BioEd Online

As people grow older, their vision can actually get better in some ways, according to a Canadian study. The findings suggest that neurological changes could help the elderly to spot small motions in otherwise uniform scenes.

Part of visual processing in the human brain involves cells that suppress each other's activity. This allows the mind to focus on a scene's important features while ignoring trivial regions. But as people age, these inhibitory interactions seem to weaken.

To explore the effects of this change, researchers tested people between 18 and 31 years old, and others aged 60 and above. Subjects viewed a computer screen showing moving, vertical black-and-white stripes. They then had to decide in which direction the bands were travelling.

Prompt perspective

Previous studies have shown that, as the number of stripes in view increases, young people become much worse at identifying their movement. Scientists think that the stripes' large, stark borders activate the brains inhibitory mechanisms. The mind starts disregarding these monotonous forms.

Vision expert Patrick Bennett of McMaster University in Hamilton, Ontario and his colleagues wanted to know if older people showed the same drop in performance. To the researchers' surprise, they did not.

With a large part of the screen filled with the high-contrast stripes, younger people required 100 milliseconds to work out the direction of movement, and took twice as long for a small patch. But the performance of older people stayed constant at around 70 milliseconds.

"That's a very odd result because in many, many tasks you find that older people require more time. It's an exception to the rule," says Bennett. Reduced brain inhibition might make older observers more sensitive to visual input that is normally suppressed, he says. The team reports its results in Neuron¹.

It is the high contrast between black and white stripes that produces this effect, and not the expanding area on the screen showing the stripes. Both young and older people are faster at identifying the movement of low-contrast grey stripes when they can see more of them.

The big picture

So might this be an advantage in the real world? Bennett speculates that older people might find it easier to follow action in sweeping scenes, such as a sporting event. "If you're watching a football match, you look at the flow of the players up and down the field. That part might be easier for older people."

At the moment, however, he and his fellow researchers simply aim to pinpoint where the related inhibitory pathways act in the brain.