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It is well established that composite facial images are perceived as more attractive compared with individual images, suggesting a preference for heterozygosity. Similarly, there is evidence that preferences for body odours might be linked to heterozygosity. Here, we tested whether blending individual body odours into composites would follow a similar pattern as observed in the perception of faces. We collected axillary odour samples from 38 individuals, which were subsequently assessed individually and as composites of two (N = 19) or four (N = 9) body odours regarding their pleasantness, attractiveness and intensity. We found no significant differences between mean ratings of individual odour samples or composites of two or four odour samples. Our results indicate that, in contrast to faces, composite body odours are not rated as more attractive. Composite body odours retain similar hedonic perceptual qualities as individual odours, thus highlighting differences in visual and chemosensory perceptual mechanisms.
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Article
Human Body Odour
Composites Are Not
Perceived More Positively
than the Individual Samples
Jitka Fialova
´
Faculty of Science, Charles University, Prague, Czech Republic; National
Institute of Mental Health, Klecany, Czech Republic
Agnieszka Sorokowska
Institute of Psychology, University of Wroclaw, Poland; Smell & Taste
Clinic, Department of Otorhinolaryngology, TU Dresden, Germany
S. Craig Roberts
School of Natural Sciences, University of Stirling, UK
Lydie Kubicova
´
Faculty of Humanities, Charles University, Prague, Czech Republic
Jan Havlı
´c
ˇek
Faculty of Science, Charles University, Prague, Czech Republic; National
Institute of Mental Health, Klecany, Czech Republic
Abstract
It is well established that composite facial images are perceived as more attractive compared with
individual images, suggesting a preference for heterozygosity. Similarly, there is evidence that
preferences for body odours might be linked to heterozygosity. Here, we tested whether
blending individual body odours into composites would follow a similar pattern as observed in
the perception of faces. We collected axillary odour samples from 38 individuals, which were
subsequently assessed individually and as composites of two (N¼19) or four (N¼9) body odours
regarding their pleasantness, attractiveness and intensity. We found no significant differences
between mean ratings of individual odour samples or composites of two or four odour
samples. Our results indicate that, in contrast to faces, composite body odours are not rated
as more attractive. Composite body odours retain similar hedonic perceptual qualities as individual
odours, thus highlighting differences in visual and chemosensory perceptual mechanisms.
Corresponding author:
Jitka Fialova
´, Faculty of Science, Charles University, Vinic
ˇna
´7, 128 44 Prague, Czech Republic.
Email: jitka.fialova@natur.cuni.cz
Creative Commons CC BY: This article is distributed under the terms of the Creative Commons Attribution 4.0 License
(http://www.creativecommons.org/licenses/by/4.0/) which permits any use, reproduction and distribution of the work without
further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sage-
pub.com/en-us/nam/open-access-at-sage).
i-Perception
2018 Vol. 9(3), 1–15
!The Author(s) 2018
DOI: 10.1177/2041669518766367
journals.sagepub.com/home/ipe
Keywords
heterozygosity, averageness, odour blend, olfaction, MHC, mate preferences
Date received: 17 May 2017; accepted: 26 February 2018
Introduction
A robust body of evidence indicates that composite facial images are perceived as more
attractive compared with the mean attractiveness rating of their constituent images. The
phenomenon was first noted by Galton (1879) who used photographic superimposing
techniques to combine facial images. More recent studies have improved upon these
techniques, using computer graphics to generate composite facial images (Grammer &
Thornhill, 1994; Langlois, Roggman, & Musselman, 1994; Rhodes, Sumich, & Byatt, 1999;
Rhodes & Tremewan, 1996), and finding that composites are considered more attractive than
almost all constituent faces. Furthermore, there is generally a positive association between
the number of individual images constituting a composite image and its attractiveness and
averageness ratings (Langlois & Roggman, 1990), although average faces may not be the
most attractive (Perrett, May, & Yoshikawa, 1994).
