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- Abstract
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- The contagious aspect of yawning is a
well-known phenomenon that exhibits variation in
the human population. Despite the observed
variation, few studies have addressed its
intra-individual reliability or the factors
modulating differences in the susceptibility of
healthy volunteers. Due to its obvious
biological basis and impairment in diseases like
autism and schizophrenia, a better understanding
of this trait could lead to novel insights into
these conditions and the general biological
functioning of humans. We administered 328
participants a 3-minute yawning video stimulus,
a cognitive battery, and a comprehensive
questionnaire that included measures of empathy,
emotional contagion, circadian energy rhythms,
and sleepiness. Individual contagious yawning
measurements were found to be highly stable
across testing sessions, both in a lab setting
and if administered remotely online, confirming
that certain healthy individuals are less
susceptible to contagious yawns than are others.
Additionally, most individuals who failed to
contagiously yawn in our study were not simply
suppressing their reaction, as they reported not
even feeling like yawning in response to the
stimulus. In contrast to previous studies
indicating that empathy, time of day, or
intelligence may influence contagious yawning
susceptibility, we found no influence of these
variables once accounting for the age of the
participant. Participants were less likely to
show contagious yawning as their age increased,
even when restricting to ages of less than 40
years. However, age was only able to explain 8%
of the variability in the contagious yawn
response. The vast majority of the variability
in this extremely stable trait remained
unexplained, suggesting that studies of its
inheritance are warranted.
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- Spontaneous yawning, which occurs more
frequently when one is bored or tired, is a
deeply rooted, phylogenetic trait that is
widespread among vertebrates [1]. In
contrast, contagious yawning, which can be
triggered in response to hearing, seeing,
reading, or thinking about yawning
[2]-[4], has only been
definitively demonstrated in humans and
chimpanzees[3], [5]. The ability
to yawn spontaneously begins in humans in utero
by 20 weeks of gestation, but contagious yawning
does not reliably develop in humans or chimps
until childhood [6]-[9].
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- While much speculative theory has gone into
understanding the primary function of yawning,
no scholarly consensus has been reached or
substantiated. Theories range markedly from a
thermoregulatory function, i.e., cooling of the
brain and increased oxygen consumption, to
behavioral synchronization and
communication[10], [11]. The
contagious aspect of yawning remains a
well-known yet poorly understood phenomenon
despite the ability to induce yawning in a
laboratory setting from finite stimuli, efforts
to identify the underlying neural mechanism, and
reported associations with empathy.
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- Evidence for the role of empathy in
contagious yawning spans disciplines and has
lent support to the empathetic modeling
hypothesis[12]. Studies have found
susceptibility to contagious yawning to be
correlated with empathic aspects like faux pas
theory of mind tasks, self-face recognition, and
scores on standardized empathy scales
[2], [12], [13].
Intriguingly, patients with either autism
spectrum disorder or schizophrenia, both of
which exhibit impaired social resonance,
demonstrate reduced contagious yawning despite
spontaneous yawning remaining intact
[13]-[15]. Further support for
the role of empathy stems from a longitudinal
behavioral study demonstrating a positively
modulated contagious yawning frequency and
latency along the following cline of increasing
social bond:
stranger?acquaintance?friend?kin[16]. An
experiment in chimpanzees, who display at least
basic levels of empathy, furthered this finding
by demonstrating increased contagious yawning in
response to in-group, compared to out-group,
yawners[17]-[19].
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- Neuroimaging studies have also provided
support for the role of empathy in this trait.
Despite divergent reports on the recruitment of
the human motor neuron system (MNS), there is
general consensus that contagious yawning
recruits the neural network involved in
cognitive empathy[2],
[20]-[22]. The MNS may allow for
shared emotional and physiological states based
on motor patterns [23] and has been
previously demonstrated to be more active in
empathic individuals[24]. By evaluating
unique patterns of activation during contagious
yawning, it has also been demonstrated that
structures implicated in self-processing and
mentalizing, such as cortical midline
structures, are recruited during the contagious
yawning response[20].
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- In controlled studies, approximately 40-60%
of healthy volunteers yawn in response to a yawn
stimulus [3], [4], [12].
Despite this variability, relatively little is
known about factors that may influence
individual susceptibility to contagious yawning
beyond empathy. Purported associations have
additionally been made with subjective measures
of intelligence, time of day, and climate
conditions [7], [25],
[26]. However, studies with larger
sample sizes have generally not assessed
multiple factors simultaneously and have been
limited in scope. Additionally, the effect of
being observed is inhibitory to contagious
yawning[27], [28], which has
made studying this trait in a more naturalistic
setting a possibly ideal, yet underexplored
approach. In particular, no studies have yet
assessed whether susceptibility to contagious
yawning remains stable when participants are
tested both in a laboratory setting and in an
uncontrolled setting outside of the laboratory.
Only one study has ever assessed whether an
individual's susceptibility is stable from one
laboratory-based testing session to the
next[3].
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- Here, we aim to better define the role of
various factors in susceptibility to contagious
yawning by systematically assessing the effect
of basic demographics, testing conditions,
empathy, cognitive performance, time of day, and
other variables on the response of healthy
controls to a brief contagious yawning video
stimulus. We also aim to define the stability of
susceptibility to contagious yawning using our
developed yawning stimulus in a laboratory and
natural setting. Our overall, long-term goal in
characterizing variability in this trait is to
create a novel viewpoint into the pathways
behind human diseases like schizophrenia and
autism, as well as general human functioning, by
identifying the genetic basis of normal
variation in this genetically understudied, yet
clearly biological, trait. The presented work
represents the most comprehensive
characterization of factors influencing
contagious yawning to date.
