). As
for present occupation, nine self-reported as artists, educators,
or researchers, and two were students. They had mixed levels of
previous experience with sensory walks or soundwalks: four had
‘never tried’, five had participated at a similar experience within
the past month, and three had done so at an earlier point in time.
The participants gathered at 6.30 am, 3 December 2016,
and were informed about the task and signed a consent form.
None of the participants was smoking tobacco before or during
the sensory walk. The group was divided into three groups of
five, each led by the two authors and an assistant. The three
groups of five completed the sensory walks among the seven
selected locations of the market in a different, pseudo-random
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FIGURE 1 | Photos of the seven chosen locations at Tiong Bahru Market.
order. The whole walk took between 70 and 90 min that is,
10–14 min at each location. Moving from one location to the
next took a few minutes (especially when walking stairs between
levels. Upon reaching a new location, the group leader made
sure the five participants stayed relatively close together and
within the target area for around 7–8 min. Each participant
carried a small support plate (A5 size) with the seven locations
on separate pages arranged in the order of visit pre-planned
for each of the three subgroups. They marked responses with
a pencil while standing; the market did not have any benches
to sit down on, except at the Food Court. At each location,
the participants spent the first 2–3 min focussing on being still
and taking in the environment, then 3–4 min on writing down
their impressions, and finally, they were at ease for a few more
minutes before the group leader signalled for the group to move
on. The participants were admirably concentrated throughout the
sensory walk, and a little after 8 am gathered for a debriefing over
traditional breakfast.
Annotation Protocol
At each location, the protocol first required an evaluation of
the quality of the sonic, visual, and olfactory aspects of the
environment. Participants marked a response on a seven-step
Likert scale anchored by “Very good” and “Very bad”, with
“Neutral” in the middle. Secondly, they were required to describe
“the most faint or secretive smell (or sound); the most loud
or dominant smell (or sound); the most beautiful or precious
smell (or sound); and the most ugly or disgusting smell (or
sound)”. That is, they were free to annotate sources and events
in either of the two modalities, in relation to the four given
pairs of adjectives that had been set up as opposites. Third and
last, participants were asked to describe, in a few words, their
thoughts and feelings while being in the present environment.
The above three responses or annotations are the ones of
relevance to the present context; other parts of the protocol
that related to soundscape will not be further discussed here.
A sample page is included in Supplementary Data Sheet 1.
It should be noted that asking participants to focus on smells
(either real or imagined) might mask the full range of odour
effects, because verbal explicitation focuses on learned semantic
processes (see Haviland-Jones and Wilson, 2010, p. 239 for a
discussion). Methods for onsite data collection were approved
by the Institutional Review Board of Nanyang Technological
University #IRB-2015-10-056.
The raw collected data from the two studies, anonymised, are
available in Supplementary Data Sheet 2, 3. For convenience, a
code script is given in Supplementary Data Sheet 4 to facilitate
retrieval and pre-processing of the data.
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FIGURE 2 | Overview of Tiong Bahru Market marking out the seven locations of the sensory walk.
Online Virtual Smellwalk
Participants
Participants were recruited from Prolific.co and pre-
screened for nationality (discussed below), age (minimum
18), and educational level (minimum completed Bachelor
degree). Fifty-three valid responses with no duplicates
were collected in March and April 2021. Each participant
gave their informed consent and received a payment. All
reported having no impairment of hearing or vision (wearing
glasses/lenses was okay), being in a distraction-free environment
during the survey, and using quality headphones (earbuds
were discouraged).
Since the environment at Tiong Bahru Market is strongly
characteristic of South-East Asia, we chose to recruit participants
who may be culturally familiar (see Mele et al., 2014). We
first recruited a batch of 25 Singaporean nationals, but upon
a stagnation in signup rates, expanded our recruitment criteria
to include a second batch of 26 participants from neighbouring
Malaysia and Indonesia (that arguably share similar cultural
attitudes towards wetmarkets; see Lim, 2004). It should be noted
that Prolific.co is a United Kingdom-based company and that
it mainly sources its pool of volunteers in Western countries.
A minority of the participants were residing in their home
country at the time of the survey; all were in countries that are
indexed among the first 27 in UN’s list of Developed Countries,
including Singapore, Malaysia, and Indonesia. For example, 25
participants were based in Great Britain, 8 in Germany, and 6
in Australia. Finally, two Hong Kong residents (not the authors)
who had volunteered as beta-testers were included, bringing the
total number of participants to 53.
Their median age was 27 years, in a range between 19 and 54;
there were 36 females and 17 males. As for present occupation,
19 were employed (e.g., medicine, education, business) and 28
students (similar domains), while the remaining 6 self-reported
as homemakers or unemployed. English was the home language
for 33 participants, followed by Bahasa for 12 (spoken in
Malaysia and Indonesia), while the remaining 8 reported
Chinese (the given options included Mandarin, Cantonese, and
Hokkien). Probably reflecting behaviours in their current place
of residence rather than those of South-East Asia, participants
reported infrequently visiting an open-air market (for shopping,
eating/drinking, or buying things), with the most common
response being “Once a month” followed by “Once a year”. As for
ethnicity, 18 out of the 25 Singaporeans self-reported as Chinese,
while on the other hand only 5 of the 28 other participants
considered themselves Chinese (note that the second batch
consisted of Malaysian and Indonesian nationals). The median
time to complete the survey was 30 min, in a range between 14
and 62. They were paid according to the recommended Prolific
hourly rate, which came out to be 6.25 GBP per person.
Materials
Video and sound materials for all stimuli used in the online
study were captured at the same time that the onsite study was
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conducted, that is, in the early morning of 3 December 2016.
The first author carried handheld recording equipment which did
not detract from the role of (silently) leading the small group of
five participants from location to location. Similarly, the Sound
Pressure Level (SPL) meter was carried by the second author.
In post-production, we edited a representative sequence of each
location as a short movie of 90 s duration. Care was taken to
create a naturalistic visual representation with an objective point
of view, and to keep the sound levels proportional to what had
been measured onsite with the SPL meter. We then created ‘audio
only’ and ‘video only’ sets by replacing the original video with
a medium-gray Gaussian blur and the original audio with low-
level pink noise. This yielded 21 stimuli, i.e., seven scenes in
three modes (referred to as audio, video, and movie). Note the
importance of adding low-level yet audible noise to the ‘video
only’ stimuli, since previous research has shown that a realistic
visual feature without any sound at all can bias participant
perceptions towards fear, and make them expect something
dangerous to appear (Annerstedt et al., 2013).
