Published in Royal Society’s Biology Letters, the study combines machine learning and listener experiments to uncover the distinct characteristics of tickling-induced laughter and its evolutionary roots.
Roza Kamiloglu scoured with her colleagues YouTube for videos capturing authentic, spontaneous laughter and compiled a dataset of 887 laughs from real-life scenarios. These videos were carefully selected to ensure they featured clear, unposed laughter and were categorized into four distinct eliciting contexts: tickling, humorous stimuli (such as comedy sketches or funny movies), witnessing someone’s misfortune, and verbal jokes. To maintain the integrity of the dataset, each video had to meet strict inclusion criteria, ensuring the laughter was genuine, unambiguous in its context, and produced by a single individual.
The researchers employed machine learning techniques to identify systematic acoustic differences between the laughter types. The system accurately classified laughter as tickling-induced in 62.5% of cases, while its performance for distinguishing other types of laughter hovered only slightly above chance. Listener experiments further validated these findings: in one study, participants were asked to identify whether laughs originated from tickling or other contexts, achieving significantly above-chance accuracy. In another study, participants rated laughter clips on perceptual dimensions like arousal, positivity, and vocal control, revealing that tickling-induced laughter was consistently perceived as more arousing and less controlled than other types.
Kamiloglu explains, “This type of laughter likely originated over ten million years ago, rooted in the social play behaviors of our common ancestors with the primates. Just like chimpanzees who chuckle during playful wrestling matches, or dogs who pant excitedly during a game of chase, this laughter is a spontaneous burst of joy, deeply ingrained in our biology." Its distinct acoustic features reflect an automatic, less controlled response, setting it apart from laughter triggered by more cognitively complex stimuli.”
The findings reveal how tickling-induced laughter, a deeply ingrained biological response, provides a fascinating glimpse into the evolutionary origins of human vocal expressions. Even individuals who have never heard a laugh, such as those born profoundly deaf, exhibit remarkably similar laughter patterns, highlighting the innate nature of this response. By highlighting its unique role in playful interactions, the study underscores laughter's enduring significance in social bonding across species and time.