In English it's common to say, "I know this town like the back of my hand!" While we may know our towns really well, how well do we actually know our hands? Maybe not quite as well as we think, said a scientific study.
Matthew Longo and his team from University College London studied the left hands of 100 people. With their hands placed palms(手掌)down under a board, Longo's team gave the instruction to point to their knuckles(指关节) and fingertips with a marker. How did they do? Not that well.
"People think their hand is wider than it actually is," said Longo. He said they also seemed to think their fingers were shorter than their true lengths. People were most accurate when finding their thumbs, but became less accurate with each finger, up to their pinkies.
"It is connected to our sense of position," explained Longo. Humans know where different parts of our bodies are, even if we can't see them. "It tells us whether a joint(关节)is straight or not," said Longo. "We also need to know the distances between our joints," he went on. Our brains know the sizes and shapes of our bodies from the maps they make for themselves. "This experiment tried to find those maps," he said.
Maybe maps don't need to be perfect. But why aren't our brains more accurate? Longo said our brains "see" areas based on our sense of touch, with the stronger the sense of touch in a specific body part, the bigger that body part seems. An example is our lips. As they have more nerves than our noses, our brain's map shows our lips are bigger. The same thing can happen with body parts that have a lot of nerves. If you've ever had something stuck in your teeth, it probably felt huge! That's because our tongues also have lots of nerves.
If you want to have some fun, try this test with your classmates. Get some boards and some markers and have them mark the spots where they think their knuckles and fingertips are. Compare their hands to the marker spots and see how well they have performed.
