Silent reading is far from silent in your brain. Deep within your head there is a voice reading aloud each word as your eyes pass over it.

Let’s do a seemingly unrelated experiment first. Turn on your television and radio. Try to understand both the words from the television and the radio simultaneously. You might have noticed understanding one source required ignoring the other, and you could feel your attention shifting between the two voices. Although we can listen to multiple people speaking at the same time, we can only truly understand one person speaking at a time.

There are three major areas that allow you to understand spoken word. The first is the Auditory Cortex (听觉皮层), which processes the pure characteristics of incoming sounds. Both sides of your brain contain this region. The next area is the Broca/Wernicke (B/W) network, which makes sense of the spoken word. This network exists in only one side of your brain. This means that, although the sounds of language are initially processed in both sides of the brain, spoken word must eventually be funneled (流经漏斗) into this single network. This quickly leads to a bottleneck, which is controlled by the third area: the left Inferior Frontal Gyrus (IFG, 额下回). When you try to understand two people speaking at the same time, this region effectively blocks one voice while it allows the other to pass through the B/W bottleneck. Any information that does not immediately make it through the B/W network disappears completely — there is no waitlist.

Now, let’s bring all the pieces together to see why it’s related to your silent reading. When you read, the first region to demonstrate activation is the Visual Cortex, which processes the pure visual characteristics of incoming sights. Immediately after the visual cortex activates, the speech areas of the brain fire up because your brain processes your silent reading in a manner almost identical to the way in which it processes an actual, out-loud speaking voice. For this reason, attempting to read while listening to someone speak is the same as trying to understand two people speaking at the same time—it can’t be done!

Note: disappear; wait

A．	B．
C．	D．

One of the greatest mysteries in science is just how Earth went from a planet with minimal oxygen to the breathable air we have now. Scientists long figured that cyanobacteria (蓝细菌) were involved, but couldn’t tell what started the great oxygen-producing cycle.

A new study published in Monday’s Nature Geoscience may provide the key. It theorizes that Earth’s gradually lengthened day from six hours to the current 24 hours kick-starts cyanobacteria into producing lots of oxygen, making most of life as we know it possible. Here are the takeaways of the study.

About 2. 4 billion years ago, there was so little oxygen in Earth’s atmosphere that it could barely be measured, so no animal or plant could live. Instead, lots of bacteria breathed in CO₂, and in the case of cyanobacteria, produced oxygen in the earliest form of photosynthesis (光合作用).

At first it wasn’t much. But in about 400 million years, as Earth’s rotation (旋转) gradually slowed down and the day was lengthened from six hours to the present 24 hours, the cyanobacteria breathed more and more oxygen into Earth’s atmosphere until it reached one-tenth the amount of oxygen we have now. The increased oxygen allowed plants to join in the oxygen-making party.

The authors of the study put their theory to test with the bacteria found on a 24-meter-deep seabed in Lake Huron. They exposed the smelly bacteria, which are very similar to the cyanobacteria living around 2. 4 billion years ago, to varying amounts of light, and found that the more continuous light the bacteria got, the more oxygen they produced.

“What makes the idea so convincing is that it doesn’t require any big biological changes in bacteria or the world’s oceans,” said Tim Lyons, a professor at the University of California, Riverside, who wasn’t part of the research team. “This may be a simple but plausible explanation for Earth’s oxygen increase.”

Blue light before bedtime can make it harder to sleep, and the screens on phones, computers and televisions give out plenty of blue light. This is all true. But if you consider blue light as a major problem affecting your sleep or your eye health, it’s time to change your mind.

Philip Yuhas, a professor of optometry (验光), writes at The Conversation, “Blue light isn’t a uniquely technological evil. It’s part of sunlight, and your eyes are exposed to plenty of it all the time. You’re fine.” The pigments (色素) and the lenses of our eyes actually block blue light fairly well—so in a sense, we already have built-in blue-blocking protection.

Adding more protection isn’t likely to help, though. You can buy glasses and screen filters (过滤器) that block blue light, but Yuhas points out they are probably a waste of money. He says, “The products that my patients ask about do not block out much blue light.” The leading blue-blocking anti-reflective coating, for example, blocks only about 15% of the blue light that screens give out.

You could get the same reduction just by holding your phone another inch from your face. Try it now and see if you notice a difference. No? Then it shouldn’t surprise you that a recent analysis concluded that blue-blocking glasses and coatings have no significant effect on sleep quality, comfort at the computer or retinal (视网膜的) health.

The American Academy of Ophthalmology doesn’t recommend blue-blocking products, either. Instead, if you’re concerned about your eye health or your ability to get into sleep on time, you already know what to do: Put the screens away at bedtime. Read a book or find something else to do. While you’re using screens, take a 20-second break every 20 minutes to look at something 20 feet away. If you get dry eyes when you look at screens for a long time, use artificial tears.