Pupils (瞳孔) respond to more than just light. They can indicate one’s interest or mental exhaustion. Pupil dilation (扩大) is even used by the police to detect lies. Now work conducted in our laboratory suggests that the pupil size is closely related to individual differences in intelligence. The larger the pupils are, the higher the intelligence is, as measured by the tests of reasoning, attention and memory.

We first uncovered this surprising relationship while studying differences in the amount of mental effort people used to complete memory tasks. We used pupil dilation as an indicator of effort, a technique psychologist Dani Kahneman popularized in the 1960s and 1970s. When we discovered a relationship between the pupil size and intelligence, we weren’t sure if it was real or what it meant.

Curiously, we conducted several large-scale studies in which we recruited more than 500 people aged 18 to 55 from the Atlanta community. We measured the participants’ pupils at rest while they stared at a blank computer screen for up to four minutes with an eye tracker. All the while, the eye tracker was recording. Using the tracker, we then calculated each participant’s pupil size.

To be clear, the pupil size refers to the diameter (直径) of the black circular aperture in the center of the eye. The pupil is surrounded by the colorful area known as the iris (虹膜), which is responsible for controlling the size of the pupil. Pupils become tighter and smaller in response to bright light, so we kept the laboratory dim (昏暗的) for all participants.

In the next part of the experiment, the participants completed a series of tests designed to measure “fluid intelligence”, the capacity to reason through new problems, “working memory capacity”, the ability to remember information over a period of time, and “attention control”, the ability to focus attention amid distractions and interference.

We found that a larger pupil size was correlated with greater fluid intelligence, attention control and, to a lesser degree, working memory capacity—indicating a fascinating relationship between the brain and the eyes. Interestingly, the pupil size was negatively correlated with age: older participants tended to have smaller pupils. Once standardized for age, however, the relationship between the pupil size and intelligence remained.

The ocean is a huge body of saltwater that covers about 71 percent of Earth’s surface. An estimated 97 percent of the world’s water is found in the ocean. Because of this, the ocean has a very important impact on weather, temperature, and the food supply of humans and other organisms. However, it remains unknown. More than 80 percent of the ocean has never been mapped, explored, or even seen by humans, while a far greater percentage of the surfaces of Moon and the planet Mars has been mapped and studied.

Although there is much more to learn, ocean researchers have already made some amazing discoveries. For example, we know that the ocean contains big mountain ranges and deep canyons (峡谷), just like those on land. The height of the word’s tallest mountain Mount Everest in the Himalayas, measuring 8.84 kilometers (5.49mies) high-would not even break the surface of the water if it were placed in the Pacific Ocean’s Mariana Trench or Philippine Trench, two of the deepest parts of the ocean. The average depth of the entire ocean is 3,720 meters

It is unknown how many different species call the ocean their home. With many ocean ecosystems suffering from rising sea temperatures, pollution and other problems, some ocean researchers believe the number of species is dropping. Still, there may be many positive surprises awaiting them in the years ahead. It could be that more than 90 percent of the ocean’s species are still undiscovered, with some scientists estimating that there are anywhere between a few hundred thousand and a few million more to be discovered. Currently, scientists know of around 226.000 ocean species. Since the ocean is so vast, there is plenty for future ocean researchers from all corners of the globe to explore and discover.