Procedure
A survey was designed using QuestionPro1. The 21 stimuli were
presented in two parts. First, an individually randomised part
containing the seven Audio and the seven Video clips; then, an
individually randomised part with the seven Movie clips. In this
way the order effect of bimodal stimuli giving unwanted clues
to their unimodal versions was avoided. For each stimulus, the
participant was requested to go full-screen, start the movie (which
could be greyish video with naturalistic audio, or video with low-
level noise, or naturalistic audio and video together), and imagine
that they themselves were actually in the present environment.
The survey constituted an ‘onsite virtual sensory walk’, which we
can compare with the onsite walk (functioning as ground truth).
Participants were given three tasks to evaluate the audiovisual
environment presented to them.
•The question “Overall, how pleasant is this environment?”
was intentionally a broad, multimodal quality evaluation
that did not specifically require them to imagine
smells. They responded using a seven-step Likert scale
anchored by “Very unpleasant” and “Very pleasant”, with
“Neutral” in the middle.
•The instruction: “In your own words, describe the
smells that you imagine”, with responses in the form of
annotations of free associations, was intended to direct
their attention specifically to the smells they might have
imagined from audio-visual information.
•The Odor Descriptors Wheel (McGinley and McGinley,
2002) was displayed, in a slightly adapted layout (see
Figure 3), and the participant was required to “Please
click on the smell types that you imagine in this
environment”. They could mark up to three smells by
mouse-clicking (the average number of clicks per stimulus
and participant was 2.6).
1www.questionpro.com
Note that the first two tasks provided two angles onto the
phenomenon of how audiovisuals elicit smell imaginations,
which we have suggested can explain the results in the statistical
analysis further below. Note that no olfactory stimuli were
presented to the participants, who only imagined the smells.
After completing all 21 stimuli participants self-reported
demographic information (the group profile is reviewed in the
“Participants” section above). Online data collection procedures
were approved by the Ethics Committee of City University of
Hong Kong, #13-2020-08-E.
RESULTS FROM ONSITE AND ONLINE
STUDIES
Onsite: Real Smells
The results from the onsite study functions as a ‘ground
truth’ against which the results from the online study can be
interpreted. Therefore it is firstly of importance to explain how
the onsite participants (N= 15) described their experience at
the seven locations. The general experience of the environment
was annotated by the onsite participants in free-form verbal
descriptions. The locations had clearly different characteristics
and we will discuss their olfactory aspects by citing representative
annotations verbatim.
•Carpark: this location was described in mostly visual terms,
e.g., “View – sense of open space, aerial, above”.
•Flowers and Meat: this is a mixed-market area that evoked
spatial and olfactory annotations, e.g., “meat – stronger
smell”, “The smell is totally different in flower to meat
area”, and “Flowers do not smell as strong as I usually
experience @Flower hawkers” highlighting an activity-
related expectation.
•Food court: this is a typical Singaporean-style ‘hawker
stalls’ area serving various kinds of local food. It engaged
all sensory modalities, though as one participant wrote:
“here, smells of foods cooking dominate other senses. Must
be ready for breakfast!”, while another highlighted the
continuous, open-air character of Tiong Bahru Market:
“Olfactory, continuous with car park [on Level 3], but
not L1 market”.
•Garbage: as discussed in the section about environmental
quality ratings, it was generally considered unpleasant.
However, the smells were not necessarily as strong or
bad as some appear to have expected: “It was quite
monotonous in the sense that I didn’t feel much for
that place [Garbage] despite attempting to discover its
sounds and smells”. Meanwhile, another person tried to
“focus specifically to LISTEN [and this] makes it a more
pleasant experience, and I didn’t notice the smell at all as I
normally (probably) would”. Lastly, one person remarked
that it was “interesting how smells move from place to
place, as does sound”, highlighting the characteristic spatial
pervasiveness and temporal continuity of smell – these
characteristics are stronger for smell than for sound, and
clearly more so than for light.
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FIGURE 3 | The ‘smellwheel’ used in the present study (adapted from McGinley and McGinley, 2002).
•Green Core: the small park is at the connecting centre
between other locations. Smells and sounds reach it from
all directions and cause blurred sensations. One participant
characterised it as “. . .a hot pot of noise. Everything can be
heard but cannot be heard clearly at any one time. Nothing
makes sense”, and the same may have been the case for
smells, e.g., “Smell – dense; Busy; Sound – interesting”.
For at least one participant, their expectation of a ‘park
smell’ was not met: “Wish i could smell the wet grass over
the raw meat”, perhaps indicating that the smell of raw
meat was still dominating even though the row of butchers
was some 20 m away.
•Stores: this location is a row of small shops along a street.
Here, participants mostly noted sonic elements, such as
the background music played in the small shops. One
participant reacted strongly to the “SMELL of incense shop
at [the] end of [the] row [which] gave me an immediate
headache and this created a strong negative association
with what had been super-pleasant. The changing music of
the stalls, as I walked along, was calming and gave joy”.
•Wetmarket: this is an area selling fish and seafood.
Annotations revealed marked expectations about the
odours, but also that “fish variety of colour doesn’t
correspond to smell”, perhaps indicating that smells
tended to blend together. One person annotated a specific
‘precious’ source (see below) as “Delicate smell of dried
scallops, cuttlefish”, but to most of the participants in
this study the Wetmarket smells were simply generically
‘fishy’ and did not distinguish themselves. An intriguing
observation about social communication habits was that
“People seem to talk more with their fishmongers than
[with their] butchers”. Previous research has noted that
the observed activities lead people to expect and imagine
particular sounds and smells in certain areas (e.g., Bruce
et al., 2015, p. 8).
Environmental Quality
The onsite participants (N= 15) rated the perceived olfactory
quality of the environment, as well as the visual and sonic
aspects of the environment. Multivariate analysis of variance
(MANOVA) revealed that quality ratings (i.e., olfactory, visual,
and sonic) differed between the seven selected areas of the
open market [Pillai’s trace (6 df) = 0.677, F(18,222) = 3.60,
p= 0.000003]. This significant result allowed us to follow up
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with a two-way within-participants ANOVA, taking Quality
as the dependent variable and Location and Modality as the
independent variables. Each of the independent variables was
strongly related to the dependent variable [Location: F(6) = 8.56,
p= 0.00000002; Modality: F(2) = 10.1, p= 0.00006]. Post hoc
analysis with Tukey’s Honest Significant Difference test showed
that Olfactory ratings at the Garbage location were much lower
than those at the six other locations, corresponding to as much
as two or three steps on the seven-step Likert scale. With the
Garbage location removed from the data (keeping the remaining
six locations), Olfactory quality ratings were still significantly
lower than Sonic and Visual quality ratings, as indicated by
Mann–Whitney’s rank-based test on paired ratings (p= 0.031
for Olfactory vs. Sonic; p= 0.0006 for Olfactory vs. Visual). The
differences, respectively, corresponded to 0.53 and 0.86 steps on
the rating scales, with medium effect sizes (Cohen’s d= 0.33 and
0.55 SD). The difference in quality between Sonic and Visual
aspects of the environment was not significant (p= 0.88) across
seven locations, though when Garbage was removed, Visual
quality was marginally higher than Sonic across the six other
locations (0.03 scale steps, p= 0.041) with a small effect size
(d= 0.21) (see Table 1, Col. 1–3, and Figure 4).
