Many diverse species yawn, suggesting
ancient evolutionary roots. While yawning is
widespread, the observation of contagious
yawning is most often limited to apes and other
mammals with sophisticated social cognition.
This has led to speculation on the adaptive
value of contagious yawning. Among this
speculation are empirical and methodological
assumptions demanding re-examination. In this
paper we demonstrate that if yawns are not
contagious, they may still appear to be so by
way of a perceptual pattern-recognition error.
Under a variety of conditions (including the
assumption that yawns are contagious) we
quantify (via models) the extent to which the
empirical literature commits Type-1 error (i.e.,
incorrectly calling a spontaneous yawn
'contagious'). We report the results of a
pre-registered behavioural experiment to
validate our model and support our criticisms.
Finally, we quantify - based on a synthesis of
behavioural and simulated data - how
'contagious' a yawn is by describing the size of
the influence a 'trigger' yawn has on the
likelihood of a consequent yawn. We conclude by
raising a number of empirical and methodological
concerns that aid in resolving higher-order
questions regarding the nature of contagious
yawning, and make public our model to help aid
further study and understanding.
Introduction
When Provine (1986) initiated modern
academic interest in contagious yawning his
interest was in whether the yawn was a human
releasing stimulus, a stimulus which, when
observed by another, 'releases' or elicits
unlearned behaviour (Thorpe 1963; Yoon and
Tennie 2010; Zentall 2001). The yawn seemed a
likely candidate at a time when few examples had
been previously identified in humans
(Eibl-Eibesfeldt 1975). Provine established the
standard protocol for the observation of yawns:
show participants videos (or audio, or written
descriptions) of yawns for several minutes and
count the number of yawns observed. Then compare
this number to the number of yawns observed when
participants are exposed to other, equally
identifiable stereotypic motor patterns (such as
hiccups, sneezes, or laughter). On the face of
it, the observation that yawns are contagious
was reasonable, with written descriptions dating
back at least as far as 300 BCE (Zimara 1580).
Provine's interest was what yawning, as a
releasing stimulus, revealed about our neurology
and our evolutionary history, an interest that
has continued to this day (for reviews see:
Gallup 2011; Guggisberg et al. 2010, Guggisberg
et al. 2011).
In the ethological literature (distinct from
the medical literature), a contagion is a
short-term spread of a species-specific
behaviour aroused by a specific stimulus (often
behaviour) expressed in others in a coordinated
manner (Armstrong 1951; Thorpe 1963; Yoon and
Tennie 2010; Zentall 2001). Examples may include
mating displays, formidability displays, and
flocking behavior. A contagious response is a
very low-level cognitive response contingent
primarily upon one's perception of the stimuli.
And yet, perception is a necessary but not
sufficient explanation: it is known that yawn
contagion is primarily a function of social
considerations. We are far more likely to yawn
to close family and friends, than we are to
strangers or acquaintances (Demuru and Palagi
2012; Norscia and Palagi 2011); indeed, empathy,
theory of mind, self-awareness, and
psychopathy-related traits are all associated
with one's tendency to yawn contagiously
(Bartholomew and Cirulli 2014; Norscia et al.
2016; Palagi et al. 2009; Platek et al. 2003;
Rundle et al. 2015). Contagious yawning has been
observed in non-humans, and is typically
associated with that species' social abilities
(Demuru and Palagi 2012; Gallup et al. 2015;
Madsen et al. 2013; Palagi et al. 2009; Romero
et al. 2014). While there are other explanations
that are possible alternatives to 'contagion'
(Yoon and Tennie 2010), we will not further
discuss these alternatives, as we intend to
explore the status quo explanation:
contagion.
So how seriously should we take the
observation that yawns are contagious?
Certainly, in groups, humans yawn. Not only do
we see a temporal and spatial relation between
yawning individuals, but we have an easily
identified subjective experience associated with
our own personal need to yawn in response to
others. And yet in an abstract sense, much like
the incorrect observations associated with the
hot-hand fallacy (that basket-ball shooters have
streaky performance which predicts future
behaviour; Burns and Corpus 2004; Gilovich et
al. 1985), the observation that yawning is
contagious may have arisen as a consequence of
our tendency to see patterns and causation where
none exists, to misinterpret the clumpiness of
randomness as something else. That is, the
observation of contagion in groups is a
perceptual misunderstanding of randomness, and
is a phantom-signal in the noise. While at a
personal level, confirmation bias, in which
situations that conform to our expectations are
salient and memorable while those that fail to
are not, could easily (and erroneously) lend
weight to the claim that yawns are contagious.
