试试这个有趣的实验。这一心理现象被称为两点辨别觉，可以用于检测神经损伤。



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选材／校对／翻译：hqj5715
Here's a fun experiment that tells you something about your nervous system. You can do it on yourself, but it works best if you do it on someone else, and vice versa. All you need is two pointed objects, such as pencils. Have your friend close her eyes, and tell her you're going to touch the inside of her forearm with the two pencil points simultaneously about eight inches apart. Then you're going to lift the points and bring them down again and again, each time moving the points closer together. She's to tell you when you're touching her with only one pencil. It's surprising that when she thinks she's being touched by only one point both are still touching her arm, and they are one to two inches apart! Now do the same thing on the pad at the end of her index finger, but start with the points about an inch apart. This time when she thinks she feels only one point the two will be about 1/8 inch apart. Why does she feel only one point when she's being touched by two? And why on the forearm are the points as much as two inches apart when one point is felt, but only 1/8 inch apart on the fingertip? It's because some areas of the body, such as the fingertips have more nerves going to them. And, the areas of the brain which receive information from these sensitive areas of the body have a greater density of nerves. So, since more nerves are present to detect sensations these areas are more discriminating.
这是一个可以告诉你一些关于你神经系统信息的有趣实验。你可以自己独自做这个实验，但是如果在别人身上做效果会更好，相反也是如此。你所需要的只是两个尖尖的物体，比如铅笔。 让你的朋友闭上眼睛，告诉她你准备用两支铅笔同时触碰其前臂的内侧，两支铅笔相距约8英寸。然后你会抬起铅笔并一次一次的刺下，每一次刺下的时候使两个铅笔的距离拉近。当你只用一个铅笔刺其前臂的时候她会告诉你。 奇怪的是当她认为只有一个铅笔刺其前臂的时候，两支铅笔仍在同时刺向她，而且两支铅笔相距有1到2英寸。 现在我们在她食指的肉趾上做相同的事情，但是开始时两支铅笔的距离改为约1英寸。当她感觉只有一点时两个铅笔相距约1/8英寸。 为什么用两个铅笔刺她是她只能感觉到一个？为什么当感觉只有一点时在前臂的距离约为2英寸，而在手指上却只有1/8英寸。 这是因为身体的某些部位，例如手指具有较多的神经分布。而且，接收来自身体这些敏感部位信息的大脑区域神经密度较高。因此，既然有较多的神经用于感知感觉，那么这些区域就有较强的区别能力。