It is not immediately obvious why the olfactory environment
received lower quality ratings than both the visual and the sonic
aspects. Note that the participants at the onsite sensory walk
had been tasked to ‘seek out’ the smells, and this might have
predisposed them to be more critical to smells. However, it is
also conceivable that the bias did not originate in the participants’
minds but that it reflects something true about the environment
at Tiong Bahru Market. For example, the market might simply
not be successful in taking care of and promoting the grand
variety of its smellscape in a positive way; rather, it is left
hanging, as it were. The major renovation (CPG Consultants,
2005), and habits of the vendors, might have paid less than
adequate attention to the design of the olfactory environment,
which therefore lags behind the quality of visual or sonic
aspects of the market. For example, a current website promoting
the market (Bravo, 2021) does not highlight its smellscape.
Previous research noted that the odours of fish are generally
expected and accepted as part of the experience of a wetmarket,
regardless of what someone might otherwise think of the smell
of raw fish (Bruce et al., 2015, p. 7). In fact, for Tiong Bahru
Market, the smell of raw fish is a smellmark (Porteous, 1985).
A suitable presentation in marketing material might prepare
visitors (e.g., tourists) and thereby enhance the experiences of
Tiong Bahru market as a whole, benefitting the larger economy
(Henshaw et al., 2016). Attention to the smellscape as part of the
intangible heritage has a potential to benefit ‘virtual tourism’, as
shown by Flavián et al. (2021).
Smell Sources
The onsite participants annotated smell sources at each of the
seven locations and indicated whether they considered them
to be precious (or beautiful), secretive (or faint), disgusting (or
ugly), or dominant (or loud). We chose the four adjectives
because they can be paired two by two, to define bipolar,
orthogonal dimensions labelled precious – disgusting and
secretive – dominant. Thus, in this analysis, precious smells
oppose disgusting smells, and secretive smells oppose dominant
smells. The approach allowed arranging smell sources in a
circumplex, one for each location, as shown in Figure 5.
Note that the circumplex spanned by the four adjectives is
a simple yet adequate approximation to the more complex
smellwheel (Figure 3), where the left-right and low-high
directions are intrinsically congruent with the dimensions in
a standard Valence-Arousal circumplex. That is, high valence
corresponds to more precious; low valence to more disgusting;
high arousal to more dominant; and low arousal to more
secretive. However, be aware that the smellwheel does not
directly yield information about the valence of individual
smells, and can only indirectly be used to indicate the arousal
potential (e.g., intensity) of sources by considering the distance
between the ‘neutral’ centre to a distinct smell type (more
about this below). In Figure 5 the seven locations have
been placed according to the main types in the smellwheel
(compare also with photos in Figure 1). This graphical
TABLE 1 | Mean ratings of environmental quality and hedonic tone in the two studies.
Onsite, environmental quality Online, environmental quality Onsite, hedonic Online, hedonic tone
Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 7 Col. 8 Col. 9 Col. 10
Sonic Visual Olfactory Audio Video Movie Olfactory Audio Video Movie
Carpark 0.88 1.54 −0.31 0.00 0.26 0.09 −0.52 −0.73 −0.08 −0.69
Flowers and Meat 1.14 2.00 1.42 0.00 0.08 −0.45 0.80 −0.43 −0.03 1.81
Food Court 1.12 1.21 1.05 0.28 0.30 0.83 −0.03 0.35 0.16 1.08
Garbage 1.21 −0.83 −1.54 −1.08 −2.23 −1.75 −2.48 −2.43 −4.87 −5.10
Green Core 1.21 1.23 1.27 −0.09 0.42 0.26 0.30 −0.01 0.72 0.36
Stores 1.27 1.19 0.12 −0.11 0.49 0.34 0.00 −0.81 −0.81 −0.50
Wetmarket 1.71 2.11 0.71 0.04 −0.43 −1.30 −1.44 −0.29 −0.41 −3.03
In Col. 1–3 (onsite) and Col. 4–6 (online), values are means of ratings on seven-point Likert scales (numerically limited between −3 and 3), averaged across 15 participants
in the onsite data, and 53 participants in the online data. Values in Col. 7 (onsite, hedonic value, olfactory) were obtained by matching all the onsite annotations of smells
in free-form verbal descriptions with smell descriptors and corresponding hedonic scores in from previously published research (Dravnieks et al., 1984). Scores were
summed for each location and averaged across the 15 participants. Values in Col. 8–10 were obtained by the same method, from free-form annotations in the online
data. They were summed for each location and modality (audio, video, movie), and averaged across the 53 participants in the online study.
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FIGURE 4 | Boxplots of onsite ratings (N= 15) of three aspects of environmental quality for seven locations. Quality was rated on a seven-step Likert scale; see the
text for details.
FIGURE 5 | Onsite smell source annotations (N= 15) for seven locations; see the text for details.
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arrangement supports our interpretation of the locations’ general
environmental characteristics, and facilitates a comparison with
the online responses.
Hedonic Tone
The smell source annotations (in terms of precious – disgusting
and secretive – dominant) allow us to infer which locations
were more liked or more exciting. To estimate the hedonic tone
(pleasantness) for each location, we matched the annotated smells
against the list by Dravnieks et al. (1984), which contains 141
commonly encountered smells with hedonic tone rated on a
nine-step Likert scale by 429 participants. The listed scores range
from −3.75 for “Cadaverous (dead animal)” to 3.53 for “Bakery
(fresh bread)”. Nearly all of our participants’ descriptions could
be matched with items in the list. Notable unmatched annotations
related to the smells of humidity after rain, fresh air, and wind,
all of which likely to have been positively valenced for the onsite
participants. It might be debatable to what extent ‘fresh air’ has
a smell of its own, but one should take note of the fact that
such usage of semantic labels by laymen is systematic (see also
the corresponding analysis of the online data). In the present
calculation of hedonic score, these annotations had to be omitted.
Summing up within each location yielded the values listed in
Table 1, Col. 7.
Online: Imagined Smells
Environmental Quality
In the online study, participants (N= 53) rated the imagined
environmental quality in terms of pleasantness for each of the
21 stimuli, that is, seven locations and three modalities (audio,
video, and movie; see Procedures section). We conducted a two-
way within-participants ANOVA with Quality as the dependent
variable, and Location and Modality as independent variables.
