Memory: Encoding, Capacity and Duration
Features of each store – Encoding, duration and capacity
The way in which we remember information is shown by the Multi Story model. This suggests that there are 3 main areas in which information is stored. This involves the Sensory memory, Short term memory and Long term memory. These each have different ways of gaining information, how long it can hold that information, and how much it can actually hold.
Sensory Memory
The encoding of the sensory memory is simple. It takes information from one of the sensory organs, and hold it in the same form. For example, you are able to remember the sounds of waves crashing onto a beach from your memory (an example of Echoic memory).
The capacity of the Sensory memory was found by Sperling (1960). He carried out an experiment where he showed people a grid of letters for less than a second. He found that people, on average, recalled 4 letters. Using a different technique, he found that the iconic memory could hold up to 10 items. However, this information decays within 2 seconds or less.
Short Term Memory
The Short Term Memory encodes acoustically, meaning information is being learnt through sounds. This was found out by Conrad (1964), who presented a group of similar sounding letters to students and asked them to remember them. Then, he asked them to remember letters which were not acoustically the same. The students remembered more of the acoustically dissimilar letters than the rhyming letters (e.g B T D V). The information was encoded as a sound, even though it was presented visually.
The capacity of the STM was shown by Miller (1956), where he said that the STM can hold "The magic number seven, plus or minus two". Therefore the capacity of the STM on average is between 5 and 9 items. However...
Miller found out that by combining or organizing information into separate chunks, that the capacity of the STM could be a lot more. This is called Chunking, where the information is being made more meaningful with existing knowledge from your LTM.
The duration of the STM is very brief. There isn't really much research towards this, however some finding show that the STM only lasts for a few seconds before it decays, unless we rehearse the information. Peterson & Peterson (1959) carried out an experiment, where they got students to recall 3 letter combinations. The intervals between the groups of letters got longer as the experiment went on. During these intervals, the students were prevented from rehearsing by a counting task. This counting task could've been counting backwards in 3's from a set number. They found that after 3 seconds, 80% of students recalled correct information. However after 18 seconds only 10% of students recalled the correct trigram. This suggests that the STM fades within half a minute without rehearsal.
Long Term Memory
Baddeley (1966) showed people lists of 10 short words, one at a time. Some of these lists were semantically similar, and some were not. They were tested straight away, and then after a 20 minute delay. After 20 minutes, the people showed poor results on recalling the list of words that were semantically similar. This suggests that the LTM encodes semantically, or based around the meanings of words; we get similar meaning words confused.
The capacity of the LTM? Potentially unlimited. Things will decay with time. The duration is anything up to a lifetime. The duration is difficult to test, however Bahrick et al. (1975), tested graduates from the US. He showed them photos of their classmates years later. Bahrick et al found that there was a 90% accuracy on remembering names and faces 34 years after graduation. This however declined after 48 years, especially for faces.
