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[ 2009-01-14 11:18 ]

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.


Our 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 aren't always crystal-clear and are often limited to just the gist of what we saw or what happened.

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”记忆,它短暂地储存了我们正在想着的少数事情的信息;另一种长期的记忆,能够储存通过一生思考和经历得到的海量信息。在提供细节的水平上,这两种记忆也被认为是不同的。工作记忆给出的是有关我们当前正在思考的少数事情的清晰细节,而长期记忆给出的则是有关我们曾经见过或经历过的大量事情,其图像更加模糊。 这就是说,虽然我们在长期记忆中储存了很多东西,但其记忆细节并不总是清晰,而是经常只限于我们所见或已发生事情的要点梗概。

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 objects—including items such as backpacks, remote controls and toasters—that 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 it's 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 we've seen in a fairly detailed and precise form.


Of course, this finding raises the obvious question: if our memories aren't 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 can't always find that information when we want it. As this study reveals, if we're shown an object, we can often be very accurate and precise at being able to say whether we've seen it before. If we're 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 answer—without being prompted by a visual reminder. It seems that it is this voluntary searching mechanism that's prone to interference and forgetfulness. At least that's 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.



(来源:外文科普网站 实习生许雅宁 英语点津 Yvonne 编辑)


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