How scientists uncovered the invisible balloon around your head

A study has discovered the balloon-like nature of our personal space which has evolved to protect us from threats above. 

NS

Sign Up

Get the New Statesman's Morning Call email.

Before you even know where the wasp is, you flinch. Each of us has this space around our bodies that is extremely sensitive to external stimuli.  It's an evolutionary advantage to be hyper-alert to threats nearby as they're more likely to cause you harm, a lot sooner. 

Researchers at University College London have found that this space, at least for humans, is like “a child’s balloon - it sticks up regardless of one’s posture”. 

Utilising a reflex called the hand-blink-reflex, the scientists imaged this personal space in different conditions. 

The experiment consisted of asking the participants to stand upright and then electrically stimulating a nerve in the right wrist, while the same hand was placed a few centimetres from the participant's nose. The hand was then placed in ten different equally-spaced angles from above the head, to below the chin. 

The reseachers could then measure the participant’s personal space by recording the increase in their blink reflex. The hand-blink-reflex is a defensive reflex which increases the closer the hand being stimulated is to the participant's face. The more the participant blinked, the more sensitive their personal space was in that area. The space could then be imaged as a geometric model using the data they collected. 

This experiment was repeated with the participant lying on his or her back and lying sideways. The researchers found that the larger end of the space was always at the top - like a balloon which always flaoats the same way up -  and concluded that the brain "continuously updates the threat value of stimuli based on gravitational cues". 

There is an obvious evolutionary advantage to being aware of threats from above - gravity causes objects to fall. In other words, the no.1 priority for the human brain is avoiding being squashed from above. 

Some animals have a more evolved personal space than us. Professor Gian Domenico Iannetti, who conducted the experiment with Dr Rory Bufacci, is currently experimenting on mice using virtual reality. Mice in particular have very developed personal spaces and are known to run towards their nest immediately at the onset of a shadow growing above them. More research needs to be done on other animals to determine if gravity is also important to their evolved sense of security. 

Iannetti points out that some animals, like snakes, are more likely to receive their threats from below and so may have a personal spaces that have developed completely differently to us. 

As for humans, the research shows the remarkable ability of the brain to calculate physical laws automatically. The question for 21st century scientists is not why the apple fell, but how much Isaac Newton flinched. 

Jason Murugesu is a postgraduate student in science communication at Imperial College London, and a former Wellcome Scholar at the New Statesman.

Free trial CSS