How close can something get to your face before you blink? That’s basically the method scientists use to determine “defensive peripersonal space,” the safety bubble of personal space around the body. When something potentially threatening enters that bubble, we instinctively want to defend ourselves.

According to new research, for most people, that personal bubble is about 20 to 40 centimeters away from the face. The more anxious you are, though, the bigger safety bubble you want.

Scientists from the Department of Neuroscience, Physiology and Pharmacology at University College London monitored 15 subjects as they held their own hands in front of their faces at distances of 4, 20, 40 and 60 centimeters. An electrical stimulus applied to a nerve in each subject’s wrist prompted a blink, a subconscious defensive response, the intensity of which was measured by electrodes on the surface of the eyelid. The larger the reflex response, the more dangerous the person perceived the stimulus.

Hand-Blink Reflex

The closer the hand got to the face, the greater the EMG (electrical impulse response) was.

In this case, people who scored higher on an anxiety test reacted more strongly to stimuli 20 centimeters away from their face, compared to less anxious participants. The researchers hypothesize that more anxious individuals possibly perceive threats as closer than non-anxious individuals do. But of course, with this small of a sample size, it’s hard to say anything with great certainty.

“This finding is the first objective measure of the size of the area surrounding the face that each individual considers at high-risk,” lead author Giandomenico Iannetti said. The authors suggest that this could be used to develop measurement tests for people’s ability to assess risks, especially in potentially dangerous professions like firefighting.

For the full study, see The Journal of Neuroscience.