Researchers pinpointed the "physical limit" of personal space invasion.
A new study allowed the researchers to "define the limits" of peripheral space (space surrounding the body), a University College London press release reported.
The distance varied within certain limitations, depending on the individual's anxiety level. Comfortable distances range from about seven to 15 inches.
Researchers analyzed 15 people between the ages of 20 and 37. The team administered an electric stimulus to a nerve in the subjects' hands that is known to trigger blinking. The hand-blink reflex (HBR), is not controlled by the brain.
To test a person's required personal space, researchers observed the blink reflex ("a defensive response to potentially dangerous stimuli") when a stimuli (their own hand) was introduced at varied distances.
When the team compared the blink reflex data with information from self-assessed anxiety surveys, they found people who scored high on the stress test had a stronger reaction to stimuli presented seven inches away from their face than those with lower scores.
People who had a stronger reaction to more distant stimuli were classified as having a large "defensive peripersonal space" (DPPS).
"This finding is the first objective measure of the size of the area surrounding the face that each individual considers at high-risk, and thus wants to protect through the most effective defensive motor responses" lead author Dr Giandomenico Iannetti, of UCL Neuroscience, Physiology and Pharmacology, said.
The researchers hope the study's conclusions will lead to a method of measuring anxiety levels and defensive behavior. These tests could be used to determine the reliability of candidates for high-stress jobs, such as firefighters and police.
Personal space sensitivity is a natural defense against perceived dangers, but breaking the barrier could be important in relationships, NBC reported.
"You show how much you are comfortable with [your partner] by how much you're willing to shrink your personal space, sometimes down to nothing," Michael Graziano, a researcher at Princeton University who wasn't involved in the study, told NBC.