The attractiveness of average faces may result from two different mechanisms. First, it
might be a by-product of visual system processing by which average faces can be processed
faster because they resemble a mental representation of a prototypical face (Enquist & Arak,
1994). Indeed, it appears that prototypes are processed faster and have a higher probability of
recognition (Posner & Keele, 1968; Smith, Shoben, & Rips, 1974), and visual processing is
more fluent as reflected in decreased activity in the posterior occipital cortex (Aizenstein
et al., 2000). In addition, there is a positive relationship between prototypicality and
preference, consistent with the observation that an increase in processing fluency also
increases liking (Martindale & Moore, 1988; Whitfield & Slatter, 1979). An alternative
explanation proposes that facial averageness might be a marker of heterozygosity (i.e.,
genetic diversity at certain loci; Lie, Rhodes, & Simmons, 2008; Thornhill & Gangestad,
1993). It has therefore been argued that attractiveness of average faces might be a
perceptual adaptation to favour heterozygous individuals (Thornhill & Gangestad, 1993).
Heterozygosity in some loci positively affects viability of the organism, as deleterious
alleles are predominantly expressed in recessive fashion (i.e., only in homozygotes).
Further, benefits of mating with heterozygous individuals may include reduced risk of
disease transmission and potential for high-quality paternal care (Kirkpatrick & Ryan,
1991; Roberts et al., 2005).
Facial attractiveness and averageness is associated with heterozygosity in the genes of the
major histocompatibility complex (MHC; Lie et al., 2008; Roberts et al., 2005). The MHC
complex appears to be involved in mate selection processes of various vertebrate species
including humans (Kamiya, O’Dwyer, Westerdahl, Senior, & Nakagawa, 2014; Winternitz,
Abbate, Huchard, Havlı
´c
ˇek, & Garamszegi, 2017). MHC genes are extremely polymorphic
and code for cell-surface peptides that are responsible for recognition of foreign antigens and
thereby initiating an immune response. As the MHC is expressed codominantly,
heterozygous individuals are able to present a broader spectrum of peptides and thus
provide resistance to a wider range of pathogens compared with MHC homozygotes
(Havlı
´c
ˇek & Roberts, 2009). Consistent with this, MHC heterozygotes have faces that
appear more healthy (Roberts et al., 2005). There is also some evidence showing
preferences for body odour of MHC heterozygotes: Male body odour attractiveness as
2i-Perception 9(3)
rated by women was positively associated with MHC heterozygosity, but there was no similar
pattern when men rated female body odour samples (Thornhill et al., 2003).
Based on this evidence, one may speculate whether composite body odours might
perceptually mimic odours of heterozygote individuals, as has been observed in studies of
composite faces. If so, one would predict that body odour composites—individual odours
blended and presented together—would be rated more positively than the individual samples.
A test of this prediction could have important consequences for the methodology of body
odour studies. Numerous previous studies have presented composite odours to assessors to
test potential communicatory significance of body odours. They use composite odours in an
attempt to achieve a representative odour sample associated with a particular characteristic
or state of interest while reducing the importance of individual variability in odour profiles.
Thus, the rationale behind these studies is that composite body odours (usually created by
pooling odour samples from people with a given characteristic) will contain shared qualities
based on their group attributes, such as gender (Lu
¨bke et al., 2014; Mutic, Moellers,
Wiesmann, & Freiherr, 2016) and sexual orientation (Martins et al., 2005). Similarly,
composite body odours have been used for testing various affective states such as
happiness and fear (Chen & Haviland-Jones, 2000), disgust (de Groot, Smeets, Kaldewaij,
Duijndam, & Semin, 2012), sadness (Gelstein et al., 2011), anxiety (Haegler et al., 2010;
Pause, Adolph, Prehn-Kristensen, & Ferstl, 2009; Pause, Lu
¨bke, Laudien, & Ferstl, 2010;
Pause, Ohrt, Prehn, & Ferstl, 2004; Prehn-Kristensen et al., 2009; Zernecke et al., 2011), and
stress (Dalton, Maute
´, Jae
´n, & Wilson, 2013; Mujica-Parodi et al., 2009; Prehn, Ohrt, Sojka,
Ferstl, & Pause, 2006; Radulescu & Mujica-Parodi, 2013). While the approach used in such
studies is potentially very useful, it is currently unknown whether creating such composites
might influence hedonic qualities.
