The loss of intelligence as we get older may be caused in part by deteriorating vision.
UK and US researchers have found people’s ability to absorb information from a fleeting glance worsened as they aged, and was related to a decrease in more complex mental functions.
The evidence comes from experiments, reported in the journal Current Biology, in which 600 healthy older people were shown very brief flashes of one of two shapes on a screen. The time it took each of them to reliably tell one from the other was measured.
Participants repeated the test at ages 70, 73, and 76. The longitudinal study is among the first to test the hypothesis that the changes they observed in the measure known as inspection time might be related to changes in intelligence in old age.
“The results suggest that the brain’s ability to make correct decisions based on brief visual impressions limits the efficiency of more complex mental functions,” says Stuart Ritchie of the University of Edinburgh.
“As this basic ability declines with age, so too does intelligence. The typical person who has better-preserved complex thinking skills in older age tends to be someone who can accumulate information quickly from a fleeting glance.”
Previous studies had shown that smarter people, as measured by standard IQ tests, tend to be better at discerning the difference between two briefly presented shapes. But before now no-one had looked to see how those two measures might change over time as people grow older. The findings were unexpected.
“What surprised us was the strength of the relation between the declines,” Ritchie says. “Because inspection time and the intelligence tests are so very different from one another, we wouldn’t have expected their declines to be so strongly connected.”
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