OUR sight is sharpest at dawn and dusk聽鈥� and now we may know why. It聽is聽not a result of changes within our eyes, but of how the brain processes visual signals.
The brain has continual background activity. But this lessens in the visual centres around sunrise and sunset, which may improve our perception of聽visual information in the聽low light聽levels at these times.
Advertisement
鈥淵ou are sensitising your brain,鈥� says of Goethe University in Germany. 鈥淎 weak signal聽coming in will have a higher signal-to-noise ratio.鈥�
Our eyes adapt to dim light in several ways, such as by the pupils dilating to let in more light rays. But聽irrespective of light levels, our eyesight gets better around the times of dawn and dusk. This has even been seen in people who lived for long periods in聽underground bunkers, cut off from natural light.
To find out why, Kell鈥檚 team asked 14 men to spot when dim crosshairs flashed up on a screen at six different times of day. They also had their brains scanned, both as they did the task and while they rested.
There were two noticeable peaks in their performance on the visual test: at 8.00 am and 8.00 pm, roughly corresponding to the time of sunrise and sunset (Nature Communications, DOI: 10.1038/s41467-018-03660-8).
At these times, there was also a fall聽in background activity in three brain areas that process information from the eyes, ears and sense of touch. 鈥淲e聽see a sensitisation of all the sensory areas of the brain,鈥� says Kell. He thinks that is because people are more reliant on their vision and other senses in dim light.
鈥淧re-industrial tribes are very active during dawn and dusk, which means they are also in danger from animals then,鈥� says Kell. This could explain why we evolved to have sharper senses at these times.
Read more: Good looking: The veggies that really do boost night vision
[video_player id=鈥漞XHJnwJR鈥� access_level=鈥漵ubscriber鈥漖
This article appeared in print under the headline 鈥淲hy we have better eyesight at twilight鈥�
