Short Term Memory

Short term memory

Short term memory, also referred to as STM is the memory of immediate events. Short term memories are measured in seconds and minutes because they have a short duration and they disappear unless they are rehearsed. Short term memory also has a very small capacity.

STM Capacity

Capacity is how much data or information can be held in a memory store at one given time.  STM has a very limited capacity.

Miller studied short term memory and found that 7+- 2 is the average number of items that can be held in the STM at one given moment. The items of information can be numbers, letters, words of even images. 

EVALUATION of STM capacity

Miller did not account for individual differences in people, other studies found that number recall increases with age. This may be caused by the increase in the brains capacity as we get older or as we age, we develop new strategies to improve digit span.   The capacity of STM may be even more limited, Cowan found that people recalled on average 4 chunks of information, this is also true for visual information. The size of the chuck also affects the capacity, smaller chunks had a longer memory span aka, more chunks were remembered.

Duration of STM

Duration is how long information is held in a memory before it is no longer available. STM has a short duration meaning the memory doesn't last very long.

Peterson and Peterson tested the duration of STM by giving participants a syllable and 3 digits to recall after different amounts of time, during which they had to count back in 3.'s. 3 sec= 90% correct  9 sec= 20% correct  18 sec = 2% correct This proves that STM has a short duration because after about 18 seconds the memory is no longer available.

Evaluation of STM duration

Testing the STM was artificial meaning it lack ecological validity. The task was to recall letters and numbers which is not an everyday task for the participants. But the study can be applied to real life in terms of memorising phone numbers and postcodes.   The results of the Peterson and Peterson study could have been caused by displacement. This is when the counting numbers overwrites the syllables that were to be remembered. This then shows that Peterson and Peterson weren't really studying duration but displacement.

Coding in STM

Coding is the way that information is processed in order to be stored in a memory.   The coding in STM is acoustic.

Baddeley investigated the short and long term memory to see how the memories where coded.  He found that STM was coded acoustically because participants found it more difficult to remember.

Evaluation of STM coding

STM may not be exclusively acoustic, some experiments have shown that visual coding also takes place in the short term memory store Participants were shown pictures and asked to say "la la la" in the retention interval to  prevent them from turning visual information into verbal codes. The participants where still able to recall the images.