It revealed a strongly significant relation between Quality and
Location [F(6) = 61.3, p<2e-16], but not with Modality
[F(2) = 1.632, p= 0.20]. The fact that there were no systematic
differences in environmental ratings between presentation
modalities (i.e., conditions) suggests that participants were on
the whole equally able to judge environmental quality from
audio-only and video-only stimuli as they were with movie-
stimuli. However, further analysis revealed a strongly significant
interaction between Location and Modality [F(12) = 7.56, p<2e-
13], which led us to conduct a series of post hoc analyses
with Tukey’s Honest Significant Difference test. Similarly to
the onsite study, it was found that the Garbage location was
lower rated than all the six others, corresponding to between
1.1 and 2.2 steps on the seven-step Likert scale, with a large-
sized effect of 1.37 SD (Hedges’ g with correction for different
group sizes). Furthermore, the Wetmarket was lower rated
than the five remaining locations, corresponding to between
0.44 and 1.1 scale steps, with a medium-sized effect of 0.62
SD (Hedges’ g, corrected). Lastly, the Food Court was rated
0.6 scale steps higher than Flowers and Meat, with a medium
effect of 0.53 SD (Cohen’s d) (see Table 1, Col. 4–6, and
Figure 6). The largely corresponding results between the two
studies in terms of perceived environmental quality will be
probed further below.
Smell Sources
The smellwheel response interface has ‘neutral’ at the centre
and eight main types of smell evenly distributed in cardinal
directions: Vegetable, Fruity, Floral, Medicinal, Chemical, Fishy,
Offensive, Earthy. Each of the eight types is exemplified with
several subtypes (see Figure 3). Participants could mark with
a mouse click up to three smells that they imagined in the
present environment (audio-only, video-only, or movie). They
were asked to “click at the centre (inner circle) if they imagined
the smellscape as neutral, and further out (outer circle) if they
imagined that smells would be strong”.
Participants marked on average 2.6 smells per stimulus; there
were 2907 clicks in all. They tended to be placed close to the
eight spokes of the smellwheel or at the centre. Within the
inner ‘neutral’ circle, there were 13.9% of the clicks; between
inner and mid circles, 54.8% of clicks; between mid and outer
circles, 21.8%, and outside the outer circle, 9.5%. The analysis
proceeded by interpreting smellwheel responses in terms of smell
type (discrete, eight kinds) and smell strength (continuous). In
the present analysis, the click’s distance from the centre is taken
as a proxy for the strength (perceived intensity) of the identified
type of smell, its numerical value relative to the radius of the
outer circle. For example, a smell strength value of 0.5 means
that the participant clicked half-way between the centre and the
outer circle. We observed a correlation between the order of
clicks and their distance from the centre. The mean distance
for the first clicks that participants made was 0.514, for the
second 0.505, and for the third 0.468. Analytic tests comparing
the distributions of clicks, i.e., 1st versus 2nd and 2nd versus
3rd, were significant in both cases (p<0.0001, Mann–Whitney’s
rank-based test on paired samples), however the effect sizes were
small (0.08 and 0.15 SD, respectively). This order effect can be
explained by assuming that the smell that participants imagined
to be strongest was also the first one that they clicked on, and
for ensuing smells the imagination was less certain, or weaker.
Moreover, the number of clicks could also be a useful measure
for smell source strength, as shown by the fact that distance from
centre and click count (within locations, modalities, and smell
types) were highly correlated (distance correlation dcor = 0.59,
p<0.0002 for 5,000 bootstrap replications).
Type
Figure 7 illustrates graphically (in the style of Belgiorno et al.,
2013, p. 15) the relative intensities of McGinley’s eight smell types
in the seven locations and three modalities. From inspection,
it is clear that one or two smell types were imagined to be
dominant at each of the locations, and the three modalities
were largely congruent. At the Carpark, the dominant types
were Chemical and Earthy; at Flowers and Meat and the Food
Court, Vegetable smells dominated; at Garbage, the Offensive
smells were dominant; at the Green Core mini-park, Earthy
smell types were prevalent; at the Stores, Earthy and Chemical
types; and finally at the Wetmarket, the Fishy smells were
dominant. This is very similar to the smells detected by the onsite
study participants, see Figure 5. Note also that the differences
between modalities in the online virtual smellwalk were not
striking. In the Audio-only condition, the types were more evenly
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FIGURE 6 | Boxplots of ratings (N= 53) of environmental quality in seven locations, as imagined when presented in three different audiovisual conditions. Quality
was rated on a seven-step Likert scale; see the text for details.
FIGURE 7 | Graphical illustration of smell types (qualities) and intensities in seven locations and in three modalities. Smell types are abbreviated for clarity: Veg,
vegetable; Fru, fruity; Flo, floral; Med, medicinal; Che, chemical; Fsh, fishy; Off, offensive; Ear, earthy. Colours refer to modalities, i.e., stimuli conditions. For each
smell type and modality, the coloured ring is centred on the mean distance of clicks, and its thickness and size are proportional to the number of clicks made.
distributed, but even at the Garbage location, the participants
imagined largely the same kind of smell types as they did when
video was present.
Strength
Unsurprisingly, analysis of variance revealed significant
differences of imagined smell strength between locations and
modalities. This is illustrated in Figure 8. For locations, Tukey’s
Honest Significance test showed that smell strength was higher at
the Garbage location than at any of the other six. The difference
was on average 0.17 (range 0.12. . .0.21; recall that strength
takes a value from 0 to about 1), with an overall medium-
sized effect of 0.54 SD (Hedges’ g with correction for different
group sizes). It was also significantly higher at the Wetmarket
than at Flowers and Meat or Food Court; the difference was
about 0.08 for both, with an overall effect size of 0.27 SD. For
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FIGURE 8 | Imagined smell intensity (proxied by mouse-click distance from smellwheel centre; see the text for details) in seven locations and three audiovisual
modalities.
modalities, the same test showed that imagined smell strength
was higher in the Movie condition than in the two unimodal
conditions. The difference between Movie and Audio was 0.08
(Cohen’s d= 0.27 SD), and between Movie and Video it was 0.05
(d= 0.17 SD).
Hedonic Tone
The onsite participants were asked to imagine the smells in
the represented environment (audio, video, or movie), and
describe them using their own words. There were 1113 free-
form responses (7 ×3×53), each consisting of four words
on average. They were pre-processed by removing non-letter
symbols (e.g., question marks, citations, parentheses, trailing
spaces), transcribing to lowercase, and merging grammatical
variations, e.g., singular and plural. There were a total of 2561
individual words, out of which 344 were unique. The 33 most
common were: food (6.0%), fish (4.0%), meat (3.9%), grass,
neutral (2.5%), raw (2.0%), rain (1.9%), chemical, car (1.8%),
exhaust, fresh, vegetables, air (1.6%), earthy, garbage (1.4%),
clothes (1.2%), incense, market, musty, smoke, wet (1.1%),
damp (1.0%), sweat, cooked, oil, dust, restaurant, humid, trash,
humidity, new, rubbish, blood (0.7%). The frequency counts
for each of the three modalities (audio, video, and movie) are
listed in Table 2.
