[00:00.00] How Your Memory Works

[00:04.49]In all human communication,

[00:09.04]information is sent from one person's memory to another.

[00:15.70]No matte how the message is sent,

[00:20.24]it must arrive in a form that can be understood,

[00:25.81]retained,and later recalled by the brain.

[00:31.35]How do these memory processes function?

[00:37.72]Before answering this question,

[00:42.27]we need to consider the fact that there are two kinds of memory:

[00:48.72]short-term and long-term memory.

[00:53.37]Psychologists know a great deal about the former kind of memory,

[01:00.53]but they know very little about the latter kind.

[01:06.17]Your short-term memory

[01:10.14]can hold only five to seven"bits"or items of information.

[01:17.87]However,unless your repeat that information

[01:23.30]to yourself over and over again,you will forget it in less than a minute.

[01:30.85]This temporary memory is used when you try to remember a name

[01:37.99]or telephone number that someone told you a moment ago.

[01:43.84]Short-term memory

[01:47.70]plays an important to test in thinking and understanding.

[01:54.16]Many psychologists perform a classical experiment

[02:00.11]to test the capacity of short-term memory.

[02:05.96]Subjects sit in small booths,wear headphones,

[02:11.92]and look at a small TV screen lighted in front of them.

[02:18.16]A series fo numbers is flashed on the screen,

[02:23.83]and the subjects and asked to identify a specific number

[02:30.47]to the right of another number in the scries.

[02:35.92]The psychologists discover that when the questions are asked

[02:41.99]immediately after the number series is flashed off the screen,

[02:48.54]the subjects can answer quite well;

[02:53.40]the series is easily remembered as a "memory photograph."

[03:00.24]If the questions are delayed even one half second,however,

[03:07.40]memory photographs fade away and accuracy is lowered greatly.

[03:14.95]The subjects also forget the series quickly

[03:20.70]when any sort of interruption occurs

[03:25.66]that blocks their search for a particular number.

[03:31.20]In another interesting experiment to test short-term memory,

[03:38.54]psychologists asked volunteers

[03:44.00]to memorize a short list of numbers such as 2.4.7.8.

[03:52.05]Subjects were then asked to decide quickly

[03:57.69]whether a particular number-for example,7-was in the list.

[04:04.53]The scientists discovered

[04:08.27]that the subjects were able to search 25 to 30 memorized numbers per second,

[04:16.50]and the tests also showed that

[04:20.83]when the people mentally searched their memorized lists,

[04:26.29]they would not stop as soon as they recogized a matching number such as 7,

[04:33.14]but continued through the entire set.

[04:38.10]Surprisingly,people need to mentally recite the entire memorized list;

[04:46.46]it is a difficult to understand why people must continue searching

[04:53.20]after they have discovered a matching number.

[04:58.34]"A possible answer",the scientists explained,

[05:03.67]"is that searcing through the whole list may actually go faster

[05:09.92]than a search that stops part way through it."

[05:15.17]In fact,when the psychologists used a different task

[05:21.02]that required the subjects to stop searching

[05:25.98]when they found the test number,their search became much slower.

[05:32.51]Scientists are interested in finding out

[05:37.76]how short-term memory becomes long-term memory.

[05:44.71]They know that the process is influenced by age,

[05:50.46]genetics,hormones and the environment.

[05:55.71]Also,they know that the brain stores information

[06:01.67]in various ways at different times.

[06:06.92]The same event is organized and stored quite differently,

[06:13.08]depending on whether a person is calm,

[06:17.84]in panic,or somewhere in between.

[06:22.98]Depressed persons can recall unpleasant memories quickly

[06:29.64]because these memories are more meaningful to them;

[06:35.18]that is,the memories are more directly associated

[06:41.53]with people's unpleasant experiences.

[06:47.17]The process of how memory photographs are stored

[06:52.92]and later recalled still remains an unanswered question.