Many studies have been conducted to support the views that short and long term memory are different stores. In 1966 Baddeley carried out a study of encoding in short term memory and long term memory. Baddeley aimed to support earlier research that showed short term memory was largely based on acoustic code, and to find out whether either short term memory or long term memory was also acoustically coded. In addition, the study explored whether short term memory and long term memory was semantically coded. The participants were given sets of words to recall: acoustically similar, acoustically dissimilar, semantically similar or semantically dissimilar. The participants were then split in to 2 groups, one group was asked to recall the word immediately (STM), whereas the other group was asked to recall the words after an interval of 20 minutes (LTM)If the participants were asked to recall the word list immediately (STM) they did less well with acoustically similar words than with acoustically dissimilar words. When they recalled the words after an interval (LTM), they performed the same on the acoustic lists but there were differences on the semantic lists. The conclusions made supported the earlier research; this study suggested that short term memory is based largely on an acoustic code, whereas long term memory tends to be based on semantic codes.
Other studies into duration in short term memory and long term memory also support the views that short term memory and long term memory are separate stores.
In 1959 Peterson and Peterson studied duration in short term memory, they investigated how long information is retained in short term memory when verbal rehearsal is prevented. The participants in this study were given nonsense trigrams (e.g. CTG) and asked to recall them after 3,6,9,12,15 or 18 seconds. During the intervals the participants were given interference tasks (counting backward in trees from a tree-digit number) to prevent verbal rehearsal. Participants were able to recall 90% of the trigrams after 3 seconds but only 2% after 18 seconds. This shows the information held in short term memory has a very short duration before it disappears, if it is not rehearsed.
A similar study, this time into duration in long term memory was conducted in 1975 by Bahrick et al.,
The aim of this experiment was to study how long memories remain accessible in a natural context in which it is more likely that one can access very long term memory. The 400 participants involved were shown photographs of various people, including those from their high school year books, to test face recognition. They were asked to free recall names of those they attended high school with. The younger participants (who had left high school only 15 years before) were 90% accurate in face recall. This dropped to 70% when the participants who had left high school 48 years before. This study also supports the views that long term memory and short term memory are separate stores.
The studies above all support that the two memory stores are separate. If information is given to recall, without interference tasks this information is remembered. Studies show that if sufficient verbal rehearsal takes place then eventually the information will be transferred into the long term memory store.
