Golden years. Seniors from the 1936 Lothian Birth Cohort gathered for a reunion this past April.

Golden years. Seniors from the 1936 Lothian Birth Cohort gathered for a reunion this past April.

Douglas Robertson/CCACE

Slow visual processing may lower IQ as we age

Old age may make us wiser, but it rarely makes us quicker. In addition to slowing down physically, most people lose points on intelligence tests as they enter their golden years. Now, new research suggests the loss of certain types of cognitive skills with age may stem from problems with basic sensory tasks, such as making quick judgments based on visual information. Although there’s no clear causal link between the two types of thinking yet, the new work could provide a simple, affordable way to track mental decline in senior citizens, scientists say.

Since the 1970s, researchers who study intelligence have hypothesized that smartness, as measured on standard IQ tests, may hinge on the ability to quickly and efficiently sample sensory information from the environment, says Stuart Ritchie, a psychologist at the University of Edinburgh in the United Kingdom. Today it’s well known that people who score high on such tests do, indeed, tend to process such information more quickly than those who do poorly, but it’s not clear how these measures change with age, Ritchie says.

Studying older people over time can be challenging given their uncertain health, but Ritchie and his colleagues had an unusual resource in the Lothian Birth Cohort, a group of people born in 1936 whose mental function has been periodically tested by the Scottish government since 1947—their first IQ test was at age 11. After recruiting more than 600 cohort members for their study, Ritchie and colleagues tracked their scores on a simple visual task three times over 10 years, repeating the test at the mean ages of 70, 73, and 76.

The participants—all of whom had normal or, thanks to glasses or contacts, corrected-to-normal vision—sat before a computer and watched as two lines of different lengths flashed before their eyes. Joined by a single horizontal line at the top of the screen, this asymmetrical “n” shape appeared for a randomly assigned amount of time, sometimes as few as 6 milliseconds. The participants’ only job was to choose whether the longer line had appeared on the left or the right side of the shape by pushing a button. They were allowed to take as long as they wished to deliberate, Ritchie explains. (So boring was the 30-minute task that the elderly participants “groaned like hell” at its mention during the recent Lothian cohort reunion pictured above, he says.)

Next, Ritchie and colleagues compared the amount of time it had taken for participants to make their choices, called inspection time, and examined how it tracked with their performance on four standard intelligence tests. All focused on solving problems based on novel information: For example, one test required recreating a visual pattern with colored blocks, while another required participants to listen to a list of numbers and recite them backward. Over time, the decline in participants’ scores on the intelligence tests was strongly correlated with an increase in their inspection times, suggesting that it might be possible to use the simpler task as a proxy for more complicated intelligence tests in hard-to-reach elderly populations, the scientists report today in Current Biology.

The results strengthen the hypothesis that the complex intelligence we associate with geniuses like Albert Einstein may actually be driven by very simple processing skills in vision, hearing, and other senses, says John Gabrieli, a neuroscientist at the Massachusetts Institute of Technology in Cambridge who wasn’t involved with the research. As we age, our brains may become like “an extremely slow computer that can’t run more complicated operations,” he says. More research is needed to establish whether loss of visual processing speed actually leads to slower higher level thinking, but if it does, it might be possible to help 70-year-olds maintain intelligence by training them to make these simple visual judgments faster, he says. That’s easier said than done, however, Ritchie notes. One of his colleagues tried to improve his performance on the task over the course of 100 days, but “stopped getting better on the second day”—which doesn’t bode well for the test’s usefulness as a brain-training exercise.