Visual processes 'critical for sharp mind'
Scientists say they have uncovered a basic process that may help explain why some people's thinking skills decline with age.
Research indicates as individuals begin to have difficulties interpreting simple images, their overall intelligence falls too.
Psychologists suggest this ability to glean information at a glance may play a critical role in how we deal with more complex tasks.
The study appears in Current Biology.
Psychologists from the University of Edinburgh studied 600 healthy 70-year-olds for six years.
Each took a series of tests designed to check complex thinking skills and compare these with how accurately they could process simple visual information.
Intelligence tests included memorising lists of numbers and then repeating them backwards and sorting words into alphabetical order before reciting them.
To measure visual processing, participants watched a computer screen as two different sized shapes flashed up.
Some images appeared for as few as six milliseconds while others were present for up to 200 milliseconds.
They were asked to correctly identify the shape with the longest edge.
As people got older, their ability to do well in this task decreased.
And the worse their scores on the visual processing tests, the worse they did in more complex intelligence tasks.
Dr Stuart Ritchie, a lead researcher in the study, said: "The results suggest the brain's ability to make correct decisions based on brief visual impressions limits the efficiency of more complex mental functions.
"Since the declines are so strongly related, it might be easier under some circumstances to use the shape test to chart a participant's cognitive decline than it would be to sit them down and give them a full, complicated battery of IQ tests."
Dr James Thompson, of University College London, who was not involved in the research, told the BBC: "This is important work.
"We know older people's mental processes start to slow over time. But we don't know exactly why this happens.
"This research makes us question whether the reason we start to slow up in old age is because the speed at which we apprehend the world slows down."
Scientists say these types of cognitive skills are important in everyday activities such as making decisions regarding money.
"As our population ages it is will be increasingly important to understand the basic mechanisms behind these changes in intelligence.," Dr Ritchie told the BBC