Short term memory was description by Atkinson & Shiffin in their modal model of memory in which they explained that information in STM lasts only for a very limited that is for about 15-30 seconds. In order to explain the methodology of STM, Brown/ Peterson & Peterson have conducted a study in which participants were asked to study 3 letters. Then they were asked to count backward by 3’s. eg: 100, 97, 94, 91, 88… for short period of time and later were asked to recall the letters they had originally seen. The result revealed for the 1st few trials show that people recalled most of the letters, however after several trials, the previous learnt letters produce interference and thus recall was poor. More ever after 5 seconds delay, people forgot approximately half of what they had seen.
Other techniques also have been used to examine short term memory. One among it is people were asked to study a long list of items such a many words as possible. The result reveled that there existed relationship between the position of the word presented and the probability of recalling the word which was termed as serial position curve/ effect.
Eg: recalling is accurate for the beginning & end words where as it was poor recall for the middle words some researches views that people were able to recall last words more accurately because the words were still in the STM at the time of recalling.
The size of STM
One way of measuring the size of STM is to count the no of word accurately recalled at eh end of the list typically the size of STM is estimated to be 2-7 items when the serial – position curve method is used.
STM size is measured in terms if memory span or the number if items in a row that can be correctly recalled. However, some researches view that pronunciation time is an important determination of STM. More over factors such as anxiety also influences the number of items that could be held in temporary storage.