The study suggests a decline in intelligence later in life is linked to a decline in the brain's ability to interpret what the eye sees.
The researchers, from the University of Edinburgh in the UK, have published their findings in the journal Current Biology.
"One of the major problems facing clinicians and health care workers is monitoring how cognitive decline is occurring as we age, particularly in those with dementia," says Prof. James Goodwin, head of research at Age UK, a national charity for older people.
Dr. Stuart Ritchie - lead study author from the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology - and colleagues say their tests suggest that a decline in intelligence later in life is linked to a decline in visual processing efficiency, which is the brain's ability to interpret what the eye sees.
To conduct their study, they tested over 600 people for visual processing at ages 70, 73 and 76. Study participants were part of the Lothian Birth Cohort 1936, a group of people born in 1936 and who took part in the Scottish Mental Survey of 1947. During the course of the survey, the individuals were tested on changes in reasoning, memory, thinking speed, fitness, eyesight, blood composition and genetics.
The researchers used a test that flashes one of two shapes on a screen, which measured how long each person needed in order to accurately distinguish one shape from the other.
Next, the team compared the visual test results with intelligence tests taken by the study participants at the same ages.
'A fleeting glance'
Results show that intelligence levels decreased as the brain's ability to make accurate conclusions based on visual information declined.
The team says their findings suggest that declines in visual processing could be part of a wider slowing in complex decision making, which is linked to general intelligence.
Commenting on their findings, Dr. Ritchie says:
"The results suggest that the brain's ability to make correct decisions based on brief visual impressions limits the efficiency of more complex functions. As this basic ability declines with age, so too does general intelligence. The typical person who has better-preserved complex thinking skills in old age tends to be someone who can accumulate information quickly from a fleeting glance."
His colleague, Prof. Ian Deary, says it is important to understand why some people's thinking skills are better in older age than others'.
Though he notes that they tried to isolate a process involved in age-related mental decline in this study, in future research they will endeavor to "find the brain structures, health factors and any lifestyle habits that support the retaining of both efficient visual processing and general intelligence."
Prof. Goodwin adds that though this study is "an important breakthrough which will, in time, be of huge benefit to older people," more research is needed.
Yesterday, Medical News Today reported on a study that suggested eating baked or broiled fish every week is good for the brain, regardless of omega-3 fatty acid content.