Scientists have long known that when our brains are focused on a task we can fail to see other things in plain sight, a phenomenon known as "inattentional blindness."
But researchers at University College London have found a person's visual field does not need to be cluttered with other objects to cause this "blindness" and that focusing on remembering something we have just seen is enough to make us unaware of things going on around us, Britain's Wellcome Trust, which supported the research, reported.
"An example of where this is relevant in the real world is when people are following directions on a sat nav [global positioning system device] while driving," study leader Nilli Lavie said.
"Our research would suggest that focusing on remembering the directions we've just seen on the screen means that we're more likely to fail to observe other hazards around us on the road, for example an approaching motorbike or a pedestrian on a crossing, even though we may be 'looking' at where we're going."
Lavie calls competition in the brain for limited information processing power "load theory," and that too much information can bring on "load induced blindness."
The study suggests competition in the brain between new visual information and our short-term visual memory that was not appreciated before, the researchers said.
"The 'blindness' seems to be caused by a breakdown in visual messages getting to the brain at the earliest stage in the pathway of information flow, which means that while the eyes 'see' the object, the brain does not," she said.