Even when we're not tired, why do we yawn if someone else does?
Experts at the UK's University of Nottingham have published research that suggests the human propensity for contagious yawning is triggered automatically by primitive reflexes in the primary motor cortex - an area of the brain responsible for motor function.
Their latest findings show that our ability to resist yawning when someone else near us yawns is limited. And our urge to yawn is increased if we are instructed to resist yawning.
But, no matter how hard we try to stifle a yawn, it might change how we yawn but it won't alter our propensity to yawn.
Importantly, they have discovered that the urge to yawn - our propensity for contagious yawning - is individual to each one of us.
Said study leader Professor Stephen Jackson: "We suggest that these findings may be particularly important in understanding further the association between motor excitability and the occurrence of echophenomena in a wide range of clinical conditions that have been linked to increased cortical excitability and/or decreased physiological inhibition such as epilepsy, dementia, autism, and Tourette syndrome."
Contagious yawning is triggered involuntarily when we observe another person yawn.
It's a common form of echophenomena - the automatic imitation of another's words (echolalia) or actions (echopraxia).
And it's not just humans who have a propensity for contagious yawning - chimpanzees and dogs do it too.
Echophenomena can also be seen in a wide range of clinical conditions linked to increased cortical excitability, or decreased physiological inhibition such as epilepsy, dementia, autism and Tourette syndrome.
Yet the neural basis for echophenomena is unknown.
To test the link between motor excitability and the neural basis for contagious yawning, the research team used an approach called transcranial magnetic stimulation (TMS).
They recruited 36 adults, who viewed video clips showing someone else yawning and were instructed to either resist yawning or to allow themselves to yawn.
The participants were videoed throughout, and their yawns and stifled yawns were counted.
The intensity of each participant's perceived urge to yawn was continuously recorded.
Using electrical stimulation, they were also able to increase the urge to yawn.
"This research has shown that the urge is increased by trying to stop yourself," study co-leader Professor Georgina Jackson said.
"Using electrical stimulation we were able to increase excitability and in doing so increase the propensity for contagious yawning.
"In Tourettes, if we could reduce the excitability, we might reduce the ticks and that's what we are working on."
Kiwi's book explores 'reproductive horror'
What is gynaehorror?
The Kiwi pop culture expert who coined the term describes it as a rather specific sub-genre of horror films concerned with all aspects of female "reproductive horror", from virginity and pregnancy to motherhood and menopause.
"Think classic films like Rosemary's Baby or The Brood or even the Alien series, or more recent films like The Witch and The Babadook," said Dr Erin Harrington, a lecturer in English and cultural studies at the University of Canterbury's College of Arts.
"Horror films are a great social barometer as they engage with and often directly invoke culturally specific and contemporaneous fears and anxieties.
"Engaging with these films, as with other forms of popular culture, can help us understand and interrogate taken-for-granted ideas about what it is women 'should' do and be."
Harrington has now written an academic book about the broader concept, featuring an in-depth analysis of the portrayal of women in horror films from the 1960s until the present day, and covering topics ranging from "psychobiddies, grande dames and horrific harridans" to virgins and vagina dentata.
Titled Women, Monstrosity and Horror Film, it makes a unique contribution to the study of women in horror film specifically, while providing new insights in the broader area of popular culture, gender and film philosophy.
"Women occupy a privileged place in horror film," Harrington said.
"Horror is a space of entertainment and excitement, of terror and dread, and one that relishes the complexities that arise when boundaries - of taste, of bodies, of reason - are blurred and dismantled."
It's familiar ground for Harrington, whose academic work focuses on horror, embodiment, popular and visual culture, and sex and gender, and she also has a particular interest in theatre, criticism and dramaturgy.
How robots can behave like pedestrians
Just as drivers observe the rules of the road, most pedestrians follow certain social codes when navigating a hallway or a crowded thoroughfare: keep to the right, pass on the left, maintain a respectable berth, and be ready to weave or change course to avoid oncoming obstacles while keeping up a steady walking pace.
Now US engineers at MIT have designed an autonomous robot with "socially aware navigation," that can keep pace with foot traffic while observing these general codes of pedestrian conduct.
In drive tests performed inside MIT's Stata Centre, the robot, which resembles a knee-high kiosk on wheels, successfully avoided collisions while keeping up with the average flow of pedestrians.
To make its way autonomously through a busy environment, the robot had to solve four main challenges: localisation (knowing where it is in the world), perception (recognising its surroundings), motion planning (identifying the optimal path to a given destination), and control (physically executing its desired path).
Yu Fan Chen and his colleagues used standard approaches to solve the problems of localisation and perception. For the latter, they outfitted the robot with off-the-shelf sensors, such as webcams, a depth sensor, and a high-resolution LIDAR sensor.
For the problem of localisation, they used open-source algorithms to map the robot's environment and determine its position.
To control the robot, they employed standard methods used to drive autonomous ground vehicles.
"Socially aware navigation is a central capability for mobile robots operating in environments that require frequent interactions with pedestrians," said Chen, who led the work.
"For instance, small robots could operate on sidewalks for package and food delivery.
"Similarly, personal mobility devices could transport people in large, crowded spaces, such as shopping malls, airports and hospitals."