In light of this, here we aimed to test the effects of composite odour creation on the
perception of odour attractiveness, pleasantness and intensity. We created odour composites
comprising two and four individual odours and tested whether these composite body odours
are rated more positively compared with the distinct odours from the same individuals.
Methods
Raters
The individual samples were assessed by 110 raters (56 men, mean age 24.1 years, range 18–
34; 54 women, mean age 23.4, range 19–35) as part of previously reported studies (Fialova
´&
Havlı
´c
ˇek, 2012; Fialova
´, Roberts, & Havlı
´c
ˇek, 2016). The composite samples were assessed
by 98 raters (50 men, mean age 23.9, range 19–33; 48 women, mean age 22.8, range 19–35).
The two sets of raters were independent—no rater assessed both individual and composites.
The raters were mostly Charles University students and were contacted via e-mail, posters or
by oral invitation. Raters reported no respiratory or other diseases at the time of the study or
any problems or medication that could influence their olfactory abilities. All women were
using hormonal contraception to avoid changes in olfactory perception during the menstrual
cycle (Martinec Nova
´kova
´, Havlı
´c
ˇek, & Roberts, 2014). Following the procedure used in
previous studies, we assumed no systematic fluctuation in olfactory ability over time due to
hormonal contraceptive use, and thus scheduling of assessments was unrestricted (e.g.,
Fialova
´et al., 2016; Kohoutova
´, Rubes
ˇova
´, & Havlı
´c
ˇek, 2011; Sobotkova
´, Fialova
´,
Roberts, & Havlı
´c
ˇek, 2017). Raters received 100 CZK (approximately US$5) as
compensation for their time.
The study was conducted according to the guidelines laid down in the Declaration of
Helsinki, and all procedures involving human subjects were approved by the institutional
Fialova
´et al. 3
review board of Charles University, Faculty of Science. Written informed consent was
obtained from all participants.
Odour Stimuli
Twenty-six men (mean age 25.2 years; range 18–34) and 12 women (mean age 22.4; range 20–
26), mostly students at Charles University (Prague, Czech Republic), participated as odour
donors (sample size varies across men and women because the participants were originally
recruited for the purpose of two other studies). All donors were nonsmokers and reported no
dermatological or other diseases at the time of the study. No men shaved their armpits, while
all women shaved their armpits; axillary shaving was kept constant within sex as it might
affect perceived quality of the axillary odour (Kohoutova
´et al., 2011). All women used
hormonal contraception to avoid possible body odour quality fluctuations across the
menstrual cycle (Havlı
´c
ˇek, Dvor
ˇa
´kova
´, Bartos
ˇ, & Flegr, 2006; Kuukasjarvi et al., 2004).
Male and female donors were given 400 CZK (approximately US$20) and 1,000 CZK
(approximately US$40), respectively, in compensation for their time and potential
inconvenience caused by the prescribed diet and according to duration of the study and its
demands.
The odour donors were asked to avoid consuming smelly and spicy food, alcohol, smoking
or using any cosmetics on the day before and during the sampling day (48 hr overall). They
attached 100% cotton pads under each armpit using surgical tape and wore the pads for 12 h
overnight (see Havlı
´c
ˇek, Lenochova
´, Oberzaucher, Grammer, & Roberts, 2011). To avoid
odour contamination from extrinsic ambient odours, the donors were asked to wear as the
first layer of clothing a new white 100% cotton T-shirt that had been previously washed
without washing powder. In the morning, they placed the pads in ziplock plastic bags and
returned them to the experimenters. The samples were immediately placed in a freezer at
21C to prevent further microbial action and possible changes in odour quality. Freezing
has been shown to have no significant effect on hedonic ratings (Lenochova, Roberts, &
Havlicek, 2008). Time elapsed between removing the pads and onset of freezing was
approximately 1 to 2 hr. Each donor’s conformity with the instructions was checked by a
questionnaire, and no violations on the day of sampling were recorded.