A cumulative score for hedonic tone for each location and
modality was calculated from the descriptive words, in a similar
way as for the onsite free-form annotations. We matched the
344 unique words from our participants with Dravnieks’ list
(Dravnieks et al., 1984). For 27% of the unique words a perfect
match was available; for 22% a close match was found (e.g.,
iron →Metallic); for 30% an acceptable match was made by
considering the word in the context of its sentence [e.g., car →
Gasoline, solvent, or food →Seasoning (for meat)]. For 20% of
the words no match could be made (e.g., air, clothes, house). This
process yielded a hedonic score for each participant’s free-form
annotations of smell sources. Scores were accumulated across
participants to give an estimate for the hedonic tone of each of
the seven locations and three modalities. The distributions are
illustrated in Figure 9.
Analysis of variance (ANOVA) revealed that there were
differences between the locations. Post hoc analysis with
Tukey’s Honest Significant Difference test showed that the
Garbage location was lower rated lower than all the six
others, corresponding to between 2.9 and 4.7 units (Dravnieks’
scale values, accumulated within each participant’s free-form
response), with a large-sized overall effect of 1.47 SD (Hedges’
g with correction for different group sizes). Furthermore, when
Garbage was removed from the data, the Wetmarket location was
lower rated than the five remaining, corresponding to between
0.54 and 1.8 units, with a medium-sized overall effect of 0.50 SD
(Hedges’ g, corrected). Tukey’s test also revealed that Carpark
had lower hedonic tone than Food Court and Flowers and Meat,
and that Stores was lower than Flowers and Meat, Food Court,
and Green Core, though these differences will not be discussed
further. Note that there were no systematic differences in hedonic
tone between the three conditions of stimulus presentation.
As was already noted in the analysis of onsite data, some
online responses that were frequent (and therefore probably
important) could not be satisfactorily matched to Dravnieks’ list.
For example, the matchings with food-related or rain-related
descriptions were only acceptable, and no matching could be
made for the relatively frequent descriptions involving [fresh] air
or [new] clothes. Furthermore, only 69 of the 141 items were used
at all; more than half were not relevant to the present study. This
suggests that the overlap is not large between the smells (both real
and imagined) perceived at a South-East Asian outdoor market
and the smells in Dravnieks’ study from almost 40 years ago
in Illinois, United States. Future research might pursue a cross-
cultural approach to smellscape perception and the categorisation
of smell sources.
Comparison and Summary of Results
Finally we analyse the results from the two studies together and
compare them in terms of environmental quality, hedonic tone,
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TABLE 2 | Most common descriptors for annotations of imagined smells (N= 53) at seven locations in three modes of presentation.
Audio Video Movie
Carpark Neutral (9.4%), car (4.7%), chemical,
rain, Air conditioning (3.5%), factory
(3.5%)
Grass (14.0%), rain (13.0%), air (8.1%), exhaust
(5.9%), car (5.2%), fresh, wet (3.7%), petrol
(3.0%), after (2.2%), concrete, dust, open
(2.2%)
Grass (15.0%), exhaust (9.8%), car (9.1%), rain, air
(4.2%), earthy (3.5%), petrol, after (2.8%), dust
(2.1%), fresh, pollution, smoke (2.1%)
Flowers and Meat Food (11.0%), neutral, fish (4.5%),
cooking (3.4%), meat (3.4%)
Food (9.4%), neutral (8.3%), coffee (3.1%),
cooked, dust, people, sweat (3.1%)
Meat (19.0%), vegetables (18.0%), raw (10.0%),
fish (7.4%), grass (3.7%), market, blood (2.9%),
fresh, fruit, earthy (2.2%), food, wetmarket (2.2%)
Food Court Food (20.0%), restaurant (6.9%),
cooked (5.2%), neutral, tea (3.4%), air
(2.6%), people (2.6%)
Food (18.0%), crowd (5.4%), restaurant, neutral
(4.5%), cooked (3.6%), people (2.7%), sweat
(2.7%)
Food (31.0%), cooked (4.6%), oil, garlic (3.8%), oily,
cooking (3.1%), hawker (2.3%)
Garbage Chemical (7.7%), water (4.6%), metal
(3.8%), metallic, factory (3.1%), wood,
carwash (2.3%), dirty, garbage,
machinery, oil, smell, soap, trash (2.3%)
Garbage (13.0%), rubbish (7.1%), trash, rotten
(6.2%), pungent (4.4%), putrid, bad (2.7%),
chemical, rancid, sour (2.7%)
Garbage (12.0%), trash (6.8%), food (5.3%), putrid
(4.5%), rotten, rubbish (3.8%), pungent (3.0%),
sewer, fish (2.3%), offensive, rancid, rotting, sour,
wet (2.3%)
Green Core Meat (9.9%), food (9.0%), neutral
(6.3%), raw (4.5%), restaurant (3.6%),
smoke (2.7%)
Grass (21.0%), fresh (8.7%), meat (7.1%), fish
(6.3%), earthy (4.0%), wet, air (2.4%), market,
rain, raw, vegetables (2.4%)
Grass (19.0%), meat (9.5%), earthy (6.3%), raw, fish
(4.8%), fresh, air (4.0%), food (3.2%), damp (2.4%),
greenery, humid, market, wet (2.4%)
Stores Car (7.9%), exhaust (7.1%), incense,
smoke, fumes (3.6%), traffic, medicinal
(2.1%), medicine, neutral, street, sweat
(2.1%)
Clothes (11.0%), incense (6.9%), new, musty
(5.5%), rain, chemical (4.8%), fabric, dust
(2.8%), medicinal, air (2.1%), clothing, earthy,
floral, humid (2.1%)
Clothes (11.0%), incense (8.1%), new (6.1%),
chemical (5.4%), car (4.7%), musty, exhaust (4.1%),
fabric (3.4%), floral, plastic (2.7%), Chinese (2.0%),
medicinal, shop, smoke (2.0%)
Wetmarket Meat (12.0%), food (7.9%), fish (4.0%),
market, raw, sweat (3.2%), vegetables,
blood (2.4%), fruit, hawker, neutral,
people (2.4%)
Meat (14.0%), fish (10.0%), food (9.3%), market
(5.1%), raw, sweat (4.2%), vegetables, butcher
(2.5%), cooked, dust, wetmarket (2.5%)
Fish (45.0%), raw (5.8%), meat (4.9%), damp
(2.9%), dead, humid, market (2.9%)
The listed descriptors are those that occurred three times or more in each of the 21 stimuli.
and smell sources. The onsite study represents the ‘ground truth’,
in the sense that the olfactory environment was physically present
to the participants even if they might not have been fully able to
identify or label the smell sources. In the online study no smell
variations existed physically, so all differences in annotations and
ratings of smells were imaginary, and evoked by the audiovisual
stimuli. Hence, it is of interest to compare results from the two,
for those variables that are comparable. In what follows, we report
results using Canonical Correlation Analysis (CCA) to compare
ratings of environmental quality, and estimates of hedonic tone
of the smellscape as constituted by smell sources, respectively.
For these multivariate measures results from the two studies are
available in numeric form (see Table 1). CCA is a dimensionality
reduction technique that takes two datasets – matrices with
an arbitrary number of columns (variables) – and finds the
projection that accounts for the most of the covariance between
the two (Thompson, 2000; for an application, see e.g., Eerola
and Vuoskoski, 2011). Lastly, we make a summary qualitative
comparison based on free-form annotations.
Environmental Quality
A comparison between Figures 4 and 6suggests that an
association exists between the two studies, in terms of ratings of
environmental quality. We ask the Reader to bear in mind that
the sonic, visual, and olfactory aspects of the real, multimodal
environment and rated during the sensory walk, do not directly
correspond to the audio, video, and movie representation
modalities that were presented online as a ‘virtual sensory walk’.
Moreover, in the online situation, participants were asked to
make an overall evaluation of how pleasant the environment was
imagined to be; they were not specifically required to imagine the
olfactory environment. This, as we shall demonstrate, becomes
important for how to interpret the results.
First, we use CCA to measure the overall association between
the means of onsite overall quality ratings in three environmental
aspects and the means of online pleasantness ratings in three
presentation modalities (Col. 1–3 vs. Col. 4–6 in Table 1).
The observed correlation between the first canonical variates
from the two matrices is 0.99912. A p-value can be simulated
by creating a distribution of correlations between two random
matrices of the same sizes (both 7 ×3), over 50,000 repetitions.
Using this bootstrap method, the simulated p-value is 0.107;
this means that a spurious correlation as high as the one
observed occurs 10.7% of the time. Thereby the data do not
support inferring that the two situations are comparable in
terms of the ratings for environmental quality. However, we can
exclude the onsite olfactory ratings and calculate the measure
of association between onsite sonic and visual aspects with the
three audiovisual online conditions (Col. 1–2 vs. Col. 4–6 in
Table 1). The first canonical correlation component is then
0.99869. The bootstrap distribution in this case is created on
random matrices of different sizes (2 ×7 and 3 ×7), producing
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FIGURE 9 | Boxplots of cumulative hedonic scores for seven locations and three modalities, estimated from free-form descriptions of imagined smells by raters
(N= 53) matched against previous data (Dravnieks et al., 1984).
a simulated p-value of 0.0074. This is highly significant, and
means that a spurious correlation as high as the one observed
occurs only 0.7% of the time. Moreover, similarly testing the
association between onsite olfactory aspects on its own with
the three audiovisual online conditions (Col. 3 vs. Col. 4–6 in
Table 1), yields a canonical correlation of 0.82494. The bootstrap
distribution created on random matrices (1 ×7 and 3 ×7)
yields a p-value of 0.28, which is clearly non-significant. These
results show that while information about the quality of the
sonic and visual environment is transferable from an onsite,
real situation to an online, virtual situation, this is not the case
for olfactory information. In our study, the online task did not
specifically require participants to imagine the smellscape, and
the onsite information about the olfactory environment was not
spontaneously evoked and reconstituted through the audiovisual
information alone.
Hedonic Tone
We run the same analysis between means of onsite hedonic
scores and means of online hedonic scores in three presentation
modalities (Col. 7 vs. Col. 8–10 in Table 1). Note that this
comparison does not involve data from McGinley’s smell wheel,
used in the online study, but only the free-form annotations
which had been gathered in exactly the same way in both
studies, onsite and online. The scores for hedonic tone were
estimated via Dravniek’s list (Dravnieks et al., 1984). The
observed first canonical correlation is 0.98486. The bootstrap
distribution in this case is created on random matrices (1 ×7
and 3 ×7), producing a simulated p-value of 0.0086. This is
highly significant, and means that a spurious correlation as high
as the one observed occurs only 0.86% of the time. In terms of
hedonic tone, an association between the two studies is supported
by data. Nevertheless, the critical Reader will want to take into
account that the estimates for both sets of data were based on
Dravnieks’ study, which may or may not be ideal for the smells in
the present situation.
Smell Sources
For smell source types and strengths, we interpret the onsite and
online results with a qualitative approach without attempting
to make strong conclusions. The real, onsite smell sources were
distilled from free-form verbal annotations of source categories
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Lindborg and Liew Real and Imagined Smellscapes
(Figure 5), while the imagined, online smell sources were those
most frequently indicated by the smellwheel responses (Table 2).
•Carpark: Across onsite and online situations, descriptions
typically refer to grass, cars, car exhaust, and rain. Note the
mention of air conditioning in the audio-only condition
(noticeable in the recording), through which wafts of smells
from the food court on the level below came through.
•Flowers and Meat: The onsite descriptions highlight the
mix of smells from flowers, vegetables, and raw meat.
Meanwhile, online descriptions do not pick up on the
flowers, and emphasise food-related smells, also in the
audio-only condition.
•Food Court: In both situations descriptions of food smells
abound. Onsite participants also identified foul smells that
were not imagined by online participants. In the latter
case, mentions of people were fairly common in audio and
video conditions.
•Garbage: Here, descriptions onsite and in online video
and movie conditions were dominated by words such as
trash, pungent, and rotten foods. In the online audio-
only condition, the more common words were about
chemicals, water, metal, and machinery, and participants
appear to have imagined a factory or carwash rather than a
garbage handling area.
•Green Core: Onsite descriptions mix food smells and grass,
which were also highlighted in the online descriptions
in video and movie conditions. The presence of smells
from grass, trees, and soil was not imagined in the audio-
only condition.
•Stores: The smell of incense paper is annotated as dominant
onsite. This was echoed in the online descriptions in
all three conditions, which also imagine smells from car
[exhaust]. The audio condition did not evoke the smell of
clothes, which are clearly visible in the video (and movie)
and are the most frequently described.
•Wetmarket: The smell of fish is clearly dominant onsite,
and it is imagined in all three online conditions, although
the audio-only condition evoked more general terms such
as meat and food more frequently than the specific fish
association.
