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on January 4, 2007 at 2:26:14 pm

Human Memory: Short term and long term memory

Along with processes such as learning, perception and attention, memory is a crucial aspect of cognition. Indeed, when we ask precisely what ‘memory’ means it is impossible to define it independently from these other processes.

There is also a long history of scientific investigations into human memory, beginning with Ebbinghaus (1885), but the dominant view of memory has become the information processing approach. This suggests that memory can be best understood in terms of three essential stages of that involve the flow of information through memory: registration, storage and retrieval.


Different types of memory

Most psychologists make a distinction between different types of memory — particularly short-term and long-term memory. There is also a third type, the sensory register, which enables information to be stored very briefly so that feature and pattern recognition processes can operate.

Short-term memory and long-term memory are usually distinguished in terms of capacity, duration and coding (or encoding).


Capacity of STM

In a famous paper, George A Miller (1956) suggested that the capacity of STM was 7, plus or minus 2 items (7±2). This conclusion is typically supported by means of a digit-span experiment such as this Activity.


While investigations such as this support the idea that the capacity of STM is limited, determining exactly what the capacity of STM is has proved rather difficult. There are two basic reasons for this:

  • Different psychologists mean different things by the term capacity. For some it is how much the system can hold, storage capacity, while for others it is how much can be done on the information in storage, attentional capacity. If STM is seen as a kind of workbench then storage capacity refers to how many items can be placed on the workbench. Attentional capacity however is how many items can be worked on at any one time.
  • Determining what is meant by an item is difficult. Individual units can be grouped together to increase the capacity. For example, numbers can be grouped as dates, letters as words and so on. Each of these meaningful units is referred to as a ‘chunk’ and through chunking the capacity of STM can be increased significantly.


Coding in STM

The sensory register has no real organisation and so information is stored in more or less the same form as it arrived. However material in STM is highly transformed. Thus, no matter whether we read or hear a word, it will be stored in an acoustic form. Conrad (1964) demonstrated coding differences bewteen STM and LTM.

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