Memory
Human short-term memory (STM) is very limited. Miller (1956) studied its capacity and found that no matter what type of item is stored, STM could only hold between five and nine items. This became known as the 'magic number, seven plus or minus two', although recent researchers have described its capacity as the number of items which can be pronounced in just under 30 seconds. The duration of STM is also limited to around 30 seconds unless information is rehearsed (Peterson and Peterson, 1959). STM uses information which are represented in STM as sounds.
Long-term memory (LTM) is the permanent memory store: information can be encoded to LTM straight away, and can last a lifetime. There is no limit to how much can be stored. Long-term memory tends to encode information based on the meaning of an item and this form of LTM is called semantic memory. There are two other LTM stores: episodic and procedural. Episodic memory is when you remember things that have happened to you and procedural memory is your memory for skills such as playing musical instruments or riding a bike.
In both STM and LTM, information goes through a three-stage process: it is encoded into a memory trace, stored, and then retrieved when needed.
Encoding involves taking information from the senses or from another memory store and placing it into a memory code. STM uses acoustic encoding and LTM uses semantic encoding. If items are encoded visual encoding.
Storage involves retaining information to be used at a later date. Memories must be consolidated on order to be retained, for example, when revising for exams. Walker et al. (2003) found that unbroken sleep is vital to the brain processes involved in procedural memories being consolidated. The aim of the experiment was to study role of waking hours prior to sleep in learning/interference of procedural memories.
"Although it was clear that 4-12 hours of waking did not enhance behavioural performance, we did not know whether this waking period could stabilise the motor memory".
There were 100 right-handed subjects, aged 18-27 and without psychiatric or sleep disorder histories. Subjects performed a sequential finger tapping motor skill task.
Retrieval is where information is brought back from the memory store when needed. Sometimes retrieval is difficult: things may be on the tip of your tongue. There are two types of retrieval: free recall and recognition. A cue is a hint or trigger which helps retrieval, such as the letter a word starts with.