To create composite body odours, we first ranked the individual samples of either sex based
on their attractiveness ratings. Male and female composite odours were then created by
blending two or four individual samples. We used previously unused pads that had been
collected at the same time from each individual; to do this, we used the pads collected from
the other armpit than the one that had been used for previous ratings of the individual samples.
Each pad was cut into half and pooled with halved pads from other same-sex individuals who
lay adjacent along the attractiveness continuum. In this way, we obtained 19 composites
comprised of 2 individual samples and 9 composites comprised of 4 individual samples.
Odour Rating Procedure
Ratings took place in a quiet, ventilated room. The samples from one randomly chosen
armpit of each odour donor were assessed individually, by the first set of raters. The
second set of raters assessed the composites, originating from the other armpit and pooled
as described earlier. Both kinds of samples were presented in 250 ml opaque jars labelled with
a code. Participants were asked to sniff each jar; ratings were recorded immediately after
sniffing each stimulus, but the time spent sniffing was not restricted. To avoid adaptation, the
samples were randomly split into subsets, and raters were given approximately 10 min break
4i-Perception 9(3)
between assessing each set. All samples were thawed before the rating session and then
assessed in a randomized order regarding their (a) pleasantness, (b) attractiveness and (c)
intensity, each on a 7-point scale. Both ends of each scale were verbally anchored by
descriptors (e.g., very unpleasant and very pleasant). If raters found any of the samples too
weak to assess, they could select an option ‘‘I cannot smell the sample’’ instead of rating using
the scales (this occurred for 4.9% of the individual samples, 3.4% of the two-composite body
odour samples, and 4% of the four-composite body odour samples). Such instances were not
included in analyses, and hence the sample sizes of analyses can vary.
Statistical Analysis
Kolmogorov–Smirnov tests showed normal data distribution for all dependent variables. We
computed mean values from the ratings of the individual samples that were used for creating
composite body odour samples and compared them with actual ratings of composite body
odour samples using paired ttests (e.g., for the two-odour composites, the ratings of 19
composites were compared with 19 average scores from their constituent individual odour
pairs). To investigate sex differences in ratings of composite body odour samples, we used a
two-way analysis of variance (ANOVA) with odour type and sex as a factor (two levels: two-
and four-composite body odours and two levels: male, female, respectively). To explore
whether composite body odour samples retain qualities of the individual odours, we first
ranked the individual samples of either sex based on their attractiveness ratings and then
split two- and four-composite body odours by the median value of the constituent samples.
Subsequently, we compared the above median and below median samples by an independent
samples ttest. In what follows, mean values calculated from ratings of the individual samples
and actual ratings of the composite body odour samples are referred to as calculated samples
and rated samples, respectively. We also tested for possible relationships between individual
samples and composite body odour samples using bivariate correlations.
Results
Ratings of the Individual Versus Composite Body Odours
We found no significant differences between mean ratings of the individual samples and
composite body odour samples (Figure 1; all ps>.16; for detailed results, see Tables 1
and 2). These means were calculated from the full sample of raters (i.e., both male and
female raters). Subsequently, we performed a two-way ANOVA for ratings of only
opposite-sex odour samples. This also did not reveal any significant differences in women’s
ratings of individual, two- and four-composite male odour samples, neither for pleasantness,
F(2, 68) ¼0.008, p¼.992; attractiveness, F(2, 68) ¼0.159, p¼.854 or intensity,
F(2, 68) ¼0.287, p¼.752. Similarly, there were no significant differences in men’s ratings of
individual, two- and four-composite female odour samples, for pleasantness, F(2, 30) ¼0.605,
p¼.553; attractiveness, F(2, 30) ¼0.726, p¼.492 or intensity, F(2, 30) ¼0.017, p¼.983.
To test whether composite body odours retain properties of the individual samples, we
split two- and four-composite body odours by the median value of the constituent samples.
