There are two kinds of memory: short-term and long-term. Information in long-term memory can be recalled at a later time when it is needed. The information may be kept for days or weeks. Sometimes information in the long-term memory is hard to remember. Students taking exams often have this experience. In contrast, information in short-term memory is kept for only a few seconds, usually by repeating the information over and over. For example, you look up a number in the telephone book, and before you dial, you repeat the number over and over. If someone interrupts you, you will probably forget the number. In laboratory studies, subjects are unable to remember three letters after eighteen seconds if they are not allowed to repeat the letters to themselves.

Psychologists study memory and learning with both animal and human subjects. The two experiments here show how short-term memory has been studied.

Dr. Hunter studied short-term memory in rats. He used a special apparatus which had a cage for the rat and three doors. There was a light in each door. First the rat was placed in the closed cage. Next, one of the lights was turned on and then off. There was food for the rat only at this door. After the light was turned off, the rat had to wait a short time before it was released form its cage. Then, if it went to the correct door, it was rewarded with the food that was there. Hunter did this experiment many times. He always turned on the lights in a random order. The rat had to wait different intervals before it was released from the cage. Hunter found that if the rat had to wait more than ten seconds, it could not remember the correct door. Hunter's results show that rats have a short-term memory of about ten seconds.

Later, Dr. Henning studied how students who are learning English as a second language remember vocabulary. The subject in his experiment were 75 students at the University of California in Los Angeles. They represented all levels of ability in English: beginning, intermediate, advanced, and native-speaking students.

To begin, the subjects listened to a recording of a native speaker reading a paragraph in English. Following the recording, the subjects took a 15-question test to see which words they remembered. Each question has four choices. The subjects had to circle the word they had heard in the recording. Some of the questions had four choices that sound alike. For example, weather, whether, wither, and wetter are four words that sound alike. Some of the questions had four choices that have the same meaning. Method, way, manner, and system would be four words with the same meaning. Some of them had four unrelated choices. For instance, weather, method, love, and result could be used as four unrelated words. Finally the subjects took a language proficiency test.

Henning found that students with a lower proficiency in English made more of their mistakes on words that sound alike; students with a higher proficiency made more of their mistakes on words that have the same meaning. Henning's results suggest that beginning students hold the sound of words in their short-term memory, while advanced students hold the meaning of words in their short-term memory.

有两种记忆：短时记忆和长时记忆。处于长期记忆中的信息，在后来需要的时候能够回想起来。这一信息可以保持数天或数周。有时处于长时记忆中的信息很难记起。参加考试的学生经常会有这种经历。反之，短时记忆中的信息只能保持三两秒钟，通常还得再三复习这一信息。例如，你在一本电话号码簿中查到一个号码，在你还没拨号之前，你得再三复习这一号码。如果这时有人打扰了你，你也许会把这个电话号码忘了。通过实验研究表明，如果不准被测试的人复习，那么十八秒以后，被测试的人连三个字母都记不住。

心理学家们以动物和人这二者做测试对象分别研究了记忆和学习的情况。这里这两类试验都表明了研究短时记忆的情况。

亨特博士研究了大老鼠的短时记忆。他用了一种特殊装置，这种装置上有个鼠笼和三扇门。每扇门上都有一盏灯。首先，把大老鼠放到一个关着的鼠笼里。接着，把其中一盏灯打开然后再关上。只有在这扇门那里才有给老鼠听的东西。在把灯关掉以后，必须让这个老鼠等候一段短时期，这才把它从鼠笼中放出去。接下来，如果这个老鼠走对了门，那么，门那里摆着的食物就是对他的奖赏。亨特博士多次做过这种实验。他总是没有按固定顺序随便打开任何一盏灯。让老鼠等候的时间间隔也完全不同，然后才把大老鼠从鼠笼中放出去。亨特博士发现，如果老鼠必须等候10秒钟以上才放出，那它就记不住哪扇门是正确的。亨特博士实验的结果表明大老鼠能有大约10秒钟的短期记忆。

后来，享尼希博士研究了那些把英语作为第二种语言来学习的人，是怎样记生词的。他实验的对象是洛杉矶加州大学的75名学生。他们都是各种程度的英语学生中的代表人物：初级的、中级的、高级和以英语为母语的学生。

开头，先让受试者们听一段以英语为母语的人所朗读的一小段英文文章的录音。听了录音以后接着让受试者参加一次共15个问题的考试，看看他们都记住了哪些生词。每个问题有四个选择项。受试者必须圈出他们在录音中所听到的单词。每个问题有四个选择项听起来很像是一样的。例如：weather天气，whether是否，wither枯萎，wetter润湿剂。有些问题的选择项的意义像是一样的：method,way,manner和system.有些问题的四个选择项之间没有任何关连：weather,method,love和result.最后，受试者们都参加一次语言熟练程度的测试。

享尼希博士发现，凡是英语熟练程度低的学生多在声音相似的单词中会弄错；凡是英语熟练程度高的学生多在意义相似的词汇上会出错。享尼希的实验结果表明：初学者能把单词的声音保持短期记忆。享尼希的实验结果表明：初学者能把单词的声音保持短期记忆，而程度高的学生能把词汇的意义保持短期记忆。

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