Page 141 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Evidence for yawn contagion in orangutans
Specifically, we found a significant contrast of yawns between the yawn and control condition in the familiar (b = 6.62, SE = 1.59, p < 0.001) and unfamiliar trigger (b = 3.45, SE = 1.52, p = 0.023), but not in the avatar trigger (b = 0.09, SE = 1.58, p = 0.950) (Figure 3). Hence, orangutans are more likely to yawn in response to yawning videos rather than to control videos, but only when the yawning individual is a “real”orangutan (i.e., a familiar or unfamiliar conspecific), and are less likely to yawn in response to the avatar. To investigate whether the likelihood of CY differed with regard to familiarity with the “real” orangutan stimuli, we also ran an additional binomial model on a reduced dataset that excluded all trials with the avatar (see supplemental materials). Whereas this model confirmed the previously found effect of condition, here we did not find a significant interaction between condition and familiarity, suggesting that the likelihood of CY was not being modulated by the familiarity with the “real” orangutan. We also investigated the effect of familiarity on yawning rate using the same reduced dataset, but the model including the interaction between condition and trigger did not significantly improve the null model (c2(3)=3.50, p=0.321). As such, while we can establish that orangutans do show CY in response to yawn videos of familiar and unfamiliar conspecifics, this likelihood of CY is not modulated by familiarity and we cannot draw any conclusions regarding the strength of CY in relation to familiarity.
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Figure 3. Likelihood of yawning across conditions and triggers. Boxplots show the median (solid line), 25th- 75th percentile (box) and the largest and smallest value within 1.5 times the interquartile ranges respectively (whiskers). Dots reflect outliers.
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