Human yawning is associated with the time of day
(Zilli et al. 2007), fatigue or boredom
(Baenninger and Greco 1991; Provine and Hamernik
1986), various medical or psychological
afflictions (Daquin et al. 2001; Walusinkski
2009), the temperature of one's brain (Gallup
2011; Gallup and Gallup 2008; Shoup-Knox et al.
2010) and, in experimental contexts, whether or
not one is being observed (Baenninger and Greco
1991; Gallup et al. 2016). Indeed, when one's
intent is to observe yawn contagion it is
famously difficult; Baenninger and Greco (1991)
wrote "in our laboratory we have consistently
failed to find contagion of yawning when
subjects are being openly observed" (pp. 454;
that yawns are difficult to observe openly under
laboratory conditions - for any researcher -
should give pause for concern: for it is the
opposite of our everyday experiences and
observations - contagious yawns are almost
always made or seen when being 'openly observed'
in communal places).
Human children yawn, but do not appear to do
so contagiously until about the age of 5 or 6
(Anderson and Meno 2010; likewise in
chimpanzees, Madsen et al. 2013), and as age
increases in adulthood, the likelihood of
catching a yawn decreases (Bartholomew and
Cirulli 2014). Considering all the apparent
boundary conditions associated with the
production of both spontaneous and contagious
yawning, it may be that the null hypothesis has
not been considered seriously enough. Yawns are
primarily only measured in the lab, under
constrained circumstances after exposing
participants to minutes of stimuli. Their
co-occurrence in naturalistic settings is
contingent upon a range of factors, all of which
can produce an apparent sensation of contagion,
despite the fact that logic (and statistics)
suggest that even if yawns weren't contagious,
they may appear as if they were.
Independent of this, there is also a problem
with analysis which could lead to an
over-estimation of how likely yawns are to
occur, and what the typical latency of contagion
is. Amidst an increasingly vocal cry for more
rigour in statistical and experimental processes
in the social sciences (Gelman and Loken 2013;
Simonsohn et al. 2014a; Simonsohn et al. 2014b),
there are indications that measures don't
adequately handle Type-I error, or rule-of-thumb
type heuristics are applied to intuitively
handle the error. For example, as recently as
last year, Gallup et al. (2016) wrote: "Since
the rate of spontaneous yawning is quite
infrequent, and studies have demonstrated that
participants yawn much more frequently when
watching a video stimulus depicting yawns
compared to control stimuli, we can be confident
that the vast majority of yawns reported in the
current experiment were contagious [rather
than spontaneous]" (pp. 3), and Norscia et
al. (2016) that: "…we recorded yawn
responses within a 3 min (sic) time window, thus
reducing the probability of mistakenly coding
spontaneous yawns as yawn responses" (pp. 3;
emphasis added). Miscategorization of noise as
signal, even within a conservative window,
falsely inflates reported rates of focal
behaviour. Even in studies where yawns are
observed in control conditions, no attempt is
made to use this information to inform the
accuracy of the observations in test conditions.
It is not enough to simply say that the
treatment condition produced more yawns than the
control, since the control produced yawns at a
rate above 0. How many yawns in the treatment
condition, then, were the product of the
stimuli, and how many would have been produced
independent of the stimuli?.1 The rate of Type-1
error should be a serious concern, particularly
since methods vary widely. Some studies
categorize as contagious any yawn that occurs up
to 5-min after a trigger yawn (Madsen et al.
2013; Palagi et al. 2009; Provine 1986), some
limit this to 3-min (Demuru and Palagi 2012;
Norscia et al. 2016; Norscia and Palagi 2011)
and some do not report at all the window in
which they consider a yawn spontaneous or
contagious (Bartholomew and Cirulli 2014; Platek
et al. 2003). Moreover, some authors exclude
yawns that occur in the appropriate window of
time if they cannot directly attribute it to a
single trigger (thus systematically biasing
latency measurements and ignoring base-rates;
Demuru and Palagi 2012; Norscia et al. 2016;
Norscia and Palagi 2011). Independent of this,
the difficulty of observing contagious yawns in
the wild has led researchers to employ extreme
induction methods in the lab. Many studies
expose participants to literally minutes of
continuous yawning on various media (Bartholomew
and Cirulli 2014; Gallup et al. 2016; Madsen et
al. 2013; Massen et al. 2015; O'Hara and Reeve
2011; Provine 1986, 1989). Taken together, the
measurement and analyses of contagious yawns is
far removed from the conditions under which most
people believe contagious yawns occur - i.e.,
when being openly observed among others, after
only a brief exposure, and with only a brief
latency (see: Results).
