New findings helped researchers gain insight into why some people's thinking skills decline with old age, and how that relates to lower visual perception speed.
The longitudinal study, published in the August 4 edition of Cell Biology, is one of the first to test the idea that changes in what is known as "inspection time" could be related to declines in intelligence occurring in old age.
To make their findings the researchers showed 600 healthy older people flashes of two shapes on a screen and measured the time it took them to distinguish one from the other. This test was repeated when the participants were at the ages of 70, 73, and 76.
"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," said 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."
Past studies have shown people with higher IQs tend to be better at distinguishing between two fleeting shapes, but before now nobody had looked at how this changed as people got older.
"What surprised us was the strength of the relation between the declines," Ritchie said. "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."
The results suggest the slowing of the visual decision-making process may be behind the decline of complex decision making commonly recognized as general intelligence. The findings could also find a practical use for the inspection time measure since the test can easily be taken on a computer and is appropriate for people of most ages and mental capacities.
"Since the declines are so strongly related, it might be easier under some circumstances to use inspection time 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," Ritchie concluded.