We found that two-composite body odours consisting of above median samples were
perceived as more pleasant, t(16) ¼6.213, p<.001; attractive, t(16) ¼6.466, p<.001 and
intense, t(16) ¼7.756, p<.001, compared with below median samples. However,
differences were not significant in four-composite body odours either in pleasantness,
t(6) ¼0.437, p¼.678; attractiveness, t(6) ¼0.601, p¼.570 or intensity, t(6) ¼0.387,
p¼.712; see Figure 2(a) and (b). For explorative purposes, we further performed
Fialova
´et al. 5
a one-way ANOVA comparing individual four-composite samples and found significant
differences in their attractiveness, F(8, 349) ¼9.744, p<.001. A Tukey post hoc test
revealed that Sample 1 was rated significantly more attractive than Sample 5 (p¼.042)
and Samples 8 and 9 (p<.001). Moreover, Sample 2 was significantly more attractive than
all samples (p¼.05) except Sample 1 (see Figure 3).
Sex Differences in Ratings of the Composite Body Odours
A two-way ANOVA showed that male and female ratings did not significantly differ in
pleasantness, F(1, 52) ¼1.092, p¼.301; attractiveness, F(1, 52) ¼1.143, p¼.290 and
Figure 1. Mean ratings (95% CI) of calculated individual (white bars), rated two- (light grey bars) and
four- (dark grey bars) composite body odour samples concerning their pleasantness, attractiveness and
intensity. The individual samples were assessed by 110 raters and composite stimuli by 98 raters using 7-point
scale (e.g., 1 ¼very unpleasant and 7 ¼very pleasant).
6i-Perception 9(3)
intensity, F(1, 52) ¼0.575, p¼.452, nor was there any interaction between rater sex and
number of composite body odour samples, for pleasantness, F(1, 52) ¼0.040, p¼.842;
attractiveness, F(1, 52) ¼0.108, p¼.743 or intensity, F(1, 52) ¼0.060, p¼.807.
Correlation Between Individual and Composite Body Odours
We found significant positive correlations between ratings of two- and four-composite body
odour samples and mean values of the individual odours, for pleasantness (two-samples:
r¼.663, p¼.002; four-samples: r¼.783, p¼.013), attractiveness (two-samples: r¼.647,
p¼.003; four-samples: r¼.873, p¼.002) and intensity (two-samples: r¼.603, p¼.006;
four-samples: r¼.589, p¼.095; see Figure 4(a) and (b), Tables 3 and 4).
Correlation Between Ratings of Characteristics
Very strong positive correlations between pleasantness and attractiveness ratings (two-
samples: r¼.998, p<.001; four-samples: r¼.981, p<.001), and very strong negative
correlations between pleasantness and intensity (two-samples: r¼.862, p<.001; four-
Table 2. Comparison of Mean Ratings (SD) of the Individual Samples and Two- and Four-Composite Body
Odour Samples Concerning Their Pleasantness, Attractiveness and Intensity.
Characteristic Individual sample/composite M(SD) Paired samples tdfpCohen’s d
Pleasantness 1 3.16 (0.81) 1 2 0.25 18 .8 0.09
2 3.08 (1) 1 4 0.48 8 .64 0.05
4 3.2 (0.73) 2 4 1.02 8 .34 0.14
Attractiveness 1 3.1 (0.75) 1 2 0.98 18 .34 0.26
2 2.87 (0.98) 1 4 0.08 8 .94 0.07
4 3.05 (0.69) 2 4 0.87 8 .41 0.21
Intensity 1 4.06 (1.06) 1 2 0.35 18 .73 0.09
2 4.16 (1.08) 1 4 0.17 8 .87 0.1
4 3.97 (0.76) 2 4 0.62 8 .55 0.2
Table 1. Differences Between Mean Ratings (SD) of Pleasantness, Attractiveness and Intensity of the
Actually Rated Composite Body Odour Samples and Mean Values Calculated From Ratings of the Respective
Individual Samples.