One possible solution in the management of
these kinds of errors is the use of Agent-Based
Modelling (ABM). Agent-Based Models simulate
interacting agents according to given rules of
conduct. In so doing complicated emergent
phenomena can be observed and measured. The
'Game of Life', and cellular automata more
generally, are excellent and historic examples
of this approach (Gardner 1970). An additional
benefit of using models to understand social
phenomena is that the building of such models
requires the model's author to make explicit
assumptions that may be hidden using natural
language (Marewski and Olsson 2009). For
example, spontaneous yawns are produced
according to a number of factors, but how
frequently do they occur? If I were to observe
two 'trigger' yawns in quick succession, am I
more likely to yawn contagiously than if I only
observed one? What about 3, or 12, or 99? Does a
trigger yawn leave a 'trace' such that I am more
likely to contagiously yawn again within a
certain time span, and if so, at what rate does
the trace degrade? Am I likely to respond to a
trigger at a diminishing linear rate, or is the
relationship curved? ABM's allow the easy
exploration of these questions, as well as
management of Type-1 error.
This paper describes one such model which
will address various questions: How contagious
are yawns? For how long is it appropriate to
consider a spontaneous yawn a 'trigger'? And how
often do we miscategorise a spontaneous yawn
(which necessarily must occur at a base
frequency) as a contagious yawn? We also
seriously examine the null hypothesis: if yawns
are not contagious, might it still look as if
they were? The model is first presented along
with data it produces based on hypothetical
input. Second, we present a behavioural study
closely matched to the model's design, in order
to ground the input and output variables.
Finally, the results are presented by matching
real data (from the behavioural experiment) to
the agent-based model in order to address (and
resolve) empirical and theoretical questions
associated with the topic of contagious yawning
(with both pre-registered and exploratory
analyses).
General Discussion
Do humans in groups yawn in each other's
presence more often than when alone? Certainly.
Our subjective and affective observations
suggest so, and both this data and a history of
(somewhat contrived) historic experiments have
demonstrated that the observation of yawns leads
to an increase in yawning. Is yawning contagious
(does the observation of a trigger yawn cause
one to yawn in response, in an unlearned
manner)? Maybe. An auto-correlation (which takes
input at one time and correlates it with input
with a time-lag) suggests that yawns are not
immediately contagious, and simultaneously
indicates we tend to yawn in clusters (indeed,
95% of all recorded yawns in the non-blind
condition occurred within 5-min of a yawn made
by the very same person). Perhaps more
critically though, it is demonstrated here that,
even if yawns were not contagious, it would be
an easy and predictable mistake to make to
conclude they were (an important observation,
one that has no precedent, and ought to stand as
evidence that the field has a blind-spot). If
yawns are contagious (and let's assume they are)
then it is also the case that we have a long and
documented history of willfully failing to
account for the miscategorization of contagious
yawns (by failing to assume that yawns are
produced at a base-rate). This has two
implications. First, we have over-estimated the
magnitude and meaning of a contagious yawn. Not
only do we often risk calling a spontaneous yawn
contagious when it is actually incidental, we
also omit from analyses a variety of data which
is too difficult to appropriately categorize.
This has led to the second problem; By using low
quality data in our theorizing on the
evolutionary significance of contagious yawns
(primarily in Homo), we may have been doing
little more than seeing faces in clouds or
reading tea-leaves.
To the extent that assumptions of the model
presented here seem insufficient or
unreasonable, we respond that we merely
formalized (in a programming language)
assumptions extant in the literature. We
acknowledge that yawns appear to vary throughout
the day and according to one's chronotype (Zilli
et al. 2007). Further, we acknowledge that
individual differences associated with social
awareness or mentalizing also bear upon one's
tendency to contagiously yawn (Bartholomew and
Cirulli 2014; Demuru and Palagi 2012; Norscia et
al. 2016; Norscia and Palagi 2011; Palagi et al.
2009; Platek et al. 2003; Rundle et al. 2015).
We acknowledge that some existing experimental
protocols are used to mitigate the influence of
social factors. And yet, we suggest that the
appropriate response to our provocative position
is not to appeal to our omission of these
factors and dismiss our claims, but rather, to
accept that this simple model can be improved to
better account for these important variables in
the future. This model and experiment should be
the starting point in re-examining and
attempting to falsify this phenomenon; it is not
intended to be a full-stop on the discussion and
conclusive statement that yawns aren't
contagious (or are with an exact factor of 2.65)
- merely that there are assumptions in the
literature that need reconsidering, and a formal
re-examining using alternative means (presented
herein) is one appropriate way to proceed.