In summary, smell source descriptions were in fairly high
agreement between onsite and each of the three online
conditions for the Carpark, Food Court, Stores, and Wetmarket
locations. Notably, the audio-only condition in the online study
failed to evoke significant smell imaginations for the Green
Core and Stores locations, and most pertinently, the Garbage
location did not contain sounds that triggered smell associations
in this direction.
DISCUSSION
The olfactory system (in the brain) is closely connected to the
limbic system, involving neural regions like the hippocampus,
amygdala, and thalamus (Hedblom et al., 2019). Consequently,
olfactory perception is also closely tied to emotional and stress
processing, and smell-related autobiographical memories with
associated emotional encodings are also retrieved with stronger
activation of the amygdala, beyond non-emotional memories or
emotional memories associated with other modalities (Gottfried
et al., 2004;Herz, 2016). Consistently, perceived smells that
are not actively attended to are also able to evoke emotional
responses in individuals (Haviland-Jones and Wilson, 2010,
p. 237). Smells can be incorporated into individuals’ schema
for places (Tse et al., 2007;Henshaw et al., 2009), with
strong connotations with affective and emotional associations.
However, despite these emotional linkages, certain behavioural
fight-or-flight decisions are often not concluded solely based
on olfactory perception. Instead, smells appear to trigger a
search for contextual meaning, or confirmation of the odour
source, through other (visual or auditory) modalities (particularly
for fear-related odours; Haviland-Jones and Wilson, 2010,
p. 242), possibly in a bid to match or form new associations
from long-term memory. If so, this suggests that cross-modal
information is important to olfactory perception. This forms
an angle to interpret our current results: we would expect to
see systematic differences when people are asked to imagine
smells when exposed to either sound- or visuals-only stimuli, or
audiovisual (i.e., movie stimuli). Indeed, the highly significant
association in terms of hedonic tone (pleasantness) between
the online and onsite situations in our data suggests that
when online participants were specifically required to imagine
smells from audiovisual information, they were successful.
They could approximate the types of onsite smell sources and
their ‘actual’ perceived hedonic tone. Imagined smells may
thus be a mechanism towards the emotional evaluation of
audiovisual environments. By contrast, the analytical results in
this study show that ratings of the quality of the olfactory
environment (immediately available to onsite participants) did
not translate to ratings of environmental quality from audiovisual
information only (with no olfactory stimuli present) at least when
online participants were not required to imagine smells from
audiovisual information.
We may consider the difference between perception and
cognition more broadly, and how it might apply in the case
of the present study. What does it mean to say that someone
has the smell of a fish ‘in the nose’, or that she has a mental
representation of fish smells ‘in the brain’? Zach et al. (2018)
conducted a study on olfactory, auditory, and visual volitional
memory recall of French Fries among a group of mainly
teenagers. They found that on-demand olfactory recall was at
least to some extent possible for a majority of their subjects
(73.2%, 71.0%, and 77.4% in their three groups, respectively).
Levels were similar to those for auditory recall but much lower
than those for visual recall. However, Zach also states that
olfactory recall was harder to do for their subjects, perhaps
because smells might take longer time to evoke by volition
than sounds or sights. On the other hand, Young (2020) points
out that imagination is a broader concept than memory recall:
“olfactory imagery seems limited when only considered as the
capacity to voluntarily self-generate an experience of olfactory
quality in the absence of sensory stimulation. However, a
more liberal conception including any experience of olfactory
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quality in the absence of sensory stimulation widely expands
the instances of olfactory imagery by including dream states,
hallucinations, autobiographical odour memories, and olfactory
memories” (Young, 2020, pp. 3305–3306). In the subjective, free-
form annotations in our present work, the evidence of type and
strength of olfactory recall – imagining smell on demand and in
the absence of stimulation by actual odours – is always going
to be reported with different levels of vividness, both because
olfactory imagination can be expected to vary greatly across the
population, but also because of individual factors unrelated to
olfaction (e.g., language abilities, attentiveness). Future research
might attempt to validate self-evoked smell percepts through
behavioural, physiological, and other external measurements.
This reiterates the difficulty of spontaneously imagining smells to
match audiovisual environments, since individuals often have to
draw on their own familiar (culturally rooted) experiences to do
so (Bruce et al., 2015). Referring to fear-odours, (Haviland-Jones
and Wilson, 2010, p. 242) noted that “sensing an odour without
having a visual or auditory match leads to a slow, cautious search
for a match rather than the rapid fear-flight response”. This led
the authors to propose that “there must be an ongoing, not-quite-
conscious match-mismatch system that is correlating bits of
information across the sensory systems. It is actively searching for
existing associations and making new associations” (Haviland-
Jones and Wilson, 2010, p. 245). If such a mechanism exists, we
would expect to see systematic differences when people are asked
to imagine smells when exposed to either sound- or visuals-only
stimuli, or audiovisual (i.e., movie stimuli).
To a certain extent, the significant relationship identified
between onsite and online participants in hedonic tone could
be facilitated by a shared cultural background (similar schema
towards the market). However, in real-world settings, one
cannot always control the cultural backgrounds of viewers to a
particular video. Given that olfactory perception has a stronger
impact on stress reduction and other health-related paradigms
(Annerstedt et al., 2013;Hedblom et al., 2019), this may lead to
a cultural imbalance in the subjective evaluation of environments
(such as through movies or online videos) that present only
audio-visual information. Individuals may form incomplete
or biased judgements about a location or environment of
another (unfamiliar) culture, if presented solely with audiovisual
information (e.g., a trailer to an exotic travel destination). This
may in turn have implications on tourism strategies in general
for a city or country (Henshaw et al., 2016;Spence, 2020, p. 8).
The recent study by Flavián et al. (2021) provides evidence that
congruent smell presentation as part of a multimodal VR display
acts to increase positive behavioural responses in the context of
‘virtual tourism’. We refer the interested Reader to their article
which also contains an excellent review of recent development in
olfactory-extended virtual reality (Flavián et al., 2021).
This issue of schema, memory and association in imagining
smells is evident in the discrepancy of descriptions between
locations in the study. For example, some locations, such as
the Carpark, that were less subject to cross cultural specificity,
appeared to have more qualitative consistency between onsite
descriptions and online imaginations. By contrast, the onsite
descriptions of the Wetmarket frequently featured fish-related
smells, as opposed to the imagined meat-related smells that were
prevalent in imagined online descriptions. One explanation for
this discrepancy could be in the direction of attention. The
auditory/visual stimuli forces the viewer to follow a top-down
specified path of attention for smell-imaginations, which can be
influenced by one’s upbringing and culture (Masuda et al., 2020).
