Yawning to communicate? Yawn exposure increases both threat detection and subjective sleepiness

Yawning is widely observed in daily life. But its function has largely remained less explored. In the current study, we examined how yawning exposure affected threat detection in human adults and its potential mechanisms. We recruited 96 participants and manipulated the yawning exposure by letting participants viewing yawn videos or listening to yawn audios. Then they were asked to complete a threat-detection task as well as measures of subjective sleepiness and theory of mind (ToM). Results revealed that yawning exposure significantly enhanced both the speed and accuracy of detecting snakes from frogs but not vice versa in the visual modality (yawning videos exposure). In contrast, within the auditory modality (yawning audios exposure), yawning exposure also improved detection accuracy (rather than reaction time) for non-threatening frogs, indicating a possible modality-dependent pattern rather than a universal threat-specific enhancement. Besides, individual differences in ToM capacity likely played a role in the relationship between yawning exposure and threat detection: participants with higher ToM scores exhibited greater sensitivity in identifying snakes under the yawning condition, suggesting that the ability to infer others' mental states might be critical for interpreting the informational content of yawning. Furthermore, yawning exposure increased subjective sleepiness and the increase in subjective sleepiness did not correlate with threat detection performance, indicating that the observed effects likely arise from domain-specific cognitive processes rather than generalized arousal modulation. These findings provided support for the communicative function of yawning and underscored the interplay between evolved nonverbal signals and modern cognitive capacities like ToM.