Composite Characteristic M(SD)tdfpCohen’s d
2 Pleasantness Rated 3.08 (1.0) 0.56 18 .58 0.1
Calculated 3.17 (0.73)
2 Attractiveness Rated 2.87 (0.98) 1.48 18 .16 0.37
Calculated 3.13 (0.16)
2 Intensity Rated 4.16 (1.08) 0.63 18 .53 0.17
Calculated 4.03 (0.19)
4 Pleasantness Rated 3.2 (0.73) 1.11 8 .3 0.25
Calculated 3.38 (0.72)
4 Attractiveness Rated 3.05 (0.69) 2.11 8 .67 0.35
Calculated 3.29 (0.68)
4 Intensity Rated 3.97 (0.76) 0.59 8 .57 0.18
Calculated 3.81 (0.96)
Fialova
´et al. 7
Figure 3. Mean attractiveness ratings (95% CI) of four-composite body odour samples. Numbers at
individual bars indicate rank of each sample based on mean values calculated from attractiveness ratings of the
respective individual odours.
Figure 2. Mean attractiveness ratings (95% CI) of (a) two-composite body odours and (b) four-
composite body odours above (white bars) and below (grey bars) the median. Asterisk indicates level of
significance; ***p<.001 level.
8i-Perception 9(3)
samples: r¼.936, p<.001) and between attractiveness and intensity (two-samples:
r¼.856, p<.001; four-samples: r¼.913, p¼.001) were found (for more details, see
Tables 3 and 4).
Discussion
The main aim of this study was to test whether composite body odours are rated more
positively as compared with the individual samples collected from the same individuals.
Figure 4. Positive correlation between attractiveness ratings of (a) two-composite body odour samples
(r¼.63) and (b) four-composite body odour samples (r¼.87) and mean values calculated from ratings of the
respective individual odours. Dashed lines indicate 95% CI.
Fialova
´et al. 9
The rationale was that composite body odours might be more positively perceived because
they would be more ‘‘average,’’ as analogously observed in facial attractiveness studies, and
perhaps because they perceptually mimic the odour of relatively heterozygous individuals.
Contrary to expectation, we did not find significant differences between ratings of the
individual samples and both two- or four-composite body odours, and the same pattern
was observed for ratings of opposite-sex samples. Similarly, we did not find any positive
association between the number of individual body odours constituting composite odours
and its attractiveness ratings, as has been observed in facial images. However, we did find
significant positive correlations between ratings of two- and four-composite body odours and
calculated values of individual odours.
Moreover, our results suggest that two-composite body odour samples retain qualities of
the constituent individual odours as we found significant differences between the lower and
upper halves of the distribution. The differences were not significant for four-composite body
odour samples, perhaps as a consequence of limited sample size, but visual inspection of the
data (see Figure 3) indicates that four-composite body odour samples do appear to retain the
qualities of the individual constituent samples.
As described earlier, our research was inspired by studies on facial attractiveness. These
studies systematically show that composite facial images are perceived as more attractive than
the constituent images (Langlois & Roggman, 1990). This was also observed to be
independent of their higher bilateral symmetry (Rhodes et al., 1999), another factor
Table 4. Correlation Between Ratings of Four-Composite Body Odour Samples (Rated—R) and Individual
Odours (Calculated—C).
Pleasantness
R
Attractiveness
R
Intensity
R
Pleasantness
C
Attractiveness
C
Intensity
C
Pleasantness R .981*** .936*** .783* .805** .638
Attractiveness R .913** .864** .873** .741*
Intensity R .672* .703* .589
Pleasantness C .992*** .914**
Attractiveness C .928***
Intensity C
Note. Asterisks indicate level of significance; *p<.05. **p<.01. ***p<.001.
Table 3. Correlation Between Ratings of Two-Composite Body Odour Samples (Rated—R) and Individual
Odours (Calculated—C).
Pleasantness
R
Attractiveness
R
Intensity
R
Pleasantness
C
Attractiveness
C
Intensity
C
Pleasantness R .998*** .862*** .663** .652** .515*
Attractiveness R .856*** .647** .636** .486*
Intensity R .659** .631** .603**
Pleasantness C .988*** .881***
Attractiveness C .866***
Intensity C
Note. Asterisks indicate level of significance; *p<.05. **p<.01. ***p<.001.