In examining the ultimate role yawns play,
this paper has gone some way in answering
important questions. To what extent is Type-1
error a problem? It is non-trival. Is there a
causal relationship between a trigger and a
contagious yawn (more than can be inferred by
ANOVAs)? Maybe; if so, a single observed yawn
raises the likelihood of yawning by a factor of
about 2.65. Can this tool be applied to future
yawn research? Absolutely. How seriously have we
examined the null hypothesis? Not seriously
enough. Are there a variety of unasked questions
which are fundamental in allowing evolutionary
hypothesizing? YES!
In designing a formal model of yawn
contagion several important questions arose
which have not been sufficiently addressed in
the literature, and which have essentially been
buried by common methodologies: Is the
observation of one trigger yawn differentially
more or less influential than the observation of
two or more trigger yawns in the same period?
Given the current manner in which yawns are
aroused by way of minutes of continuous yawn
stimuli, this needs to addressed. To what extent
does contagion diminish over time, and what
shape does the trace decay over time? Present
assumptions about 3- and 5-min windows assume a
flat function that is equally contagious at each
minute after a trigger, but which returns to 0
after an arbitrary (and a-theoretical)
threshold. The present data and model (as well
as improved accountability in the future) might
better illustrate in what manner yawns are
contagious over time. Why is it so hard to
observe a contagious yawn in the wild? Because
they don't happen that often, and the increase
in likelihood above the base-rate is quite
modest (so modest that the observation of a true
effect in the wild is likely below our threshold
for being able to detect an effect of the given
magnitude). These, and other questions, need to
be answered to improve our understanding of what
it means to say 'yawns are contagious'.
In attempting to resolve and quantify some
of these questions, we can now ask more
important questions (that can hopefully resolve
current 'are for'-focused debates). To the
extent that yawns allow evolutionary inference,
we can now compare not just their role, but the
magnitude of their influence, to other
contagious behaviours. To the extent that yawns
are contagious and informative, are they more so
than, say, contagious itching (Feneran et al.
2013; Schut et al. 2015)? Contagious itching
shares many features with contagious yawning
(e.g., deep evolutionary history, associations
with environmental factors, personal history and
experience, social-cognitive factors, and
illness; Schut et al. 2015). Indeed it is
possible that itching is more contagious than
yawning, and the data presented herein goes
halfway to resolving that comparison. Likewise
for whether or not laughter (Provine 2004) or
smiles (Dimber et al. 2000; Surakka and Hietanen
1998), or any other social- and
socially-informed behaviour is more contagious
and informative than yawning. Inasmuch as it
makes sense to suggest that yawns are a
mechanism for facilitating social
synchronization (as one example), does it make
sense to say also that itching serves a similar
role? Only better resolution of these questions
(and more clearly quantified comparisons to
other contagious / releasing behaviours) can
inform our understanding.
There are several other approaches that can
address issues in this literature. As was the
case with this study, pre-registration can go
some distance to enhancing experimental
transparency, reducing experimenter degrees of
freedom, and forking-paths decisions, and will
not only influence what is measured and
reported, but what is published. Second, given
the historical precedent that yawning is
contagious (dating back to antiquity) it may be
reasonable to infer that the belief that yawns
are contagious (perhaps erroneously arrived at)
has spread to such an extent the belief itself -
that yawns are contagious (widely, but not
universally held) - accounts for considerable
variance in whether or not yawns are spread
within a group (thereafter maintained by pattern
recognition error and confirmation bias).
Measuring this as a variable, and potentially
undertaking significant cross-cultural research
to establish that evolutionary theorizing is
appropriate, is necessary for advancing the
field.
To conclude we make a singular claim: It is
time to take more seriously the null hypothesis
(and all this implies) and attempt to falsify
our claims. Our own subjective experience and
confidence that yawns are contagious needs to be
put aside so that our methods of induction and
attributions of contagious yawns can be
appraised for their appropriateness. Management
of type-1 error must be resolved. Other tools
for examining the phenomenon must now be
considered in determining how best to answer the
kinds of questions we're asking. To that end we
make our model publicly available with
instructions, and offer our services in
extending the model to account for wide range of
documented correlates and factors associated
with contagious yawning. We hope this will
underpin ongoing discussion and resolution of
longstanding debates.