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Discussion
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- We assessed the impact of multiple factors
on contagious yawning susceptibility in a group
of 328 healthy volunteers who exhibited
contagious yawning frequencies that were similar
to those from the previous literature
[3], [4]. Our results reveal
that variables like empathy, tiredness, and
Circadian preference have little effect on
contagious yawning susceptibility and that the
contagious yawning response of individuals is
stable over a two-month period, whether they are
tested in the lab, or off-site via an online
test.
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- The results demonstrate that the age of the
participant was the only variable with a
significant influence on whether or not they
yawned. This association was not simply the
result of the wide range of ages assessed here
(Figure 5); even when restricting to
participants aged below 40, age was still the
only significant predictor of susceptibility to
contagious yawning. Despite this strong
association, age was only able to explain 8% of
the variation in the yawning response, leaving
the majority of variation unexplained by any
known factors. Interestingly, a reduction in
yawning frequency has been previously
demonstrated in aged individuals, though never
previously in a contagious context
[42].
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- Our results are in contrast to previous
studies, which have identified correlations
between yawning susceptibility and empathic
abilities, time of day, and subjective measures
of intelligence [7], [12],
[13], [25]. The IRI Fantasy,
which gauges one's capacity for cognitive
empathy and was previously demonstrated to
influence susceptibility to contagious yawning
in a sample of 45 healthy controls [13],
was not a significant predictor of
susceptibility in our study when taking age into
account, despite the general viewpoint that
contagious yawning must be a product of empathy
[12], [14], [43],
[44]. Our participants were measured for
several aspects of empathy, including all four
portions of the well-known IRI and an
established emotional contagion test. While the
sample size for the empathy scales was smaller
than the sample size for the rest of our study,
the number of participants measured was still
larger than the majority of previous studies on
contagious yawning and would have been more than
sufficient to pick up a strong effect. This lack
of association suggests that contagious yawning
is not simply a product of one's capacity for
empathy.
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- When examining variables individually in
univariate logistic regression analyses, we did
identify associations between contagious yawning
susceptibility and education, whether one was
currently a student, cognitive performance,
Circadian preference (CIRENS), empathy (IRI
Fantasy subscale), and current tiredness.
However, these variables were all even more
strongly associated with the age of the
participant and were no longer significantly
associated with contagious yawning
susceptibility when taking age into account.
While the associations between these factors and
age were largely already known to exist
[45]-[48], the reason for the
association between contagious yawning and age
remains unknown, offering a direction for future
exploration. Possible explanations for this
strong, inverse association could include
decreased attention to the stimulus with age, a
reduced connection to the yawners in the video
due to use of technology, or a general decline
in susceptibility to contagious yawning as we
age.
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- To our knowledge, only one previous study of
37 participants has measured the test-retest
reliability of a contagious yawning
susceptibility test [3]. Our work
demonstrates high reliability in individual yawn
responses to a 3-minute yawn stimulus video,
whether it is taken twice outside the lab or
once in the lab and then a second time outside
the lab. While the correlation between the two
test sessions was lower in the in-lab/off-site
repeat session, this is not unexpected given the
change in testing conditions. Furthermore, both
sets of correlations for these repeat sessions
are comparable to those of the previous work,
despite the difference in our testing locations
and even though our studies differed markedly in
length, stimulus type and sample size. Our
results provide new evidence for the stability
of contagious yawning susceptibility across
testing sessions and locations and indicate that
constant differences exist between healthy
controls in their susceptibility.
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- This study does have some limitations. It is
worth noting that our goal was not to describe
the frequency of yawns in response to a specific
video, but rather to reliably measure
differences between individuals in their
response to a short, standardized yawn stimulus.
We therefore make no claims about the precise
frequency of contagious yawns elicited by the
video stimulus. In addition, participants were
primed with a brief description of contagious
yawning, which may have contributed to the
slightly elevated percentage of contagious
yawners in our population; it is also possible
that some recorded yawns were actually
spontaneous yawns. We did not directly observe
the participants, in contrast to many previous
contagious yawning studies. This method was
chosen because the high word of mouth
advertisement about our study makes secretive
procedures like surreptitious observation
difficult to maintain for all participants. The
strong test-retest correlation demonstrates that
our method is valid and is in accordance with a
previous study showing that participants were
able to accurately record their own yawns while
being secretly videotaped [39].
Additionally, we employed several self-report
scales that may not accurately reflect, for
example, the true empathy or circadian
preference of the participant. Nonetheless,
these scales are either current standards in the
field or are well correlated with them,
providing us with the best representation of
these traits that is available with a brief
questionnaire. Finally, we interpreted pseudo r2
values from the logistic regression models as
approximations of the amount of variation in
contagious yawning explained by the variables
investigated, although these values cannot be
interpreted as reliably as can the traditional
r2 values from linear regression models.
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- Despite these limitations, our work clearly
demonstrates the stability of intra-individual
variation in susceptibility to contagious
yawning, a significant negative correlation
between age and the contagious yawning response,
and the inability of any known variables to
explain the vast majority of variation in
contagious yawn responses. This extensive,
unexplained, and highly replicable variation
between individuals in their susceptibility
suggests the existence of an underlying genetic
influence and warrants future studies assessing
the inheritance of this unique trait.
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