10 i-Perception 9(3)
contributing to perceived attractiveness (Little & Jones, 2003). The attractiveness of
composite images thus appears to be due to their higher prototypicality (Rhodes &
Tremewan, 1996); that is, they represent an average facial morphology and may thus
mimic heterozygosity in individual faces. These processes are, however, far from how the
olfactory system perceives chemical mixtures. Several previous studies have shown that odour
mixtures might be perceived quite differently from their constituents (e.g., Thomas-Danguin
et al., 2014). Some scholars thus refer to odour mixtures as having emergent perceptual
qualities that are frequently difficult to predict from the qualities of the constituents.
Furthermore, it has been shown that humans, including professional ‘‘noses,’’ perform
rather poorly in identifying individual chemicals from odour mixtures (Jinks & Laing, 1999).
Another possible mechanism is that higher attractiveness of facial composites, due to their
prototypicality, is frequently perceived as more familiar. Unfortunately, we did not collect
these ratings. Thus, whether composite body odours are perceived as more familiar remains
an open question.
Limitations
In our study, we employed as body odour donors and raters women using hormonal
contraception to avoid possible fluctuations in body odour attractiveness (Havlı
´c
ˇek,
Dvor
ˇa
´kova
´, Bartos
ˇ, & Flegr, 2006; Kuukasjarvi et al., 2004) and olfactory abilities
(Martinec Nova
´kova
´et al., 2014) during regular menstrual cycling. A previous study has
revealed shifts in MHC-related body odour in contraceptives users (Roberts, Gosling, Carter,
& Petrie, 2008), and one may thus argue that our null findings might be thus attributable to
the fact that we employed contraceptive users. However, a recent meta-analysis did not show
significant differences related to preferences for MHC dissimilarity between contraceptive
users and nonusers (Winternitz et al., 2017). In any case, the main advantage in employing
hormonal contraceptive users as body odour donors was that we aimed to limit the known
effect of cyclic fluctuations, which could drastically interfere with the process of creating
blends across individual donors of different cycle phases. We suggest that this step should
only increase, and not interfere with, the chance to observe a positive effect of composite
body odours because it reduces noise in the collected samples. It is also worth noting that
studies of facial composite images, which find robust effects, did not similarly control for
effects of hormonal contraception in women either contributing facial photographs or ratings
(Langlois & Roggman, 1990; Rhodes & Tremewan, 1996; Rhodes et al., 1999); this seems to
us to suggest a likely sensory specificity in how composites of odours and faces are perceived.
Another potential limitation is that, when assessing individual odours and two-composite
body odour samples, raters were presented with either one complete cotton pad or two
halves, but four-composite samples were created using four halved pads. The difference in
the amount of presented material may potentially affect perception of body odour intensity.
However, this does not seem to be the case, as we did not find any significant differences
between pleasantness, attractiveness and intensity ratings of the individual samples and two-
and four-odour composites.
Implications for Future Studies
Several previous studies have employed composite body odours from individuals sharing
characteristics of interest, for example, their sexual orientation (Martins et al., 2005) or
affective state (Pause et al., 2004), with the unstated assumption that shared features of the
individual odours would be perceivable in the composite stimuli. Our results indicate that
Fialova
´et al. 11
individual hedonic qualities, at least, are retained in the odour composites, although further
study is needed to investigate the retention of other trait-specific cues. We created
composites from individual odours similar in their attractiveness, as this was the most
efficient way to test the effect in question. However, it remains an open question as to
whether composites made of individual odours that are more variable in hedonic quality
would be perceived simply as an average of the constituents or whether such mixtures
would show some different, emergent quality. Previous studies investigating interactions
between individual body odour and perfume have shown that qualities of the resulting
blends cannot be reliably predicted (Sobotkova
´et al., 2017). In a related study, one of the
components was kept constant (i.e., the odour donors applied the same perfume),
nevertheless the variability in hedonic quality of the blends was comparable with that
seen in the body odours alone (Lenochova
´et al., 2012). Whether patterns observed in
studies on perfume-body odour blends can be generalized to the blends of individual
body odours should be addressed in future studies.
