Sci. Aging Knowl. Environ., 9 February 2005
The Better to See You With
Older folks surpass youngsters in discerning one kind of motion
Wisdom may increase with age, but vision typically deteriorates. However, new work suggests that one visual ability improves: detecting the movement of certain types of patterns. The counterintuitive outcome might stem from a communication breakdown between visual neurons.
Aging hammers the eye; often lenses cloud, and retinal cells degenerate. How neurons process visual information captured by the eye also changes over time. In older monkeys, for example, cells in the brain's visual cortex are worse than young monkeys' neurons at discerning the orientation of a pattern. However, other findings inspired neuroscientist Patrick Bennett of McMaster University in Hamilton, Ontario, and colleagues to hypothesize that aged vision might be keener under specific conditions. In one study, vision scientist Joseph Lappin and colleagues at Vanderbilt University in Nashville, Tennessee, asked young people to determine which way a grill pattern moved on a computer screen. The team found that if the contrast between the bars and the background was low, increasing the pattern's size made it easier to discern the direction. But if the bars stood out, viewers found it harder to pick out the motion of a large pattern than of a small one.
This result reflects interactions among visual neurons, the researchers conjectured. Each neuron responds to a section of the visual field, and a small image probably falls within one section. But larger images stimulate surrounding cells. Earlier research has shown that, in certain parts of the visual system, these neurons can inhibit the neuron at their center. In young people, presumably, dueling cells interfere with perceiving a large grating's motion. However, other studies have shown that neurons in older animals are less likely to meddle with their neighbors. Bennett and colleagues reasoned that seniors might be better than young people at detecting motion of a large pattern.
The researchers tested their idea on people between 18 and 32 and folks in their 60s and 70s. They altered the size and contrast of the grill and timed how long each person took to decide which way the stripes were traveling (see video clips). When the researchers enlarged a high-contrast pattern, older folks' ability to perceive its motion remained about the same as for smaller patterns. Youngsters, in contrast, took almost twice as long to choose compared to the small image, often responding more slowly than older subjects. At least at this task, Bennett says, age improves performance. Practically speaking, the difference might mean that a young person would excel at detecting a moving object in a complex scene, such as following one hockey player in a game, he says. But seniors would shine at perceiving the overall pattern of movement, such as tracking the action from one end of the rink to the other.
Lappin praises the study for documenting "a previously unknown effect of aging on vision." Seniors might not want to celebrate, though. "The bad news is that this probably comes at the cost of deficits in some other aspect of visual perception," he says. Acute vision, like wisdom, doesn't come cheap.
February 9, 2005
Science of Aging Knowledge Environment. ISSN 1539-6150