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 from its cage)h . 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 then 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 subjects in bhis 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 )Each question had 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 .       He was rewarded with 5000 yuan for his bravery.   I hate the eight-year old boy, for he is too naughty.