我们为什么总是健忘？我们为什么总是健忘？The brain can store a vast number of memories, so why cant we find these memories when we need to? A new study provides insights into this question.By Edward K. Vogel and Trafton DrewOur brains are crammed with a massive amount of memories that we have formed over a lifetime of experiences. These memories range from the profound (who am I and how did I get here?) to the most trivial (the license plate of the car at a stoplight). Furthermore, our memories also vary considerably in their precision. Parents, for instance, often know the perils of a fuzzy memory when shopping for a birthday gift for their child: remembering that their son wanted the G.I. Joe with Kung Fu Grip rather than the regular G.I. Joe could make an enormous difference in how well the gift is received. Thus, the “fuzziness” of our memory can often be just as important in our daily lives as being able to remember lots and lots of information in the first place.Different Levels of Detail for Different Types of Memory?In the past several decades, cognitive psychologists have determined that there are two primary memory systems in the human mind: a short-term, or “working,” memory that temporarily holds information about just a few things that we are currently thinking about; and a long-lasting memory that can hold massive amounts of information gained through a lifetime of thoughts and experiences. These two memory systems are also thought to differ in the level of detail they provide: working memory provides sharp detail about the few things we are presently thinking about, whereas long-term memory provides a much fuzzier picture about lots of different things we have seen or experienced. That is, although we can hold lots of things in long-term memory, the details of the memory arent always crystal-clear and are often limited to just the gist of what we saw or what happened.A recently published study by Timothy F. Brady, a cognitive neuroscientist at the Massachusetts Institute of Technology, and colleagues suggests that these long-term memories may not be nearly as fuzzy as once thought, however. In their work, the researchers asked subjects to try to remember 3,000 pictures of common objectsincluding items such as backpacks, remote controls and toastersthat were presented one at a time for just a few seconds each. At the end of this viewing phase, the researchers tested subjects memory for each object by showing them two objects and asking which one they had seen before. Not surprisingly, subjects were exceptionally good (more than 90 percent correct) even though there were thousands of objects to remember. This high success rate attests to the massive storage ability of long-term memory. What was most surprising, however, was the amazing level of detail that the subjects had for all of these memories. The subjects were just as good at telling the difference between two pictures of the same object even when the objects differed in an extremely subtle manner, such as a pair of toasters with slightly different slices of bread.If Its Not Fuzzy, Why Do We Still Forget Things?This new work provides compelling evidence that the enormous amount of information we hold in long-term memory is not so uncertain after all. It seems that we actually hold representations of things weve seen in a fairly detailed and precise form.Of course, this finding raises the obvious question: if our memories arent all that fuzzy, then why do we often forget the details of things we want to remember? One explanation is that, although the brain contains detailed representations of lots of different events and objects, we cant always find that information when we want it. As this study reveals, if were shown an object, we can often be very accurate and precise at being able to say whether weve seen it before. If were in a toy store and trying to remember what it was that our son wanted for his birthday, however, we need to be able to voluntarily search our memory for the right answerwithout being prompted by a visual reminder. It seems that it is this voluntary searching mechanism thats prone to interference and forgetfulness. At least thats our story when we come home without the Kung Fu Grip G.I. Joe.Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters editor Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust Was a Neuroscientist.大脑能够储存巨大数量的记忆，那么为什么在需要的时候我们会回忆不起来呢？ 一项新的 研究为这一问题提供了见解。作者 Edward K. Vogel and Trafton Drew我们的大脑里填满了在我们整个人生经历中形成的大量记忆。 这些记忆可以很深奥（我是 谁还有我怎么来到这的？）也可以是最琐碎的（红灯停车时看到的某辆车的牌照） 。 此外， 我们记忆的准确度在相当程度上也存在着分别。 打个比方，父母们大多都明白在给他们的 孩子买一份生日礼物时，如果记忆不清楚会有什么不良后果。 记得他们的孩子更想要的是 耍功夫把式的 G.I. Joe（眼镜蛇部队） ，而非普通的 G.I. Joe，会显著影响孩子接受礼物的乐 意程度。 因此，在日常生活的大多数情况下，我们记忆的“模糊性”与一开始就能够记住很 多很多信息是同等重要的。不同类型的记忆有不同的细节水平？过去的几十年中，认知心理学家们已经确定，在人类大脑中主要存在着两种记忆系统。 一 种短期的，或者“工作”的记忆短暂地储存了我们正在想着的少数事情的信息；另