You can tell when someone is being rude and not listening by looking at their eyes, scientists have shown.
A study suggests that when a person blinks, it is a sign that their mind is wandering.
Blinking is thought to set up tiny physical barriers that help to shut off the outside world.
Researchers in Canada were inspired by studies showing that when attention falters, parts of the brain that process external influences are less active.
"We thought, OK, if that's the case, maybe we'd see that the body would start to do things to prevent the brain from receiving external information," said neuroscientist Dr Daniel Smilek, from the University of Waterloo in Ontario.
"The simplest thing that might happen is you might close your eyes more."
To test the theory, 15 volunteers were asked to read from a book on a computer screen while a sensor tracked their eye movements, recording any blinks.
Whenever the computer beeped at random intervals, the scientists checked to see if the participants were focused on reading.
The volunteers were found to blink more when their minds were wandering than when they were paying attention.
"What we suggest is that when you start to mind-wander, you start to gate the information even at the sensory endings - you basically close your eyelid so there's less information coming into the brain," said Dr Smilek.
The research is reported in the journal Psychological Science.Reuse content