Abstract
Contagious yawning differs from spontaneous yawning because it occurs when an individual yawns in response to someone else’s yawn. In Homo sapiens and some non-human primates contagious yawning is higher between strongly than weakly bonded individuals. Up to date, it is still unclear whether this social asymmetry underlies emotional contagion (a basic form of empathy preferentially involving familiar individuals) as predicted by the Emotional Bias Hypothesis (EBH) or is linked to a top-down, selective visual attention bias (with selective attention being preferentially directed toward familiar faces) as predicted by the Attentional Bias Hypothesis (ABH). To verify whether the visual attentional bias explained the yawn contagion bias or not, in this study, we considered only yawns that could be heard but not seen by potential responders (auditory yawns). Around 294 of auditory yawning occurrences were extrapolated from over 2000 yawning bouts collected in free ranging humans for over nine years. Via GLMM, we tested the effect of intrinsic features (i.e., gender and age) and social bond (from strangers to family members) on yawn. The individual identity of the subjects (trigger and potential responder) was included as random factor. The social bond significantly predicted the occurrence of auditory yawn contagion, which was highest between friends and family members. A gender bias was also observed, with women responding most frequently to others’ yawns and men being responded to most frequently by others. These results confirm that social bond is per se one of the main drivers of the differences in yawn contagion rates between individuals in support of the EBH of yawn contagion.
Highlights
Yawning is an involuntary sequence of mouth opening, deep inspiration, brief apnea, and more or less slow expiration (Baenninger, 1997; Walusinski and Deputte, 2004; Guggisberg et al, 2010; Krestel et al, 2018)
The generalized linear mixed model (GLMM) indicated a significant effect of the sex of both triggers and responders, and of bonding: yawn contagion of female responders was higher compared to males (Figure 3), and males, as triggers, were responded to more frequently by
The highest levels of auditory yawn contagion in women compared to men confirm the gender bias observed in naturalistic conditions on humans susceptible to yawn contagion by Norscia et al (2016a,b) when considering a larger dataset that included yawns that could be seen by the potential responder
Summary
Yawning is an involuntary sequence of mouth opening, deep inspiration, brief apnea, and more or less slow expiration (Baenninger, 1997; Walusinski and Deputte, 2004; Guggisberg et al, 2010; Krestel et al, 2018). It has been defined as a stereotyped or reflex-like pattern (Lehmann, 1979; Provine, 1986). Being a physiological response, yawning can be affected by internal and external factors such as the time of the day (Giganti and Zilli, 2011) or intracranial/brain temperature (Gallup and Eldakar, 2013). In human and nonhuman primates, depending on the species, when yawning is shown to others, it can communicate threat (Troisi et al, 1990; Deputte, 1994) and/or physiological and behavioral changes (Provine et al, 1987; Leone et al, 2015; Zannella et al, 2015). Yawn contagion can be elicited even if the yawn is heard but not seen (Arnott et al, 2009; Massen et al, 2015)
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