Remarkably, it has been repeatedly shown that even though perceived qualities of body
odour samples tend not to differ during hedonic assessment (e.g., pleasantness), they do
induce other effects on individuals exposed to these stimuli, for example, in their
autonomic response (Adolph, Schlo
¨sser, Hawighorst, & Pause, 2010), anxiety levels
(Albrecht et al., 2011) or cognitive functioning (Chen, Katdare, & Lucas, 2006; Gelstein
et al., 2011). This evidence suggests that lack of consciously perceived differences does not
exclude the possibility of odours transferring other socially relevant cues.
Finally, our findings cannot be interpreted as evidence against a link between
heterozygosity and attractiveness. Previous studies indicate that individual body odour
samples provide cues to heterozygosity (Thornhill et al., 2003), and this might be
specifically linked to heterozygosity in MHC genes that is important in MHC-based mate
choice providing direct fitness benefits (Havlı
´c
ˇek & Roberts, 2009; Winternitz et al., 2017).
Nevertheless, our results demonstrate that the validity of composite body odour samples to
test hypotheses about heterozygosity might be limited. It also provides a caution for scholars
primarily interested in testing evolutionary hypotheses that the proximate mechanisms that
underlie interpreted functional outcomes must be treated with extreme care.
Acknowledgements
The authors would like to thank all the volunteers and Vı
´tTr
ˇebicky´ for many helpful advices and help
with statistical analysis and two anonymous reviewers for their valuable comments.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or
publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or
publication of this article: This work was supported by a Czech Science Foundation grant (J. F. and J.
H., GAC
ˇR 18-15168S), by the project ‘‘Sustainability for the National Institute of Mental Health,’’
under grant number LO1611, with a financial support from the Ministry of Education, Youth and
Sports of the Czech Republic under the NPU I program, and statutory research funds (A. S.).
12 i-Perception 9(3)
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How to cite this article
Fialova
´, J., Sorokowska, A., Craig Roberts, S., Kubicova
´, L., & Havlı
´c
ˇek, J. (2018). Human body
odour composites are not perceived more positively than the individual samples. i-Perception,
9(3), 1–15. doi:10.1177/2041669518766367
Fialova
´et al. 15
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Introduction: Cycle-correlated variation in olfactory threshold, with women becoming more sensitive to odors mid-cycle, is somewhat supported by the literature but the evidence is not entirely consistent, with several studies finding no, or mixed, effects. It has been argued that cyclic shifts in olfactory threshold might be limited to odors relevant to the mating context. Aims: We aimed to test whether the evidence currently available points in the direction of odor-specific or, rather, general changes in olfactory sensitivity and, if the former is the case, to what group of odorants in particular. Materials and Methods: We carried out a meta-analysis of relevant studies which together used a variety of different odorants, including some found in food, body odor and some that occur in neither of these. First we tested whether there appears to be an overall effect when all studies are included. Next, we hypothesised that if cyclic changes in olfactory processing are odor-specific and tuned to biologically relevant odors, we should find changes in detection thresholds only for odorants found in body odor, or for those that are perceptually similar to it. In contrast, if threshold patterns are linked to more general fluctuations in odor processing across the cycle, we would not expect changes in relation to any particular odorant group. Results: The results support the view that there is significant cycle-correlated variation. Thresholds were in general significantly lower in the fertile than the non-fertile phases, with effect sizes consistently in this direction. This same conclusion applied to both ‘food’ and ‘musky’ odorants, despite their different evolutionary significance, and to the androgen steroids (androstadienone, androstenone, and androsterone), but could not be applied to phenyl-ethyl alcohol. Discussion: The results indicate that olfactory sensitivity may be a non-adaptive by-product of the general physiological fluctuations or differences in neural processing experienced across the cycle to a broad spectrum of odorants, rather than being specifically selected for mate choice-related odors.
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