On the other hand, given the source-confirmation drive often
associated with olfactory perception, onsite participants could
have first relied on olfactory perception as a preliminary input,
before searching for the source through audiovisual confirmation
in a bottom-up approach.
LIMITATIONS AND FUTURE WORK
The current findings are limited in that no olfactory stimuli were
presented during the online study. The article by Flavián et al.
(2021) is exemplary in its design of an experiment with olfactory
conditions when a small number of distinct smells are tested.
It is inspiring for our further work on the relationship between
real smellscapes (‘in the nose’) and imagined smellscapes (‘in
the head’), which will be needed in order to test the findings
we have reported here. A further limitation is the substantial
time gap between conducting the onsite study at Tiong Bahru
market, and the online study. We had hoped to carry out a
confirmatory second onsite study, in the form of a sensory walk,
but unfortunately the COVID-19 restrictions during the summer
of 2021 made it impossible. Outlets at the market were closed or
working at minimal capacity; e.g., no customers were allowed to
sit at food court tables, and no gatherings of people were allowed
anywhere. Waiting for restrictions in Singapore to be lifted would
delay publication of the present text. Instead, we are turning our
energies towards a follow-up project in Hong Kong (where the
first author is currently based). It will include a survey of several
wet markets, with collection of audio-visual recordings and
olfactory measurements together with observations made during
sensory walks. An interesting option for an onsite study might
be to partially inhibit multisensorial perception, for example
by blindfolding some participants, having others wear hearing
muffs, and others again with nose clips. Experiments in the
laboratory will include a suitable way of replicating the relevant
smells of wet markets, for example by presenting olfactory stimuli
corresponding to the main parts of the smellwheel (McGinley and
McGinley, 2002) by using odour compounds in ceramic vessels or
on perfume sticks.
Future work will also pay close attention to different kinds
of memory. For example, when asked to imagine smells
on demand, the memory one recalls might be semantic
(“knowing”; common knowledge shared by others) rather than
episodic (“remembering”; a person’s autobiographical olfactory
experiences). For example, when asked the question “In your
own words, describe the smells that you imagine”, a participant
who has never been to a wet market might still be able to
write down words like “fishy”, “seafood”, and so forth, simply
using knowledge they learned in school. In our present online
study we enrolled participants from Singapore and neighbouring
countries in South-East Asia, allowing the assumption of them
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having personal experience with Asian-style open air markets.
However, it is a limitation of our data elicitation method that it
did not make a clear distinction between episodic and semantic
memories. In future online studies, it might be of interest to
include a ‘no external stimulus’ condition where participants are
required, for example, to recall the last time they were in the
specified environment and to describe the smells they imagine
based on their lived experience.
CONCLUSION
Analysing perceptions of the built environments, Jean-Paul
Thibaud wrote that “urban ambiances are created and
experienced as a product of different, sometimes unique,
blends of sights, sounds, smells, textures, tastes and thermal
conditions” (Thibaud, 1995, p. 204). Smell represents an
important dimension of our understanding and design of the
everyday environment. In particular, the olfactory environment
offers benefits for well-being and restoration both in architecture
(Spence, 2020, pp. 6–7) and in the context of calm, green, natural
places (Hedblom et al., 2019). To be of optimal usefulness
for urban design, research on smellscape perception should
consider the olfactory environment in relation to individual
factors (Lindborg and Friberg, 2016;Xiao et al., 2018). The urban
smellscape indeed forms part of our intangible heritage (Lenzi
et al., 2021). It is valuable as culture, and at the same time, it
also represents a marketing opportunity (Henshaw et al., 2016),
especially for urban servicescapes that contain a multitude of
sensorial information (Bruce et al., 2015,p.6;Lindborg, 2015).
Recent interdisciplinary initiatives show the way towards a
‘World Smellscape Project’ based on the model of soundscape
research (Schafer, 1977). Smellscape measurements and
descriptions made by ‘nose-witnesses’ (Porteous, 1985, p. 360)
constitute an archive of experiential descriptions of various
smells around the globe. Notably, the Odeuropa project2,
which is involved in intangible cultural heritage and everyday
culture, aligns with our present work. Meanwhile, D-Noses3
focuses on odour pollution control, and GoodCityLife4works
at improving the urban living environment through parallel
smart-city mapping projects. The citizen science approach also
doubles up as a resource for the historical archival of locations
and places as they develop over time. Through this paper, we
present a humble contribution to this larger discourse through
a documentation of the smellscape of an area of significance
in Singapore’s history, while examining cross-modal linkages
between olfactory perception and audio-visual perception.
DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
2https://odeuropa.eu/
3https://dnoses.eu/
4https://goodcitylife.org/
ETHICS STATEMENT
The studies involving human participants were reviewed
and approved by Institutional Review Board of Nanyang
Technological University #IRB-2015-10-056, and Ethics
Committee of City University of Hong Kong #13-2020-08-E. The
patients/participants provided their written informed consent to
participate in this study.
AUTHOR CONTRIBUTIONS
PL conceived the study and conducted the analysis.
KL and PL collected the onsite response data and PL
collected the online data. Both authors collaborated on
writing and reviewing all parts of the manuscript. Both
authors contributed to the article and approved the
submitted version.
FUNDING
The study received funding support through a StartUp Grant to
PL, #7200671 City University of Hong Kong.
ACKNOWLEDGMENTS
We thank Ute Meta Bauer and Magdalena Mageira for producing
the Tiong Bahru Sensory Walk as part of “Incomplete City
Walks”, and Julia Mihàly for assistance at the event. We
acknowledge valuable contributions to the manuscript, in
particular the “Discussion” and succeeding sections, by the
reviewers and graduate student Yingshi Feng, while hasting
to state that any remaining errors or shortcomings in the
text are entirely the responsibility of the authors. Methods
for onsite data collection were approved by the Institutional
Review Board of Nanyang Technological University #IRB-
2015-10-056, and online data collection was funded by Start-
Up Grant #7200671 from City University of Hong Kong
to PL, with procedures receiving Ethics Committee approval
#13-2020-08-E.
SUPPLEMENTARY MATERIAL
The Supplementary Material for this article can be found online
at: https://www.frontiersin.org/articles/10.3389/fpsyg.2021.
718172/full#supplementary-material
Supplementary Data Sheet 1 | Sample page of the protocol used in the
onsite sensory walk.
Supplementary Data Sheet 2 | Collected raw data from Study 1, onsite
(CSV).
Supplementary Data Sheet 3 | Collected raw data from Study 2, online (CSV).
Supplementary Data Sheet 4 | Code example (R script) for retrieving and
pre-processing of the raw data.
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Conflict of Interest: The authors declare that the research was conducted in the
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Frontiers in Psychology | www.frontiersin.org 19 December 2021 | Volume 12 | Article 718172