Page 147 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Evidence for yawn contagion in orangutans
in captivity, although its presence was not shown in our sample. Yet, given our small sample size, replications that test for the presence and subsequent direction of social modulation of CY in orangutans are needed.
Finally, we could not quantify attention to the screen, which is one of the common methodological issues raised by Massen et al. (2017). We tried to maximize attention to the screen by using attention-grabbing videos of caretakers at the start of every video sequence, and by adding colored screens in-between stimulus presentations. Furthermore, we made sure that orangutans had a direct line of sight towards the screen at the start of the experiment, and only recorded yawns when they directed their attention to the screen at least once during stimulus presentation. Nevertheless, quantification of attention to the stimuli (either measured as a continuous variable or a frequency of gazes) remains the most robust way to control for potential effects of attentional bias.
To summarize, our findings contribute to understanding the evolutionary basis of CY in hominids by showing that orangutans, like humans, chimpanzees and bonobos, yawn contagiously.
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