In addition, information selected for further processing passes from the sensory memory store into the short-term memory, it is thought that the short-term memory holds information in the form of images, sounds or meanings, information in the short-term memory is kept alive by continual rehearsal of it, an example study for the life-span of the short-term memory was conducted by Peterson and Peterson (1959) in which they gave participants a constant trigram to remember and then a large number. To prevent rehearsal, they counted backwards in threes from the number and then recalled the trigram. Participants were unable to recall the trigram at all after 18-30 seconds indicating that this is was the life span of items in the short-term memory.
Long term memory is thought to have an unlimited capacity to retain information, it can hold material for long periods of time, coding of information is mainly semantic within the long term store. As the material passes through the stores, it becomes more sunk in and compressed. The duration of long term memory is anything up to a lifetime. Long term memory is very difficult to test for exact duration, but bahrick (1975) tested a selected group of us graduates.
This testing involved several stages;
1. A name and photo matching test.
2. A name recognition test.
3. A photo recognition test where they were asked to identify former classmates in a set of fifty photo, only some of which were their classmates.
4. Free recall of the names of as many former classmates as possible.
. Bahrick and colleagues used high-school yearbooks to test long-term memory for names and faces, many years after the memories had been encoded. Using 400 participants in their study, they found 90% accuracy in identifying names and faces among those tested within 15 years of leaving school. Even for the participants who had left school nearly 50 years before the experiment, identification of names and faces stood at 70-80%. Considering the duration as well as the fact that the latter group were on average much older, this is a small difference.
We have evidence to support the model. For example brain scanning (MRI) has been carried and the scans show that separate parts of the brain are being used as different tasks are carried out. This evidence backs up the model using separate stores for different memory.
Several cases of patients who have suffered brain damage to their hippocampus & have memory deficits to there H.M, Clive wearing and K.F. There memory less tends to be selective supporting the idea of separate stores for different types of memory.